Special issue "The advance of solid tumor research in China": Discoidin domain receptor 2 promotes colorectal cancer metastasis by regulating epithelial mesenchymal transition via activating AKT signaling.

Tumor metastasis is one of the main reasons for the high mortality rate associated with colorectal cancer (CRC). However, its underlying mechanisms have not been fully understood. Here, we reported that the expression of discoidin domain receptor 2 (DDR2) was significantly upregulated in CRC tissues compared to that in normal adjacent tissues. The expression level of DDR2 was negatively associated with prognosis of CRC patients. Therefore, DDR2 may play an oncogenic role in CRC development. Furthermore, DDR2 induced epithelial mesenchymal transition in CRC cells and regulated their invasive and metastatic capacity in vitro and in vivo. Mechanistically, increased DDR2 expression level activated the AKT/GSK-3ß/Slug signaling pathway. In conclusion, these findings showed that DDR2 promoted CRC metastasis and DDR2 inhibition might represent an effective therapeutic strategy for local advanced and metastatic CRC treatment.

DDR1 functions as an immune negative factor in colorectal cancer by regulating tumor-infiltrating T cells through IL-18.

Immunotherapies represented by programmed cell death protein 1/programmed cell death ligand 1 (PD-1/PD-L1) immune checkpoint inhibitors have made great progress in the field of anticancer treatment, but most colorectal cancer patients do not benefit from immunotherapy. Discoidin domain receptor 1 (DDR1), a tyrosine kinase receptor, is activated by collagen binding and overexpressed in various malignancies. However, the role of DDR1 in colorectal cancer and immunoregulation remains unclear. In this study, we found DDR1 is highly expressed in colorectal cancer tissues and negatively associated with patient survival. We demonstrated that DDR1 promotes colorectal tumor growth only in vivo. Mechanistically, DDR1 is a negative immunomodulator in colorectal cancer and is involved in low infiltration of CD4+ and CD8+ T cells by inhibiting IL-18 synthesis. We also reported that DDR1 enhances the expression of PD-L1 through activating the c-Jun amino terminal kinase (JNK) signaling pathway. In conclusion, our findings elucidate the immunosuppressive role of DDR1 in colorectal cancer, which may represent a novel target to enhance the efficacy of immunotherapy in colorectal cancer.

Discoidin domain receptors orchestrate cancer progression: A focus on cancer therapies.

Discoidin domain receptors (DDR), including DDR1 and DDR2, are special types of the transmembrane receptor tyrosine kinase superfamily. DDR are activated by binding to the triple-helical collagen and, in turn, DDR can activate signal transduction pathways that regulate cell-collagen interactions involved in multiple physiological and pathological processes such as cell proliferation, migration, apoptosis, and cytokine secretion. Recently, DDR have been found to contribute to various diseases, including cancer. In addition, aberrant expressions of DDR have been reported in various human cancers, which indicates that DDR1 and DDR2 could be new targets for cancer treatment. Considerable effort has been made to design DDR inhibitors and several molecules have shown therapeutic effects in pre-clinical models. In this article, we review the recent literature on the role of DDR in cancer progression, the development status of DDR inhibitors, and the clinical potential of targeting DDR in cancer therapies.

Cyclin-dependent kinase 1-mediated AMPK phosphorylation regulates chromosome alignment and mitotic progression.

AMP-activated protein kinase (AMPK), a heterotrimeric serine/threonine kinase and cellular metabolic sensor, has been found to regulate cell cycle checkpoints in cancer cells in response to energetic stress, to harmonize proliferation with energy availability. Despite AMPK's emergent association with the cell cycle, it still has not been fully delineated how AMPK is regulated by upstream signaling pathways during mitosis. We report, for the first time, direct CDK1 phosphorylation of both the catalytic α1 and α2 subunits, as well as the ß1 regulatory subunit, of AMPK in mitosis. We found that AMPK-knockout U2OS osteosarcoma cells have reduced mitotic indexes and that CDK1 phosphorylation-null AMPK is unable to rescue the phenotype, demonstrating a role for CDK1 regulation of mitotic entry through AMPK. Our results also denote a vital role for AMPK in promoting proper chromosomal alignment, as loss of AMPK activity leads to misaligned chromosomes and concomitant metaphase delay. Importantly, AMPK expression and activity was found to be critical for paclitaxel chemosensitivity in breast cancer cells and positively correlated with relapse-free survival in systemically treated breast cancer patients.

