A molecularly engineered lectin destroys EGFR and inhibits the growth of non-small cell lung cancer.

Survival rates for non-small cell lung cancer (NSCLC) remain low despite the advent of novel therapeutics. Tyrosine kinase inhibitors (TKIs) targeting mutant epidermal growth factor receptor (EGFR) in NSCLC have significantly improved mortality but are plagued with challenges--they can only be used in the small fraction of patients who have susceptible driver mutations, and resistance inevitably develops. Aberrant glycosylation on the surface of cancer cells is an attractive therapeutic target as these abnormal glycosylation patterns are typically specific to cancer cells and are not present on healthy cells. H84T BanLec (H84T), a lectin previously engineered by our group to separate its antiviral activity from its mitogenicity, exhibits precision binding of high mannose, an abnormal glycan present on the surface of many cancer cells, including NSCLC. Here, we show that H84T binds to and inhibits the growth of diverse NSCLC cell lines by inducing lysosomal degradation of EGFR and leading to cancer cell death through autophagy. This is a mechanism distinct from EGFR TKIs and is independent of EGFR mutation status; H84T inhibited proliferation of both cell lines expressing wild type EGFR and those expressing mutant EGFR that is resistant to all TKIs. Further, H84T binds strongly to multiple and diverse clinical samples of both pulmonary adenocarcinoma and squamous cell carcinoma. H84T is thus a promising potential therapeutic in NSCLC, with the ability to circumvent the challenges currently faced by EGFR TKIs.

The UBE2F-CRL5ASB11-DIRAS2 axis is an oncogene and tumor suppressor cascade in pancreatic cancer cells.

UBE2F, a neddylation E2, neddylates CUL5 to activate cullin-RING ligase-5, upon coupling with neddylation E3 RBX2/SAG. Whether and how UBE2F controls pancreatic tumorigenesis is previously unknown. Here, we showed that UBE2F is essential for the growth of human pancreatic cancer cells with KRAS mutation. In the mouse KrasG12D pancreatic ductal adenocarcinoma (PDAC) model, Ube2f deletion suppresses cerulein-induced pancreatitis, and progression of acinar-to-ductal metaplasia (ADM) and pancreatic intraepithelial neoplasia. Mechanistically, Ube2f deletion inactivates the Mapk-c-Myc signals via blocking ubiquitylation of Diras2, a substrate of CRL5Asb11 E3 ligase. Biologically, DIRAS2 suppresses growth and survival of human pancreatic cancer cells harboring mutant KRAS, and Diras2 deletion largely rescues the phenotypes induced by Ube2f deletion. Collectively, Ube2f or Diras2 plays a tumor-promoting or tumor-suppressive role in the mouse KrasG12D PDAC model, respectively. The UBE2F-CRL5ASB11 axis could serve as a valid target for pancreatic cancer, whereas the levels of UBE2F or DIRAS2 may serve as prognostic biomarkers for PDAC patients.

Sag/Rbx2 Partial Inactivation Sensitizes Mice to Radiation and Radiation-Induced Tumorigenesis1.

SAG (sensitive to apoptosis gene)/RBX2 (RING box-2), is the second family member of RING component of cullin-RING ligase (CRL) complex required for its enzymatic activity. Using total or conditional Sag knockout mouse models, we previously showed that Sag plays an essential role in embryonic development, apoptosis, vasculogenesis, angiogenesis and tumorigenesis. We also found that Sag-null ES cells are more sensitive to radiation. In this study, we generated the SagΔ/flneo mice with partial Sag inactivation due to deletion in one allele (Δ allele), and disrupted expression in the another (by a neo cassette). Compared to wild-type, SagΔ/fl-neo mice are more sensitive to a lethal dose of radiation with significantly shortened life span, resulting from an increased tissue damage with reduced proliferation and increased apoptosis in the intestines. Similar observations were made when SagΔ/fl-neo mice received a high dose of radiation directly delivered to the abdomen with reduced proliferation and prolonged DNA damage repair. Mechanistically, we found accumulations of Sag substrates, p21 and p27, explaining the proliferation defect. Finally, we found that SagΔ/fl-neo mice are more prone to tumorigenesis induced by a low dose of radiation with shortened life-span and increased incidence of lymphoma. Collectively, our study demonstrates that Sag protects mice from radiation-induced tissue damages and tumorigenesis.

