Synthesis and biological evaluation of novel demethylzeylasteral derivatives as potential anticancer agents.

Demethylzeylasteral (DEM), a class of terpenoids isolated from natural plants, frequently exhibits moderate or limited inhibitory effect on tumor growth across multiple cancer types. Thus, here we attempted to elevate the anti-tumor efficacy of DEM by altering active groups in its chemical structure. Initially, we synthesized a series of novel DEM derivatives 1-21 through performing a series of modifications of its phenolic hydroxyl groups at C-2/3, C-4 and C-29 positions. The anti-proliferative activities of these new compounds were subsequently assessed using three human cancer cell line models (A549, HCT116 and HeLa) and CCK-8 assay. Our data showed that compared to original DEM compound, derivative 7 exhibited remarkable inhibition effect on A549 (16.73 ± 1.07 µM), HCT116 (16.26 ± 1.94 µM) and HeLa (17.07 ± 1.09 µM), almost reaching to the same level of DOX. Moreover, the structure-activity relationships (SARs) of the synthesized DEM derivatives were discussed in detail. We found that treatment with derivative 7 only led to moderate cell cycle arrest at S-phase in a concentration-dependent manner. Meanwhile, derivative 7 treatment markedly induced apoptosis in tumor cells. Consistent with this observation, our subsequent docking analysis showed that derivative 7 is capable of activating caspase-3 through interaction with the His 121 and Gly 122 residues of the enzyme. Overall, we have developed a new series of DEM derivatives with elevated anti-tumor efficacy relative to its parent form. The results suggested that derivative 7 has great potential to be employed as an anticancer agent candidate for natural product-based cancer chemotherapy.

Targeting receptor tyrosine kinases in ovarian cancer: Genomic dysregulation, clinical evaluation of inhibitors, and potential for combinatorial therapies.

Epithelial ovarian cancer (EOC) remains one of the leading causes of cancer-related deaths among women worldwide. Receptor tyrosine kinases (RTKs) have long been sought as therapeutic targets for EOC, as they are frequently hyperactivated in primary tumors and drive disease relapse, progression, and metastasis. More recently, these oncogenic drivers have been implicated in EOC response to poly(ADP-ribose) polymerase (PARP) inhibitors and epigenome-interfering agents. This evidence revives RTKs as promising targets for therapeutic intervention of EOC. This review summarizes recent studies on the role of RTKs in EOC malignancy and the use of their inhibitors for clinical treatment. Our focus is on the ERBB family, c-Met, and VEGFR, as they are linked to drug resistance and targetable using commercially available drugs. The importance of these RTKs and their inhibitors is highlighted by their impact on signal transduction and intratumoral heterogeneity in EOC and successful use as maintenance therapy in the clinic through suppression of the VEGF/VEGFR axis. Finally, the therapeutic potential of RTK inhibitors is discussed in the context of combinatorial targeting via co-inhibiting proliferative and anti-apoptotic pathways, epigenomic/transcriptional programs, and harnessing the efficacy of PARP inhibitors and programmed cell death 1/ligand 1 immune checkpoint therapies.

CD151 drives cancer progression depending on integrin α3ß1 through EGFR signaling in non-small cell lung cancer.

BACKGROUND: Tetraspanins CD151, a transmembrane 4 superfamily protein, has been identified participating in the initiation of a variety of cancers. However, the precise function of CD151 in non-small cell lung cancer (NSCLC) remains unclear. Here, we addressed the pro-tumoral role of CD151 in NSCLC by targeting EGFR/ErbB2 which favors tumor proliferation, migration and invasion. METHODS: First, the mRNA expression levels of CD151 in NSCLC tissues and cell lines were measured by RT-PCR. Meanwhile, CD151 and its associated proteins were analyzed by western blotting. The expression levels of CD151 in NSCLC samples and its paired adjacent lung tissues were then verified by Immunohistochemistry. The protein interactions are evaluated by co-immunoprecipitation. Flow cytometry was applied to cell cycle analysis. CCK-8, EdU Incorporation, and clonogenic assays were used to analyze cell viability. Wound healing, transwell migration, and matrigel invasion assays were utilized to assess the motility of tumor cells. To investigate the role of CD151 in vivo, lung carcinoma xenograft mouse model was applied. RESULTS: High CD151 expression was identified in NSCLC tissues and cell lines, and its high expression was significantly associated with poor prognosis of NSCLC patients. Further, knockdown of CD151 in vitro inhibited tumor proliferation, migration, and invasion. Besides, inoculation of nude mice with CD151-overexpressing tumor cells exhibited substantial tumor proliferation compared to that in control mice which inoculated with vector-transfected tumor cells. Noteworthy, we found that overexpression of CD151 conferred cell migration and invasion by interacting with integrins. We next sought to demonstrate that CD151 regulated downstream signaling pathways via activation of EGFR/ErbB2 in NSCLC cells. Therefore, we infer that CD151 probably affects the sensitivity of NSCLC in response to anti-cancer drugs. CONCLUSIONS: Based on these results, we demonstrated a new mechanism of CD151-mediated tumor progression by targeting EGFR/ErbB2 signaling pathway, by which CD151 promotes NSCLC proliferation, migration, and invasion, which may considered as a potential target of NSCLC treatment.