Zyxin promotes colon cancer tumorigenesis in a mitotic phosphorylation-dependent manner and through CDK8-mediated YAP activation.

Zyxin is a member of the focal adhesion complex and plays a critical role in actin filament polymerization and cell motility. Several recent studies showed that Zyxin is a positive regulator of Yki/YAP (Yes-associated protein) signaling. However, little is known about the mechanisms by which Zyxin itself is regulated and how Zyxin affects Hippo-YAP activity. We first showed that Zyxin is phosphorylated by CDK1 during mitosis. Depletion of Zyxin resulted in significantly impaired colon cancer cell proliferation, migration, anchorage-independent growth, and tumor formation in xenograft animal models. Mitotic phosphorylation is required for Zyxin activity in promoting growth. Zyxin regulates YAP activity through the colon cancer oncogene CDK8. CDK8 knockout phenocopied Zyxin knockdown in colon cancer cells, while ectopic expression of CDK8 substantially restored the tumorigenic defects of Zyxin-depletion cells. Mechanistically, we showed that CDK8 directly phosphorylated YAP and promoted its activation. Fully activated YAP is required to support the growth in CDK8-knockout colon cancer cells in vitro and in vivo. Together, these observations suggest that Zyxin promotes colon cancer tumorigenesis in a mitotic-phosphorylation-dependent manner and through CDK8-mediated YAP activation.

Cyclin-dependent kinase 1 (CDK1)-mediated mitotic phosphorylation of the transcriptional co-repressor Vgll4 inhibits its tumor-suppressing activity.

The Hippo pathway is an evolutionarily conserved signaling pathway that plays important roles in stem cell biology, tissue homeostasis, and cancer development. Vestigial-like 4 (Vgll4) functions as a transcriptional co-repressor in the Hippo-Yes-associated protein (YAP) pathway. Vgll4 inhibits cell proliferation and tumor growth by competing with YAP for binding to TEA-domain proteins (TEADs). However, the mechanisms by which Vgll4 itself is regulated are unclear. Here we identified a mechanism that regulates Vgll4's tumor-suppressing function. We found that Vgll4 is phosphorylated in vitro and in vivo by cyclin-dependent kinase 1 (CDK1) during antimitotic drug-induced mitotic arrest and also in normal mitosis. We further identified Ser-58, Ser-155, Thr-159, and Ser-280 as the main mitotic phosphorylation sites in Vgll4. We also noted that the nonphosphorylatable mutant Vgll4-4A (S58A/S155A/T159A/S280A) suppressed tumorigenesis in pancreatic cancer cells in vitro and in vivo to a greater extent than did wild-type Vgll4, suggesting that mitotic phosphorylation inhibits Vgll4's tumor-suppressive activity. Consistent with these observations, the Vgll4-4A mutant possessed higher-binding affinity to TEAD1 than wild-type Vgll4. Interestingly, Vgll4 and Vgll4-4A markedly suppressed YAP and ß-catenin signaling activity. Together, these findings reveal a previously unrecognized mechanism for Vgll4 regulation in mitosis and its role in tumorigenesis.

Next-generation sequencing identifies CDKN2A alterations as prognostic biomarkers in recurrent or metastatic head and neck squamous cell carcinoma predominantly receiving immune checkpoint inhibitors.