The Sag-Shoc2 axis regulates conversion of mPanINs to cystic lesions in Kras pancreatic tumor model.

SAG/RBX2 is an E3 ligase, whereas SHOC2 is a RAS-RAF positive regulator. In this study, we address how Sag-Shoc2 crosstalk regulates pancreatic tumorigenesis induced by KrasG12D. Sag deletion increases the size of pancreas and causes the conversion of murine pancreatic intraepithelial neoplasms (mPanINs) to neoplastic cystic lesions with a mechanism involving Shoc2 accumulation, suggesting that Sag determines the pathological process via targeting Shoc2. Shoc2 deletion significantly inhibits pancreas growth, mPanIN formation, and acinar cell transdifferentiation, indicating that Shoc2 is essential for KrasG12D-induced pancreatic tumorigenesis. Likewise, in a primary acinar 3D culture, Sag deletion inhibits acinar-to-ductal transdifferentiation, while Shoc2 deletion significantly reduces the duct-like structures. Mechanistically, SAG is an E3 ligase that targets SHOC2 for degradation to affect both Mapk and mTorc1 pathways. Shoc2 deletion completely rescues the phenotype of neoplastic cystic lesions induced by Sag deletion, indicating physiological relevance of the Sag-Shoc2 crosstalk. Thus, the Sag-Shoc2 axis specifies the pancreatic tumor types induced by KrasG12D.

Transgenic expression of Sag/Rbx2 E3 causes early stage tumor promotion, late stage cytogenesis and acinar loss in the Kras-PDAC model.

SAG (Sensitive to Apoptosis Gene), also known as RBX2 or ROC2, is a RING component of CRL (Cullin-RING ligase), required for its activity. Our previous studies showed that Sag/Rbx2 co-operated with Kras or Pten loss to promote tumorigenesis in the lung and prostate, respectively, but antagonized Kras to inhibit skin tumorigenesis, suggesting a tissue/context dependent function of Sag. The role of SAG in KRAS-induced pancreatic tumorigenesis is unknown. In this study, we mined a cancer database and found that SAG is overexpressed in pancreatic cancer tissues and correlates with decreased patient survival. Whether Sag overexpression plays a causal role in pancreatic tumorigenesis is unknown. Here, we reported the generation of Sag transgenic mouse model alone (CS), or in combination with KrasG12D, driven by p48-Cre (KCS mice) for pancreatic specific Sag expression. Sag transgenic expression alone has no phenotypical abnormality, but in combination with KrasG12D promotes ADM (acinar-to-ductal metaplasia) conversion in vitro and mPanIN1 formation in vivo at the early stage, and impairs pancreatic functions at the late stage, as evidenced by poor glucose tolerance and significantly reduced α-Amylase activity, and induction of cytogenesis and acinar cell loss, eventually leading to atrophic pancreata and shortened mouse life-span. Mechanistically, Sag transgenic expression altered several key signaling pathways, particularly inactivation of mTORC1 signaling due to Deptor accumulation, and activation of the antioxidant Nrf2-Nqo1 axis. Thus, Sag plays a stage dependent promotion (early) and fate-changing (late) role during Kras-pancreatic tumorigenesis, likely via regulating its key substrates, which control growth-related signal transduction pathways.

Neddylation inactivation represses androgen receptor transcription and inhibits growth, survival and invasion of prostate cancer cells.

Androgen receptor (AR) and its constitutively active variants (AR-Vs) have been extensively implicated in the progression and recurrence of prostate cancer, making them attractive targets in the treatment of this disease. Whether and how neddylation modification regulates AR, and the therapeutic implications of this potential regulation, are relatively unexplored areas of investigation. Here we report that neddylation inactivation by the pharmacological inhibitor MLN4924 or Lenti-shRNA-based genetic knockdown of neddylation activating enzyme (NAE) selectively suppressed growth and survival of prostate cancer cells with minor, if any, effect on normal prostate epithelial cells. MLN4924 also significantly suppressed the invasive capacity of prostate cancer cells. Furthermore, compared to monotherapy, the combination of MLN4924 with AR antagonist or castration significantly enhanced growth suppression of prostate cancer cells in vitro, and tumor growth in an in vivo xenograft model. Mechanistically, MLN4924 repressed the transcription of AR/AR-V7 and its downstream targets, and blocked MMP2 and MMP9 expression. Taken together, our study reveals that the neddylation pathway positively regulates AR/AR-V7 transcription, and that the neddylation inhibitor MLN4924 has therapeutic potential for the treatment of aggressive prostate cancers.