The Context-Dependent Impact of Integrin-Associated CD151 and Other Tetraspanins on Cancer Development and Progression: A Class of Versatile Mediators of Cellular Function and Signaling, Tumorigenesis and Metastasis.

As a family of integral membrane proteins, tetraspanins have been functionally linked to a wide spectrum of human cancers, ranging from breast, colon, lung, ovarian, prostate, and skin carcinomas to glioblastoma. CD151 is one such prominent member of the tetraspanin family recently suggested to mediate tumor development, growth, and progression in oncogenic context- and cell lineage-dependent manners. In the current review, we summarize recent advances in mechanistic understanding of the function and signaling of integrin-associated CD151 and other tetraspanins in multiple cancer types. We also highlight emerging genetic and epigenetic evidence on the intrinsic links between tetraspanins, the epithelial-mesenchymal transition (EMT), cancer stem cells (CSCs), and the Wnt/ß-catenin pathway, as well as the dynamics of exosome and cellular metabolism. Finally, we discuss the implications of the highly plastic nature and epigenetic susceptibility of CD151 expression, function, and signaling for clinical diagnosis and therapeutic intervention for human cancer.

BRD4 modulates vulnerability of triple-negative breast cancer to targeting of integrin-dependent signaling pathways.

PURPOSE: Stemming from a myriad of genetic and epigenetic alterations, triple-negative breast cancer (TNBC) is tied to poor clinical outcomes and aspires for individualized therapies. Here we investigated the therapeutic potential of co-inhibiting integrin-dependent signaling pathway and BRD4, a transcriptional and epigenetic mediator, for TNBC. METHODS: Two independent patient cohorts were subjected to bioinformatic and IHC examination for clinical association of candidate cancer drivers. The efficacy and biological bases for co-targeting these drivers were interrogated using cancer cell lines, a protein kinase array, chemical inhibitors, RNAi/CRISPR/Cas9 approaches, and a 4 T1-Balb/c xenograft model. RESULTS: We found that amplification of the chromosome 8q24 region occurred in nearly 20% of TNBC tumors, and that it coincided with co-upregulation or amplification of c-Myc and FAK, a key effector of integrin-dependent signaling. This co-upregulation at the mRNA or protein level correlated with a poor patient survival (p < 0.0109 or p < 0.0402, respectively). Furthermore, we found that 14 TNBC cell lines exhibited high vulnerabilities to the combination of JQ1 and VS-6063, potent pharmacological antagonists of the BRD4/c-Myc and integrin/FAK-dependent pathways, respectively. We also observed a cooperative inhibitory effect of JQ1 and VS-6063 on tumor growth and infiltration of Ly6G+ myeloid-derived suppressor cells in vivo. Finally, we found that JQ1 and VS-6063 cooperatively induced apoptotic cell death by altering XIAP, Bcl2/Bcl-xl and Bim levels, impairing c-Src/p130Cas-, PI3K/Akt- and RelA-associated signaling, and were linked to EMT-inducing transcription factor Snail- and Slug-dependent regulation. CONCLUSION: Based on our results, we conclude that the BRD4/c-Myc- and integrin/FAK-dependent pathways act in concert to promote breast cancer cell survival and poor clinical outcomes. As such, they represent promising targets for a synthetic lethal-type of therapy against TNBC.

Epigenetic Input Dictates the Threshold of Targeting of the Integrin-Dependent Pathway in Non-small Cell Lung Cancer.