Background: This study aimed to identify potential biomarkers in patients with recurrent or metastatic head and neck squamous cell carcinoma (HNSCC) and further probe the prognostic implications of CDKN2A mutations, particularly within a subset receiving immunotherapy. Methods: In this retrospective single-center study, we evaluated the next-generation sequencing (NGS) data from Foundation Medicine (FM) for patients with recurrent or metastatic HNSCC between January 1, 2019, and December 31, 2021. Patients were stratified based on CDKN2A loss-of-function (LOF) versus wild-type (WT) categorizations, with a focused subgroup analysis on those administered immunotherapy. Results: The study encompassed 77 patients, of which 62 had undergone immunotherapy. The median duration of follow-up was 22.6 months. For the CDKN2A LOF group, the median overall survival (OS) was 16.5 months, contrasted with 30.0 months in the CDKN2A WT group (P=0.014). Notably, female gender (hazard ratio [HR]=4.526, 95% confidence interval [CI]: 1.934-10.180, P=0.0003) and CDKN2A LOF (HR=2.311, 95% CI: 1.156-4.748, P=0.019) emerged as independent risk factors for mortality in patients with recurrent or metastatic HNSCC. Within the immunotherapy subset, the median OS was 11.7 months for the CDKN2A LOF group, and 22.5 months for the CDKN2A WT group (P=0.017). Further, the female gender (HR=4.022, 95% CI: 1.417-10.710, P=0.006), CDKN2A LOF (HR=4.389, 95% CI: 1.782-11.460, P=0.002), and a combined positive score below 1 (HR=17.20, 95% CI: 4.134-79.550, P<0.0001) were identified as significant predictors of mortality among patients with recurrent or metastatic HNSCC receiving immunotherapy. Conclusion: Alterations manifesting as LOF in the CDKN2A gene stand as robust indicators of unfavorable survival outcomes in HNSCC patients, including the subset that underwent immunotherapy.

mPEG-PDLLA Micelles Potentiate Docetaxel for Intraperitoneal Chemotherapy in Ovarian Cancer Peritoneal Metastasis.

Ovarian cancer is the second most common cause of gynecological cancer death in women. It is usually diagnosed late and accompanied by peritoneal metastasis. For ovarian cancer with peritoneal metastasis, intraperitoneal (IP) chemotherapy can maintain a high drug concentration in the abdominal cavity and reduce local and systemic toxicity. Recently, docetaxel (DTX) has shown broad-spectrum antitumor activity against various malignant tumors, including ovarian cancer with peritoneal metastasis. However, DTX has limited clinical applications due to its poor water solubility, predisposition to hypersensitivity, fluid retention, and varying degrees of neurotoxicity. In this study, we prepared methoxy-poly(ethylene glycol)-block-poly(D,L-lactide) (mPEG-PDLLA) micelles loaded with DTX and developed an alternative, less toxic, more effective DTX formulation, without Tween 80, and evaluated its pharmacokinetics in the abdominal cavity and its efficacy in ovarian cancer with peritoneal metastasis. The mean diameter of DTX-mPEG-PDLLA was about 25 nm, and the pharmacokinetics of BALB/c mice via IP showed that the plasma exposure of DTX-mPEG-PDLLA was about four times lower than that of DTX. Importantly, DTX-mPEG-PDLLA was significantly more effective than DTX and prolonged the survival period in a SKOV-3 ovarian cancer peritoneal metastasis model. Moreover, the apoptosis rate was significantly increased in vitro. Based on these findings, it is expected that DTX-mPEG-PDLLA can enhance efficacy against ovarian cancer peritoneal metastasis, while reducing toxic side effects, and has the potential to be used in the clinical treatment of peritoneal metastatic cancer.

MARK2 regulates chemotherapeutic responses through class IIa HDAC-YAP axis in pancreatic cancer.

Despite paclitaxel's wide use in cancer treatment, patient response rate is still low and drug resistance is a major clinical obstacle. Through a Phos-tag-based kinome-wide screen, we identified MARK2 as a critical regulator for paclitaxel chemosensitivity in PDAC. We show that MARK2 is phosphorylated by CDK1 in response to antitubulin chemotherapeutics and in unperturbed mitosis. Phosphorylation is essential for MARK2 in regulating mitotic progression and paclitaxel cytotoxicity in PDAC cells. Mechanistically, our findings also suggest that MARK2 controls paclitaxel chemosensitivity by regulating class IIa HDACs. MARK2 directly phosphorylates HDAC4 specifically during antitubulin treatment. Phosphorylated HDAC4 promotes YAP activation and controls expression of YAP target genes induced by paclitaxel. Importantly, combination of HDAC inhibition and paclitaxel overcomes chemoresistance in organoid culture and preclinical PDAC animal models. The expression levels of MARK2, HDACs, and YAP are upregulated and positively correlated in PDAC patients. Inhibition of MARK2 or class IIa HDACs potentiates paclitaxel cytotoxicity by inducing mitotic abnormalities in PDAC cells. Together, our findings identify the MARK2-HDAC axis as a druggable target for overcoming chemoresistance in PDAC.