The FBXW2-MSX2-SOX2 axis regulates stem cell property and drug resistance of cancer cells.

SOX2 is a key transcription factor that plays critical roles in maintaining stem cell property and conferring drug resistance. However, the underlying mechanisms by which SOX2 level is precisely regulated remain elusive. Here we report that MLN4924, also known as pevonedistat, a small-molecule inhibitor of neddylation currently in phase II clinical trials, down-regulates SOX2 expression via causing accumulation of MSX2, a known transcription repressor of SOX2 expression. Mechanistic characterization revealed that MSX2 is a substrate of FBXW2 E3 ligase. FBXW2 binds to MSX2 and promotes MSX2 ubiquitylation and degradation. Likewise, FBXW2 overexpression shortens the protein half-life of MSX2, whereas FBXW2 knockdown extends it. We further identified hypoxia as a stress condition that induces VRK2 kinase to facilitate MSX2-FBXW2 binding and FBXW2-mediated MSX2 ubiquitylation and degradation, leading to SOX2 induction via derepression. Biologically, expression of FBXW2 or SOX2 promotes tumor sphere formation, which is blocked by MSX2 expression. By down-regulating SOX2 through inactivation of FBXW2 E3 ligase, MLN4924 sensitizes breast cancer cells to tamoxifen in both in vitro and in vivo cancer cell models. Thus, a negative cascade of the FBXW2-MSX2-SOX2 axis was established, which regulates stem cell property and drug resistance. Finally, an inverse correlation of expression was found between FBXW2 and MSX2 in lung and breast cancer tissues. Collectively, our study revealed an anticancer mechanism of MLN4924. By inactivating FBXW2, MLN4924 caused MSX2 accumulation to repress SOX2 expression, leading to suppression of stem cell property and sensitization of breast cancer cells to tamoxifen.

LSD1 destabilizes FBXW7 and abrogates FBXW7 functions independent of its demethylase activity.

FBXW7 acts as a typical tumor suppressor, with loss-of-function alterations in human cancers, by promoting ubiquitylation and degradation of many oncoproteins. Lysine-specific demethylase 1 (LSD1) is a well-characterized histone demethylase. Whether LSD1 has demethylase-independent activity remains elusive. Here we report that LSD1 directly binds to FBXW7 to destabilize FBXW7 independent of its demethylase activity. Specifically, LSD1 is a pseudosubstrate of FBXW7 and LSD1-FBXW7 binding does not trigger LSD1 ubiquitylation, but instead promotes FBXW7 self-ubiquitylation by preventing FBXW7 dimerization. The self-ubiquitylated FBXW7 is subjected to degradation by proteasome as well as lysosome in a manner dependent on autophagy protein p62/SQSTM1. Biologically, LSD1 destabilizes FBXW7 to abrogate its functions in growth suppression, nonhomologous end-joining repair, and radioprotection. Collectively, our study revealed a previously unknown activity of LSD1, which likely contributes to its oncogenic function. Targeting LSD1 protein, not only its demethylase activity, might be a unique approach for LSD1-based drug discovery for anticancer application.

Inactivation of SAG or ROC1 E3 Ligase Inhibits Growth and Survival of Renal Cell Carcinoma Cells: Effect of BIM.

SAG (Sensitive to Apoptosis Gene) and ROC1 (Regulator of Cullin-1) are two family members of the RING component of CRL (Cullin RING ligase). Both members are essential for growth and survival of several types of human cancer cells; their role in renal cell carcinoma (RCC), however, remains elusive. Here we reported that compared to adjacent normal tissues, both SAG and ROC1 are overexpressed in RCC, which is positively correlated with poor patient survival, particularly for SAG. Depletion of SAG or ROC1 inhibited growth and survival of RCC cells by inducing G2/M arrest, senescence, and apoptosis likely due to accumulation of WEE1, p21, p27, NOXA, and BIM. Interestingly, simultaneous BIM knockdown in RCC cells partially rescues growth suppression triggered by depletion of SAG, but not ROC1, suggesting a differential role of BIM. Collectively, our study provides the proof-of-concept evidence that RING components of CRL are attractive candidates for targeted therapy of RCC.