We investigated the therapeutic potential of targeting integrin/FAK-dependent signaling, an adhesion receptor-mediated pathway that has been increasingly linked to non-small cell lung cancer (NSCLC) malignancy. Our analysis of the TCGA cohort showed that a subset of pro-tumorigenic integrins, including α1ß1, α2ß1, α3ß1, α5ß1, and α6ß4, were frequently amplified or upregulated at the genomic or mRNA level in KRAS or EGFR mutation/overexpression-enriched adenocarcinomas. These alterations appeared complementary, correlated with poor patient survival (p < 0.0072), and were collaborative with KRAS mutation-coupled αv integrins (p < 0.00159). Since integrin/FAK-dependent signaling is tightly coupled with normal human physiology, we sought to use a synthetic lethal-type targeting comprising of VS-6063, a chemical inhibitor of integrin-mediated FAK activity, and A549 cells, which carry a KRAS mutation and EGFR overexpression. Our screening analysis revealed that JQ1 and IBET-762, inhibitors of epigenetic reader BRD4, and LBH589, a pan inhibitor of histone deacetylases (HDACs), exhibited synergy with VS-6063 in mitigating tumor cell viability. This epigenetic link was corroborated by strong effects of additional inhibitors and RNAi-mediated knockdown of FAK and BRD4 or its downstream effector, c-Myc. Low doses of JQ1 (≤0.5 µM) markedly escalated efficacy of VS-6063 across a panel of 10 NSCLC cell lines. This catalyst-like effect is in line with the oncogenic landscape in the TCGA cohort since c-Myc falls downstream of the KRAS and EGFR oncogenes. Mechanistically, co-inhibiting the integrin-FAK and BRD4/c-Myc axes synergistically induced apoptotic cell death and DNA damage response, and impaired stemness-associated tumorsphere formation. These effects were accompanied by a marked inhibition of Akt- and p130Cas/Src-dependent signaling, but not Erk1/2 activity. Meanwhile, JQ1 alone or in combination with VS-6063 attenuated cell-cell adhesion and extracellular matrix (ECM)-dependent cell spreading, which is reminiscent of phenotype induced by malfunctional E-cadherin or integrins. Paradoxically, this phenotypic impact coincided with downregulation of epithelial-mesenchymal transition (EMT)-inducting transcription factor ZEB1 or Snail. Finally, we showed that the effect of the VS-6063/JQ1 combination was nearly equivalent to that of VS-6063 plus Carboplatin or Osimertinib. Overall, our study indicates that the integrin/FAK and BRD4/c-Myc axes cooperatively drive NSCLC virulence, and a co-targeting may provide a line of therapy capable of overcoming EGFR/KRAS-driven malignancy.

Integrin-associated CD151 is a suppressor of prostate cancer progression.

Owing to the complexity of interacting molecular networks on the cell surface, integrin-associated tetraspanin CD151 remains controversial regarding its clinical importance and functional impact in prostate cancer. The current study evaluated dynamics and clinical importance of CD151 expression and its function in prostate cancer by IHC analysis of two independent patient cohorts (n=80, 181), bioinformatic interrogation of the TCGA database, and evaluation of gene knockdown effect at the cellular level. Our data showed that aside from high mRNA expression, CD151 was primarily localized to intercellular junctions at the plasma membrane in normal prostate glands or benign tissues, regardless of nature of antibodies used. By contrast, in primary tumors from patients with metastatic disease, CD151 was largely localized in the cytosol. Furthermore, the level of the cell-cell junction-linked CD151 was inversely associated with Gleason grade and tumor stage (P<0.001 for both). The portion of primary tumors expressing junctional CD151 was also three-fold less in the metastatic patient population than its counterpart (P<0.001). In line with these observations, CD151 and its associated α3ß1 or α6ß4 integrin inversely correlated with androgen receptor (AR) at the mRNA level (Spearman coefficient: -0.44, -0.48 and -0.42) in the TCGA cohort. Expression of these adhesion molecules also correlated with DNA methylation in their promoters (Spearman coefficient: -0.37, -0.71 and -0.82). Combined, these data suggest that CD151 and associated integrins are linked to tumor metastasis through AR and the epigenetic program. Meanwhile, CD151 knockdown in E-cadherin-positive tumor cells led to increased cell proliferation and induction of the epithelial-mesenchymal transition (EMT)-like phenotype. Given the strong RGD-binding integrin dependence of EMT-featured tumor cells, we examined focal adhesion kinase (FAK), their key signaling effector, in the above patient cohorts. In contrast to CD151, FAK exhibited positive correlation with tumor grade and stage as well as AR and p53 inactivation at either mRNA, protein or genomic level. Taken together, our results suggest that CD151 represses prostate cancer by antagonizing cell proliferation, EMT and the signaling of RGD-binding integrins. Since this anti-tumorigenic role is prone to the AR-mediated transcriptional and epigenetic regulation, CD151 and possibly α3ß1 and α6ß4 integrins are of potential biomarkers for metastatic prostate cancer.