LIMD1 phosphorylation in mitosis is required for mitotic progression and its tumor-suppressing activity.

LIM domains containing 1 (LIMD1) is a member of the Zyxin family proteins and functions as a tumor suppressor in lung cancer. LIMD1 has been shown to regulate Hippo-YAP signaling activity. Here, we report a novel regulatory mechanism for LIMD1. We found that cyclin-dependent kinase 1 (CDK1) and c-Jun NH2-terminal kinases 1/2 (JNK1/2) phosphorylate LIMD1 in vitro and in cells during anti-tubulin drug-induced mitotic arrest. Phosphorylation also occurs during normal mitosis. S272, S277, S421, and S424 were identified as the main phosphorylation sites in LIMD1. Deletion of LIMD1 resulted in a shortened mitotic cell cycle and phosphorylation of LIMD1 is required for proper mitotic progression. We further showed that the phosphorylation-deficient mutant LIMD1-4A is less active in suppressing cell proliferation, anchorage-independent growth, cell migration, and invasion in lung cancer cells. Together, our findings suggest that LIMD1 is a key regulator of mitotic progression, and that dysregulation of LIMD1 contributes to tumorigenesis.

Cyclin-dependent kinase 1-mediated phosphorylation of YES links mitotic arrest and apoptosis during antitubulin chemotherapy.

YES is a member of the SRC family kinase (SFK) group of non-receptor tyrosine kinases, which are implicated in multiple key cellular processes involved in oncogenesis. Antitubulin agents have been widely used as chemotherapeutics for cancer patients and these drugs arrest cells in mitosis, leading to subsequent cell death. In the present study, we define a mechanism for phospho-regulation of YES that is critical for its role in response to antitubulin agents. Specifically, we found that YES is phosphorylated at multiple sites on its N-terminal unique domain by the cell cycle kinase CDK1 during antitubulin drug-induced mitotic arrest. Phosphorylation of YES occurs during normal mitosis. Deletion of YES causes arrest in prometaphase and polyploidy in a p53-independent manner. We further show that YES regulates antitubulin chemosensitivity. Importantly, mitotic phosphorylation is essential for these effects. In support of our findings, we found that YES expression is high in recurrent ovarian cancer patients. Finally, through expression profiling, we documented that YES phosphorylation affects expression of multiple cell cycle regulators. Collectively, our results reveal a previously unrecognized mechanism for controlling the activity of YES during antitubulin chemotherapeutic treatment and suggest YES as a potential target for the treatment of antitubulin-resistant cancer.

CDK1-mediated mitotic phosphorylation of PBK is involved in cytokinesis and inhibits its oncogenic activity.

PDZ-binding kinase (PBK) plays a major role in proliferation and in safeguarding mitotic fidelity in cancer cells. Frequently upregulated in many cancers, PBK drives tumorigenesis and metastasis. PBK has been shown to be phosphorylated in mitosis by cyclin-dependent kinase 1 (CDK1)/cyclin B, however, no studies have been done examining PBK mitotic phosphorylation in oncogenesis. Additionally to the previously identified Threonine-9 phosphorylation, we found that Threonine-24, Serine-32, and Serine-59 of PBK are also phosphorylated. PBK is phosphorylated in vitro and in cells by CDK1 during antimitotic drug-induced mitotic arrest and in normal mitosis. We demonstrated that mitotic phosphorylation of Threonine-9 is involved in cytokinesis. The non-phosphorylatable mutant PBK-T9A augments tumorigenesis to a greater extent than wild type PBK in breast cancer cells, suggesting that PBK mitotic phosphorylation inhibits its tumor promoting activity. The PBK-T9A mutant also transforms and increases the proliferation of immortalized breast epithelial cells. Collectively, this study reveals that CDK1-mediated mitotic phosphorylation of PBK is involved in cytokinesis and inhibits its oncogenic activity.