Neddylation inhibitor MLN4924 suppresses cilia formation by modulating AKT1.

The primary cilium is a microtubule-based sensory organelle. The molecular mechanism that regulates ciliary dynamics remains elusive. Here, we report an unexpected finding that MLN4924, a small molecule inhibitor of NEDD8-activating enzyme (NAE), blocks primary ciliary formation by inhibiting synthesis/assembly and promoting disassembly. This is mainly mediated by MLN4924-induced phosphorylation of AKT1 at Ser473 under serum-starved, ciliary-promoting conditions. Indeed, pharmaceutical inhibition (by MK2206) or genetic depletion (via siRNA) of AKT1 rescues MLN4924 effect, indicating its causal role. Interestingly, pAKT1-Ser473 activity regulates both ciliary synthesis/assembly and disassembly in a MLN4924 dependent manner, whereas pAKT-Thr308 determines the ciliary length in MLN4924-independent but VHL-dependent manner. Finally, MLN4924 inhibits mouse hair regrowth, a process requires ciliogenesis. Collectively, our study demonstrates an unexpected role of a neddylation inhibitor in regulation of ciliogenesis via AKT1, and provides a proof-of-concept for potential utility of MLN4924 in the treatment of human diseases associated with abnormal ciliogenesis.

FBXW2 suppresses migration and invasion of lung cancer cells via promoting ß-catenin ubiquitylation and degradation.

FBXW2 inhibits proliferation of lung cancer cells by targeting SKP2 for degradation. Whether and how FBXW2 regulates tumor invasion and metastasis is previously unknown. Here, we report that FBXW2 is an E3 ligase for ß-catenin. FBXW2 binds to ß-catenin upon EGF-AKT1-mediated phosphorylation on Ser552, and promotes its ubiquitylation and degradation. FBXW2 overexpression reduces ß-catenin levels and protein half-life, whereas FBXW2 knockdown increases ß-catenin levels, protein half-life and transcriptional activity. Functionally, FBXW2 overexpression inhibits migration and invasion by blocking transactivation of MMPs driven by ß-catenin, whereas FXBW2 knockdown promotes migration, invasion and metastasis both in vitro and in vivo lung cancer models. In human lung cancer specimens, while FBXW2 levels are inversely correlated with ß-catenin levels and lymph-node metastasis, lower FBXW2 coupled with higher ß-catenin, predict a worse patient survival. Collectively, our study demonstrates that FBXW2 inhibits tumor migration, invasion and metastasis in lung cancer cells by targeting ß-catenin for degradation.

The FBXW7-SHOC2-Raptor Axis Controls the Cross-Talks between the RAS-ERK and mTORC1 Signaling Pathways.

FBXW7 is a tumor suppressive E3 ligase, whereas RAS-ERK and mechanistic target of rapamycin kinase (mTORC1) are two major oncogenic pathways. Whether and how FBXW7 regulates these two oncogenic pathways are unknown. Here, we showed that SHOC2, a RAS activator, is a FBXW7 substrate. Growth stimuli trigger SHOC2 phosphorylation on Thr507 by the mitogen-activated protein kinase (MAPK) signal, which facilitates FBXW7 binding for ubiquitylation and degradation. FBXW7-mediated SHOC2 degradation terminates the RAS-MAPK signals and inhibits proliferation. Furthermore, SHOC2 selectively binds to Raptor to competitively inhibit the Raptor-mTOR binding to inactivate mTORC1 and induce autophagy, whereas Raptor binding of SHOC2 inhibits the SHOC2-RAS binding to block the MAPK pathway and proliferation. Finally, SHOC2 is overexpressed in pancreatic cancer, which correlated with poor patient survival. SHOC2 mutations were found in lung cancer tissues with gain-of-function activity. Collectively, the SHOC2-Raptor interaction triggers negative cross-talk between RAS-ERK and mTORC1 pathways, whereas FBXW7 regulates both pathways by targeting SHOC2 for ubiquitylation and degradation.