Deletion of tetraspanin CD151 alters the Wnt oncogene-induced mammary tumorigenesis: A cell type-linked function and signaling.

Tetraspanin CD151 is increasingly implicated as a multifaceted mediator of cancer development and progression. Here we investigated the role of CD151 in breast cancer in the context of the Wnt oncogenic activation. Our data showed that removal of one or both of CD151 alleles in the MMTV-Wnt1 model significantly decreased the tumor-free survival of mice from 34 weeks on average to 22 weeks and 18 weeks, respectively. This effect coincided with an accelerated tumor growth and an increased number of Ki-67+ proliferative cells. Mechanistically, the CD151-deficient tumors were largely ER+, and exhibited hyperactivation of the Wnt pathway as reflected by a marked upregulation in ß-catenin and Cyclin D1, and their target genes. In addition, E-cadherin displayed a cytosolic distribution and transcription factor Snail was markedly upregulated. Collectively, this data implies that CD151 suppresses the Wnt1-driven tumorigenesis, at least in part, via counteracting the epithelial-mesenchymal transition (EMT)-like program in luminal epithelial cells. Meanwhile, the proportion of tumor cells expressing CK5 or p63, the biomarkers of myoepithelial/basal cells, markedly decreased in the absence of CD151. This change was accompanied by a decreased invasiveness of tumors and their incompetence to form a long-term cell culture. Consistent with this basal cell-linked role, the CD151 downregulation impairs mammosphere formation in MCF-10A cells and the defect was rescued by re-expression of intact CD151 ORF, but not its integrin binding-defective mutant. Overall, our study suggests that CD151 is a key player in the Wnt oncogene-driven tumorigenesis and impacts breast cancer malignancy in a cell type-dependent manner.

The metastasis suppressor NME1 inhibits melanoma cell motility via direct transcriptional induction of the integrin beta-3 gene.

Expression of the metastasis suppressor NME1 in melanoma is associated with reduced cellular motility, invasion, and metastasis, but mechanisms underlying these activities are not completely understood. Herein we report a novel mechanism through which NME1 drives formation of large, stable focal adhesions (FAs) in melanoma cells via induction of integrin ß3 (ITGß3), and in one cell line, concomitant suppression of integrin ß1 (ITGß1) transcripts. Forced expression of NME1 resulted in a strong activation of the promoter region (-301 to +13) of the ITGB3 gene. Chromatin immunoprecipitation (ChIP) analysis revealed the transcriptional induction was associated with direct recruitment of NME1 and an increase in the epigenetic activation mark, acetylation of histone 3 on lysine 27 (H3K27Ac) to a 1 kb stretch of 5'-flanking sequence of the ITGB3 gene. Unexpectedly, NME1 did not affect the amount either ITGß1 or ITGß3 proteins were internalized and recycled, processes commonly associated with regulating expression of integrins at the cell surface. The ability of NME1 to suppress motile and invasive phenotypes of melanoma cells was dependent on its induction of ITGß3. Expression of ITGß3 mRNA was associated with increased disease-free survival time in melanoma patients of the TCGA collection, consistent with its potential role as an effector of the metastasis suppressor function of NME1. Together, these data indicate metastasis suppressor activity of NME1 in melanoma is mediated by induction of ITGB3 gene transcription, with NME1-driven enrichment of ITGß3 protein at the cell membrane resulting in attenuated cell motility through the stabilization of large focal adhesions.

Chronic ethanol exposure enhances the aggressiveness of breast cancer: the role of p38γ.

Both epidemiological and experimental studies suggest that ethanol may enhance aggressiveness of breast cancer. We have previously demonstrated that short term exposure to ethanol (12-48 hours) increased migration/invasion in breast cancer cells overexpressing ErbB2, but not in breast cancer cells with low expression of ErbB2, such as MCF7, BT20 and T47D breast cancer cells. In this study, we showed that chronic ethanol exposure transformed breast cancer cells that were not responsive to short term ethanol treatment to a more aggressive phenotype. Chronic ethanol exposure (10 days - 2 months) at 100 (22 mM) or 200 mg/dl (44 mM) caused the scattering of MCF7, BT20 and T47D cell colonies in a 3-dimension culture system. Chronic ethanol exposure also increased colony formation in an anchorage-independent condition and stimulated cell invasion/migration. Chronic ethanol exposure increased cancer stem-like cell (CSC) population by more than 20 folds. Breast cancer cells exposed to ethanol in vitro displayed a much higher growth rate and metastasis in mice. Ethanol selectively activated p38γ MAPK and RhoC but not p38α/ß in a concentration-dependent manner. SP-MCF7 cells, a derivative of MCF7 cells which compose mainly CSC expressed high levels of phosphorylated p38γ MAPK. Knocking-down p38γ MAPK blocked ethanol-induced RhoC activation, cell scattering, invasion/migration and ethanol-increased CSC population. Furthermore, knocking-down p38γ MAPK mitigated ethanol-induced tumor growth and metastasis in mice. These results suggest that chronic ethanol exposure can enhance the aggressiveness of breast cancer by activating p38γ MAPK/RhoC pathway.

Role of MCP-1 in alcohol-induced aggressiveness of colorectal cancer cells.

Epidemiological studies demonstrate that alcohol consumption is associated with an increased risk of colorectal cancer (CRC). In addition to promoting carcinogenesis, alcohol may also accelerate the progression of existing CRC. We hypothesized that alcohol may enhance the aggressiveness of CRC. In this study, we investigated the effect of alcohol on the migration/invasion and metastasis of CRC. Alcohol increased the migration/invasion of colorectal cancer cells (DLD1, HCT116, HT29, and SW480) in a concentration-dependent manner. Among these colon cancer cell lines, HCT116 cells were most responsive while HT29 cells were the least responsive to ethanol-stimulated cell migration/invasion. These in vitro results were supported by animal studies which demonstrated that ethanol enhanced the metastasis of colorectal cancer cells to the liver and lung. Monocyte chemoattractant protein-1 (MCP-1) is a chemokine that plays an important role in regulating tumor microenvironment and metastasis. Alcohol increased the expression of MCP-1 and its receptor CCR2 at both protein and mRNA levels. The pattern of alcohol-induced alterations in MCP-1 expression was consistent with its effect on migration/invasion; HCT116 cells displayed the highest up-regulation of MCP-1/CCR2 in response to alcohol exposure. An antagonist of CCR2 blocked alcohol-stimulated migration. Alcohol caused an initial cytosolic accumulation of ß-catenin and its subsequent nuclear translocation by inhibiting GSK3ß activity. Alcohol stimulated the activity of MCP-1 gene promoter in a ß-catenin-dependent manner. Furthermore, knock-down of MCP-1/CCR2 or ß-catenin was sufficient to inhibit alcohol-induced cell migration/invasion. Together, these results suggested that alcohol may promote the metastasis of CRC through modulating GSK3ß/ß-catenin/MCP-1 pathway.

CD151-α3ß1 integrin complexes are prognostic markers of glioblastoma and cooperate with EGFR to drive tumor cell motility and invasion.

Glioblastoma, one of the most aggressive forms of brain cancer, is featured by high tumor cell motility and invasiveness, which not only fuel tumor infiltration, but also enable escape from surgical or other clinical interventions. Thus, better understanding of how these malignant traits are controlled will be key to the discovery of novel biomarkers and therapies against this deadly disease. Tetraspanin CD151 and its associated α3ß1 integrin have been implicated in facilitating tumor progression across multiple cancer types. How these adhesion molecules are involved in the progression of glioblastoma, however, remains largely unclear. Here, we examined an in-house tissue microarray-based cohort of 96 patient biopsies and TCGA dataset to evaluate the clinical significance of CD151 and α3ß1 integrin. Functional and signaling analyses were also conducted to understand how these molecules promote the aggressiveness of glioblastoma at molecular and cellular levels. Results from our analyses showed that CD151 and α3 integrin were significantly elevated in glioblastomas at both protein and mRNA levels, and exhibited strong inverse correlation with patient survival (p < 0.006). These adhesion molecules also formed tight protein complexes and synergized with EGF/EGFR to accelerate tumor cell motility and invasion. Furthermore, disruption of such complexes enhanced the survival of tumor-bearing mice in a xenograft model, and impaired activation of FAK and small GTPases. Also, knockdown- or pharmacological agent-based attenuation of EGFR, FAK or Graf (ARHGAP26)/small GTPase-mediated pathways markedly mitigated the aggressiveness of glioblastoma cells. Collectively, our findings provide clinical, molecular and cellular evidence of CD151-α3ß1 integrin complexes as promising prognostic biomarkers and therapeutic targets for glioblastoma.