Inhibiting neddylation modification alters mitochondrial morphology and reprograms energy metabolism in cancer cells.

Abnormal activation of neddylation modification and dysregulated energy metabolism are frequently seen in many types of cancer cells. Whether and how neddylation modification affects cellular metabolism remains largely unknown. Here, we showed that MLN4924, a small-molecule inhibitor of neddylation modification, induces mitochondrial fission-to-fusion conversion in breast cancer cells via inhibiting ubiquitylation and degradation of fusion-promoting protein mitofusin 1 (MFN1) by SCFß-TrCP E3 ligase and blocking the mitochondrial translocation of fusion-inhibiting protein DRP1. Importantly, MLN4924-induced mitochondrial fusion is independent of cell cycle progression, but confers cellular survival. Mass-spectrometry-based metabolic profiling and mitochondrial functional assays reveal that MLN4924 inhibits the TCA cycle but promotes mitochondrial OXPHOS. MLN4924 also increases glycolysis by activating PKM2 via promoting its tetramerization. Biologically, MLN4924 coupled with the OXPHOS inhibitor metformin, or the glycolysis inhibitor shikonin, significantly inhibits cancer cell growth both in vitro and in vivo. Together, our study links neddylation modification and energy metabolism, and provides sound strategies for effective combined cancer therapies.

SAG/RBX2 E3 Ubiquitin Ligase Differentially Regulates Inflammatory Responses of Myeloid Cell Subsets.

Macrophages form an important component of the innate immune system and serve as first responders against invading pathogens. While pathways critical for initiation of inflammatory responses between macrophages and other LysM+ myeloid cells are largely similar, it remains unknown whether a specific pathway has differential effects on inflammatory responses mediated between these cells. Recent studies demonstrated that depletion of SAG (Sensitive to Apoptosis Gene), an E3 ubiquitin ligase, blocked inflammatory responses generated by macrophages and dendritic cells in response to LPS in cell culture settings. However, the in vivo role of Sag on modulation of macrophages and neutrophil is not known. Here we generated LysM-Cre/Sagfl/fl mice with selective Sag deletion in myeloid lineage, and found that in contrast to in vitro observations, LysM-Cre/Sagfl/fl mice showed increased serum levels of proinflammatory cytokines and enhanced mortality in response to LPS. Interestingly, while Sag-/- macrophages released less proinflammatory cytokines, Sag-/- neutrophils released more. Mechanistically, expression of a list of genes response to LPS was significantly altered in bone marrow cells from LysM-Cre+/Sagfl/fl mice after LPS challenge. Specifically, induction by LPS of myeloperoxidase (Mpo), a key neutrophil enzyme, and Elane, neutrophil expressed elastase, was significantly decreased upon Sag depletion. Collectively, our study revealed that Sag plays a differential role in the activation of macrophages and neutrophils.

MicroRNA-34a Attenuates Metastasis and Chemoresistance of Bladder Cancer Cells by Targeting the TCF1/LEF1 Axis.