Metastasis suppressor NME1 regulates melanoma cell morphology, self-adhesion and motility via induction of fibronectin expression.

Expression of the metastasis suppressor NME1 in melanoma is associated with reduced cellular motility and invasion in vitro and metastasis in vivo, but the underlying molecular mechanisms are not completely understood. Herein, we report a novel mechanism through which NME1 controls melanoma cell morphology via upregulation of the extracellular matrix (ECM) protein fibronectin. Expression of NME1 strongly suppressed cell motility in melanoma cell lines 1205LU and M14. The resulting sedentary phenotype was associated with a more flattened appearance and marked increases in actin stress fibre and focal adhesion formation. NME1-induced focal adhesions were colocalized with dense deposits of fibronectin, which were absent or minimal in the corresponding NME1-deficient parental lines. NME1 was a strong inducer of fibronectin mRNA and protein expression, shown with reciprocal approaches of forced NME1 expression and shRNA-mediated knock-down. Increased synthesis and ECM deposition of fibronectin was necessary for NME1-induced cell spreading, as knock-down of fibronectin opposed the effects of NME1 on cell morphology. Fibronectin knock-down also reversed the ability of NME1 to promote aggregation when cells were plated on a non-adherent substratum. Similarly, inhibiting activation of the fibronectin receptor integrin α4ß1 with an anti-α4 antibody reversed the motility-suppressing effect of NME1. A positive correlation was observed between NME1 and fibronectin mRNA in clinical biopsies of normal skin, benign nevi and primary melanomas, but not in metastatic forms, suggesting the NME1/fibronectin axis represents a barrier to melanoma progression. In summary, these findings indicate fibronectin is an important effector of the motility-suppressing function of NME1 in melanoma cells.

CD151 represses mammary gland development by maintaining the niches of progenitor cells.

Tetraspanin CD151 interacts with laminin-binding integrins (i.e., α3ß1, α6ß1 and α6ß4) and other cell surface molecules to control diverse cellular and physiological processes, ranging from cell adhesion, migration and survival to tissue architecture and homeostasis. Here, we report a novel role of CD151 in maintaining the branching morphogenesis and activity of progenitor cells during the pubertal development of mammary glands. In contrast to the disruption of laminin-binding integrins, CD151 removal in mice enhanced the tertiary branching in mammary glands by 2.4-fold and the number of terminal end buds (TEBs) by 30%, while having minimal influence on either primary or secondary ductal branching. Consistent with these morphological changes are the skewed distribution of basal/myoepithelial cells and a 3.2-fold increase in proliferating Ki67-positive cells. These novel observations suggest that CD151 impacts the branching morphogenesis of mammary glands by upregulating the activities of bipotent progenitor cells. Indeed, our subsequent analyses indicate that upon CD151 removal the proportion of CD24(Hi)CD49f(Low) progenitor cells in the mammary gland increased by 34%, and their proliferating and differentiating activities were significantly upregulated. Importantly, fibronectin, a pro-branching extracellular matrix (ECM) protein deposited underlying mammary epithelial or progenitor cells, increased by >7.2-fold. Moreover, there was a concomitant increase in the expression and nuclear distribution of Slug, a transcription factor implicated in the maintenance of mammary progenitor cell activities. Taken together, our studies demonstrate that integrin-associated CD151 represses mammary branching morphogenesis by controlling progenitor cell activities, ECM integrity and transcription program.

CD151-α3ß1 integrin complexes suppress ovarian tumor growth by repressing slug-mediated EMT and canonical Wnt signaling.