BACKGROUND/AIMS: Chemoresistance is largely responsible for relapses of bladder cancer during clinical therapy. However, the molecular mechanisms involved in the chemoresistance of bladder cancer are unclear. Growing evidence supports the theory that microRNAs (miRNAs) play an important role in chemotherapeutic drug resistance because they are downregulated in many malignancies that have been implicated in the regulation of diverse processes in cancer cells. More specifically, the extent and precise mechanism of the involvement of miR-34as in chemoresistance to epirubicin (EPI) in the treatment of bladder cancer remains unclear. METHODS: In this study, real-time quantitative polymerase chain reaction (PCR) was used to analyze the expression of miR-34a in bladder cancer cell line BIU87 and its EPI chemoresistant cell line BIU87/ADR. The miR-34a profiles in bladder cancer tissues were obtained from The Cancer Genome Atlas database. The effect of miR-34a on chemosensitivity was evaluated by cell viability assays, colony formation assays, and in vivo experimentation. Apoptosis and the cell cycle were examined by flow cytometry. A luciferase reporter assay was used to assess the target genes of miR-34a. Western blot and qPCR were used to analyze the expression of target proteins and downstream molecules. RESULTS: The downregulation of miR-34a in bladder cancer serves as an independent predictor of reduced patient survival. The CCK-8 assay showed that miR-34a overexpression resulted in increased sensitivity to EPI, while miR-34a downregulation resulted in chemoresistance to EPI in vitro. Moreover, it was found that miR-34a increased the sensitivity of BIU87/ADR cells to chemotherapy in vivo. The luciferase reporter assay ascertained that TCF1 and LEF1 are direct target genes of miR-34a. It was found that miR-34a increased chemosensitivity in BIU87/ADR cells by inhibiting the TCF1/LEF1 axis. CONCLUSIONS: The results of this study indicate that miR-34a contributes to the chemosensitivity of BIU87/ADR by inhibiting the TCF1/LEF1 axis. Consequently, miR-34a is a determinant of BIU87 chemosensitivity and may therefore serve as a potential therapeutic target in bladder cancer treatment.

UBE2M Is a Stress-Inducible Dual E2 for Neddylation and Ubiquitylation that Promotes Targeted Degradation of UBE2F.

UBE2M and UBE2F are two family members of neddylation E2 conjugating enzyme that, together with E3s, activate CRLs (Cullin-RING Ligases) by catalyzing cullin neddylation. However, whether and how two E2s cross-talk with each other are largely unknown. Here, we report that UBE2M is a stress-inducible gene subjected to cis-transactivation by HIF-1 and AP1, and MLN4924, a small molecule inhibitor of E1 NEDD8-activating enzyme (NAE), upregulates UBE2M via blocking degradation of HIF-1α and c-JUN. UBE2M is a dual E2 for targeted ubiquitylation and degradation of UBE2F, acting as a neddylation E2 to activate CUL3-Keap1 E3 under physiological conditions but as a ubiquitylation E2 for Parkin-DJ-1 E3 under stressed conditions. UBE2M-induced UBE2F degradation leads to CRL5 inactivation and subsequent NOXA accumulation to suppress the growth of lung cancer cells. Collectively, our study establishes a negative regulatory axis between two neddylation E2s with UBE2M ubiquitylating UBE2F, and two CRLs with CRL3 inactivating CRL5.

Increased Piezo1 channel activity in interstitial Cajal-like cells induces bladder hyperactivity by functionally interacting with NCX1 in rats with cyclophosphamide-induced cystitis.

The Piezo1 channel is a mechanotransduction mediator, and Piezo1 abnormalities have been linked to several clinical disorders. However, the role of the Piezo1 channel in cystitis-associated bladder dysfunction has not been documented. The current study aimed to discover the functional role of this channel in regulating bladder activity during cyclophosphamide (CYP)-induced cystitis. One hundred four female rats were randomly assigned to the control, CYP-4h, CYP-48h and CYP-8d groups. CYP successfully induced acute or chronic cystitis in these rats. CYP treatment for 48h or 8d significantly increased Piezo1 channel expression in bladder interstitial Cajal-like cells (ICC-LCs), and the increase in CYP-8d rats was more prominent. In addition, 2.5 µM Grammostola spatulata mechanotoxin 4 (GsMTx4) significantly attenuated bladder hyperactivity in CYP-8d rats by inhibiting the Piezo1 channel in bladder ICC-LCs. Furthermore, by using GsMTx4 and siRNA targeting the Piezo1 channel, we demonstrated that hypotonic stress-induced Piezo1 channel activation significantly triggered Ca2+ and Na+ influx into bladder ICC-LCs during CYP-induced chronic cystitis. In addition, the Piezo1 channel functionally interacted with the relatively activated reverse mode of Na+/Ca2+ exchanger 1 (NCX1) in bladder ICC-LCs from CYP-8d rats. In conclusion, we suggest that the functional role of the Piezo1 channel in CYP-induced chronic cystitis is based on its synergistic effects with NCX1, which can significantly enhance [Ca2+]i and result in Ca2+ overload in bladder ICC-LCs, indicating that the Piezo1 channel and NCX1 are potential novel therapeutic targets for chronic cystitis-associated bladder hyperactivity.