Human ovarian cancer is diagnosed in the late, metastatic stages but the underlying mechanisms remain poorly understood. We report a surprising functional link between CD151-α3ß1 integrin complexes and the malignancy of serous-type ovarian cancer. Analyses of clinical specimens indicate that CD151 expression is significantly reduced or diminished in 90% of metastatic lesions, while it remains detectable in 58% of primary tumors. These observations suggest a putative tumor-suppressing role of CD151 in ovarian cancer. Indeed, our analyses show that knocking down CD151 or α3 integrin enhances tumor cell proliferation, growth and ascites production in nude mice. These changes are accompanied by impaired cell-cell contacts and aberrant expression of E-cadherin, Mucin 5AC and fibronectin, largely reminiscent of an epithelial to mesenchymal transition (EMT)-like change. Importantly, Slug, a master regulator of EMT, is markedly elevated. Knocking down Slug partially restores CD151-α3ß1 integrin complex-dependent suppression of cell proliferation. Moreover, disruption of these adhesion protein complexes is accompanied by a concomitant activation of canonical Wnt signaling, including elevated levels of ß-catenin and Axin-2 as well as resistance to the inhibition in ß-catenin-dependent transcriptional complexes. Together, our study demonstrates that CD151-α3ß1 integrin complexes regulate ovarian tumor growth by repressing Slug-mediated EMT and Wnt signaling.

The deubiquitinase USP28 stabilizes LSD1 and confers stem-cell-like traits to breast cancer cells.

LSD1 is a critical chromatin modulator that controls cellular pluripotency and differentiation through the demethylation of H3K4me1/2. Overexpression of LSD1 has been observed in many types of tumors and is correlated with its oncogenic effects in tumorigenesis. However, the mechanism leading to LSD1 upregulation in tumors remains unclear. Using an unbiased siRNA screening against all the human deubiquitinases, we identified USP28 as a bona fide deubiquitinase of LSD1. USP28 interacted with and stabilized LSD1 via deubiquitination. USP28 overexpression correlated with LSD1 upregulation in multiple cancer cell lines and breast tumor samples. Knockdown of USP28 resulted in LSD1 destabilization, leading to the suppression of cancer stem cell (CSC)-like characteristics in vitro and inhibition of tumorigenicity in vivo, which can be rescued by ectopic LSD1 expression. Our study reveals a critical mechanism underlying the epigenetic regulation by USP28 and provides another treatment approach against breast cancer.

Integrin-associated CD151 drives ErbB2-evoked mammary tumor onset and metastasis.

ErbB2+ human breast cancer is a major clinical problem. Prior results have suggested that tetraspanin CD151 might contribute to ErbB2-driven breast cancer growth, survival, and metastasis. In other cancer types, CD151 sometimes supports tumor growth and metastasis. However, a definitive test of CD151 effects on de novo breast cancer initiation, growth, and metastasis has not previously been done. We used CD151 gene-deleted mice expressing the MMTV-ErbB2 transgene to show that CD151 strongly supports ErbB2+ mammary tumor initiation and metastasis. Delayed tumor onset (by 70-100 days) in the absence of CD151 was accompanied by reduced survival of mammary epithelial cells and impaired activation of FAK- and MAPK-dependent pathways. Both primary tumors and metastatic nodules showed smooth, regular borders, consistent with a less invasive phenotype. Furthermore, consistent with impaired oncogenesis and decreased metastasis, CD151-targeted MCF-10A/ErbB2 cells showed substantial decreases in three-dimensional colony formation, EGF-stimulated tumor cell motility, invasion, and transendothelial migration. These CD151-dependent functions were largely mediated through α6ß4 integrin. Moreover, CD151 ablation substantially prevented PKC- and EGFR/ERK-dependent α6ß4 integrin phosphorylation, consistent with retention of epithelial cell polarity and intermediate filament cytoskeletal connections, which helps to explain diminished metastasis. Finally, clinical data analyses revealed a strong correlation between CD151 and ErbB2 expression and metastasis-free survival of breast cancer patients. In conclusion, we provide strong evidence that CD151 collaborates with LB integrins (particularly α6ß4 and ErbB2 (and EGFR) receptors to regulate multiple signaling pathways, thereby driving mammary tumor onset, survival, and metastasis. Consequently, CD151 is a useful therapeutic target in malignant ErbB2+ breast cancer.

CD151 restricts the α6 integrin diffusion mode.

Laminin-binding integrins (α3ß1, α6ß1, α6ß4, α7ß1) are almost always expressed together with tetraspanin CD151. In every coexpressing cell analyzed to date, CD151 makes a fundamental contribution to integrin-dependent motility, invasion, morphology, adhesion and/or signaling. However, there has been minimal mechanistic insight into how CD151 affects integrin functions. In MDA-MB-231 mammary cells, tetraspanin CD151 knockdown impairs α6 integrin clustering and functions without decreasing α6 integrin expression or activation. Furthermore, CD151 knockdown minimally affects the magnitude of α6 integrin diffusion, as measured using single particle tracking. Instead, CD151 knockdown has a novel and unexpected dysregulating effect on the mode of α6 integrin diffusion. In control cells α6 integrin shows mostly random-confined diffusion (RCD) and some directed motion (DMO). In sharp contrast, in CD151-knockdown cells α6 integrin shows mostly DMO. In control cells α6 diffusion mode is sensitive to actin disruption, talin knockdown and phorbol ester stimulation. By contrast, CD151 knockdown cell α6 integrin is sensitive to actin disruption but desensitized to talin knockdown or phorbol ester stimulation, indicating dysregulation. Both phorbol ester and EGF stimulate cell spreading and promote α6 RCD in control cells. By contrast, CD151-ablated cells retain EGF effects but lose phorbol-ester-stimulated spreading and α6 RCD. For α6 integrins, physical association with CD151 promotes α6 RCD, in support of α6-mediated cable formation and adhesion. By comparison, for integrins not associated with CD151 (e.g. αv integrins), CD151 affects neither diffusion mode nor αv function. Hence, CD151 support of α6 RCD is specific and functionally relevant, and probably underlies diverse CD151 functions in skin, kidney and cancer cells.

Disruption of laminin-integrin-CD151-focal adhesion kinase axis sensitizes breast cancer cells to ErbB2 antagonists.

Resistance to anti-ErbB2 agents is a significant problem in the treatment of human ErbB2+ breast cancers. We show here that adhesion of human ErbB2+ breast cancer cells to basement membrane laminin-5 provides substantial resistance to trastuzumab and lapatinib, agents that respectively target the extracellular and kinase domains of ErbB2. Knockdown of laminin-binding integrins (alpha6beta4, alpha3beta1) or associated tetraspanin protein CD151 reversed laminin-5 resistance and sensitized ErbB2+ cells to trastuzumab and lapatinib. CD151 knockdown, together with trastuzumab treatment, inhibited ErbB2 activation and downstream signaling through Akt, Erk1/2, and focal adhesion kinase (FAK). Hence, ErbB2 function in mammary tumor cells is promoted by integrin-mediated adhesion to laminin-5, with strong support by CD151, leading to signaling through FAK. Consequently, removal or inhibition of any of these components (laminin-5, integrin, CD151, FAK) markedly sensitizes cells to anti-ErbB2 agents. These new insights should be useful when devising strategies for overcoming drug resistance in ErbB2+ cancers.

DHHC2 affects palmitoylation, stability, and functions of tetraspanins CD9 and CD151.

Although palmitoylation markedly affects tetraspanin protein biochemistry and functions, relevant palmitoylating enzymes were not known. There are 23 mammalian "DHHC" (Asp-His-His-Cys) proteins, which presumably palmitoylate different sets of protein substrates. Among DHHC proteins tested, DHHC2 best stimulated palmitoylation of tetraspanins CD9 and CD151, whereas inactive DHHC2 (containing DH-->AA or C-->S mutations within the DHHC motif) failed to promote palmitoylation. Furthermore, DHHC2 associated with CD9 and CD151, but not other cell surface proteins, and DHHC2 knockdown diminished CD9 and CD151 palmitoylation. Knockdown of six other Golgi-resident DHHC proteins (DHHC3, -4, -8, -17, -18, and -21) had no effect on CD9 or CD151. DHHC2 selectively affected tetraspanin palmitoylation, but not the palmitoylations of integrin beta4 subunit and bulk proteins visible in [(3)H]palmitate-labeled whole cell lysates. DHHC2-dependent palmitoylation also had multiple functional effects. First, it promoted physical associations between CD9 and CD151, and between alpha3 integrin and other proteins. Second, it protected CD151 and CD9 from lysosomal degradation. Third, the presence of DHHC2, but not other DHHC proteins, shifted cells away from a dispersed state and toward increased cell-cell contacts.