Inactivation of ribosomal protein S27-like confers radiosensitivity via the Mdm2-p53 and Mdm2-MRN-ATM axes.

RPS27L (ribosomal protein S27-like) is an evolutionarily conserved ribosomal protein and a direct p53 target. We recently reported that Rps27l disruption triggers ribosomal stress to induce p53, causing postnatal death, which can be rescued by Trp53 +/- . Whether and how Rps27l modulates radiosensitivity is unknown. Here we report that Rps27l -/- ; Trp53 +/- mice are extremely sensitive to radiation due to reduced proliferation and massive induction of apoptosis in radiation-sensitive organs. Mechanistically, the radiation sensitivity is mediated by two signaling pathways: (1) activated p53 pathway due to imbalanced Mdm2/Mdm4 levels and reduced E3 ligase activity; and (2) reduced DNA damage response due to reduced MRN/Atm signal as a result of elevated Mdm2 binding of Nbs1 to inhibit Nbs1-Atm binding and subsequent Atm activation. Indeed, heterozygous deletion of Mdm2 restores the MRN/Atm signal. Collectively, our study revealed a physiological condition under which Rps27l regulates the Mdm2/p53 and MRN/Atm axes to maintain DNA damage response and to confer radioprotection in vivo.

Interleukin-6/signal transducer and activator of transcription 3 promotes prostate cancer resistance to androgen deprivation therapy via regulating pituitary tumor transforming gene 1 expression.

Prostate cancer can progress from androgen dependence to androgen deprivation resistance with some unknown mechanisms. The current study aims to explore the possible role of pituitary tumor transforming gene1 (PTTG1) in castration-resistant prostate cancer (CRPC). Initially, we found that PTTG1 expression was significantly increased in androgen-independent prostate cancer cell lines PC3, DU145 and CRPC specimens compared with that in androgen-dependent prostate cancer cell line LNCaP and initial prostate cancer specimens. PTTG1 overexpression significantly enhanced the cell survival rate, clonality and tumorigenicity in LNCaP cells upon androgen-deprivation therapy (ADT). While knockdown of PTTG1 expression significantly elevated the sensitivity of DU145 cells to ADT. The effects of PTTG1 overexpression on LNCaP cells may be ascribed to the induced EMT and increased CD44+ CD24- cancer stem cell population. Furthermore, we detected that PTTG1 expression was regulated by interleukin-6 via activated signal transducer and activator of transcription 3 (STAT3) directly binding to the region -500 to +1 of PTTG1 promoter in LNCaP cells. In conclusion, our results elucidate that interleukin-6/STAT3 activation can increase PTTG1 expression and, consequently, promote the resistance to ADT in CRPC by inducing EMT and increasing the cancer stem cell population, suggesting that PTTG1 may be a novel therapeutic target for CRPC.

The ß-TrCP-FBXW2-SKP2 axis regulates lung cancer cell growth with FBXW2 acting as a tumour suppressor.

ß-TrCP and SKP2 are two well-studied F-box proteins, which often act as oncogenes. Whether and how they communicate with each other is unknown. Here we report that FBXW2, a poorly characterized F-box, is a substrate of ß-TrCP1 and an E3 ligase for SKP2. While ß-TrCP1 promotes FBXW2 ubiquitylation and shortens its half-life, FBXW2 does the same to SKP2. FBXW2 has tumour suppressor activity against lung cancer cells and blocks oncogenic function of both ß-TrCP1 and SKP2. The levels of ß-TrCP1-FBXW2-SKP2 are inversely correlated during cell cycle with FBXW2 and ß-TrCP/SKP2 being high or low, respectively, in arrested cells, whereas the opposite is true in proliferating cells. Consistently, FBXW2 predicts a better patient survival, whereas ß-TrCP1 and SKP2 predict a worse survival. Finally, the gain- and loss-of-function mutations of FBXW2 are found in various human cancers. Collectively, our data show that the ß-TrCP-FBXW2-SKP2 axis forms an oncogene-tumour suppressor-oncogene cascade to control cancer cell growth with FBXW2 acting as a tumour suppressor by promoting SKP2 degradation.