The expression and role of tyrosine kinase ETK/BMX in renal cell carcinoma

Bioinformatic Analysis Reveals Bone Marrow Kinase as a Potential Diagnostic and Prognostic Biomarker for Multiple Cancer Types

INTRODUCTION

Bone marrow kinase, or BMX, is alternatively referred to as endothelial tyrosine kinase (Etk). It plays a vital role in the processes of cell proliferation, survival, immune activation, and the modulation of diverse signaling pathways. Since there are few direct comprehensive studies linking BMX role with multiple cancers, this study aimed to utilize bioinformatic tools to conduct a comprehensive analysis of BMX across multiple cancers, assessing its potential role.

METHODS

Multiple databases including the Tumor Immune Estimation Resource (TIMER), Gene Expression Profiling Interactive Analysis (GEPIA), and University of Alabama at Birmingham Cancer Data Analysis Portal (UALCAN), have been used to explore BMX expression across different cancers, which has been further validated by using Gene Expression Omnibus (GEO) public datasets. In addition, we used the Kaplan-Meier plotter to estimate overall survival and cBioPortal for genetic alterations analysis. This study accommodates several other analyses like clinical parameters, immune cell infiltration, and DNA promoter methylation profiles to evaluate the general role of BMX in several cancers.  Results: The present investigation revealed that the BMX gene expression was significantly downregulated and could serve as an effective diagnostic biomarker in five types of cancers, namely breast invasive carcinoma (BRCA), colon adenocarcinoma (COAD), lung adenocarcinoma (LUAD), lung squamous cell carcinoma (LUSC), and rectum adenocarcinoma (READ) (all p < 0.05). Detailed analyses revealed notable downregulation of BMX in various clinical parameters such as age, gender, race, and cancer stage (all p < 0.05). To better understand the immunotherapeutic role of BMX, this investigation further examined the immune infiltration which exhibited positive correlations between BMX expression and the infiltration of immunological cells such as B cells, CD8+ T cells, CD4+ T cells, macrophages, neutrophils, and dendritic cells, especially in COAD, LUAD, and LUSC (all p < 0.05). In addition, the present study has demonstrated that diminished BMX gene expression is correlated with an unfavorable prognosis in kidney renal clear cell carcinoma (KIRC), liver hepatocellular carcinoma (LIHC), sarcoma (SARC), and uterine corpus endometrial carcinoma (UCEC); thus BMX gene expression can be used as a prognostic target for these specific cancers. Also, the results showed that the promoter methylation level of BMX was significantly elevated in LUAD and LUSC, whereas it was significantly decreased in BRCA (all p < 0.001). Importantly, our findings of significantly low BMX expression in LUAD and LUSC, along with their methylation profiles suggest that the low expression of BMX across these cancers is due to epigenetic factors. However, genetic alteration analysis revealed that mutations existed in only approximately 2% of the TCGA samples.

CONCLUSION

Our study revealed BMX as a diagnostic biomarker in BRCA, COAD, LUAD, LUSC, and READ and a prognostic biomarker in KIRC, LIHC, SARC, and UCEC. Furthermore, epigenetic variables may have a greater impact on BMX expression levels especially in LUAD and LUSC. This study also emphasized the role of BMX in the infiltration of immune cells, such as B cells, CD8+ T cells, CD4+ T cells, macrophages, neutrophils, and dendritic cells, in certain cancers. The BMX expression level highlights the prognostic value and potential therapeutic potential of BMX.

Preclinical spheroid models identify BMX as a therapeutic target for metastatic MYCN nonamplified neuroblastoma

The development of targeted therapies offers new hope for patients affected by incurable cancer. However, multiple challenges persist, notably in controlling tumor cell plasticity in patients with refractory and metastatic illness. Neuroblastoma (NB) is an aggressive pediatric malignancy originating from defective differentiation of neural crest-derived progenitors with oncogenic activity due to genetic and epigenetic alterations and remains a clinical challenge for high-risk patients. To identify critical genes driving NB aggressiveness, we performed combined chromatin and transcriptome analyses on matched patient-derived xenografts (PDXs), spheroids, and differentiated adherent cultures derived from metastatic MYCN nonamplified tumors. Bone marrow kinase on chromosome X (BMX) was identified among the most differentially regulated genes in PDXs and spheroids versus adherent models. BMX expression correlated with high tumor stage and poor patient survival and was crucial to the maintenance of the self-renewal and tumorigenic potential of NB spheroids. Moreover, BMX expression positively correlated with the mesenchymal NB cell phenotype, previously associated with increased chemoresistance. Finally, BMX inhibitors readily reversed this cellular state, increased the sensitivity of NB spheroids toward chemotherapy, and partially reduced tumor growth in a preclinical NB model. Altogether, our study identifies BMX as a promising innovative therapeutic target for patients with high-risk MYCN nonamplified NB.

TRIM26 inhibits clear cell renal cell carcinoma progression through destabilizing ETK and thus inactivation of AKT/mTOR signaling

BACKGROUND

Tripartite motif-containing 26 (TRIM26), a member of the TRIM protein family, exerts dual function in several types of cancer. Nevertheless, the precise role of TRIM26 in clear cell renal cell carcinoma (ccRCC) has not been investigated.

METHODS

The expression of TRIM26 in ccRCC tissues and cell lines were examined through the use of public resources and experimental validation. The impacts of TRIM26 on cell proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT) process were determined via CCK-8, colony formation, EdU incorporation, wound healing, Transwell invasion, Western blot, and Immunofluorescence assays. RNA-seq followed by bioinformatic analyses were used to identify the downstream pathway of TRIM26. The interaction between TRIM26 and ETK was assessed by co-immunoprecipitation, qRT-PCR, Western blot, cycloheximide (CHX) chase, and in vivo ubiquitination assays.

RESULTS

We have shown that TRIM26 exhibits a downregulation in both ccRCC tissues and cell lines. Furthermore, this decreased expression of TRIM26 is closely linked to unfavorable overall survival and diseases-free survival outcomes among ccRCC patients. Gain- and loss-of-function experiments demonstrated that increasing the expression of TRIM26 suppressed the proliferation, migration, invasion, and EMT process of ccRCC cells. Conversely, reducing the expression of TRIM26 had the opposite effects. RNA sequencing, coupled with bioinformatic analysis, revealed a significant enrichment of the mTOR signaling pathway in the control group compared to the group with TRIM26 overexpression. This finding was then confirmed by a western blot assay. Subsequent examination revealed that TRMI26 had a direct interaction with ETK, a non-receptor tyrosine kinase. This interaction facilitated the ubiquitination and degradation of ETK, resulting in the deactivation of the AKT/mTOR signaling pathway in ccRCC. ETK overexpression counteracted the inhibitory effects of TRIM26 overexpression on cell proliferation, migration, and invasion.

CONCLUSION

Our results have shown a novel mechanism by which TRIM26 hinders the advancement of ccRCC by binding to and destabilizing ETK, thus leading to the deactivation of AKT/mTOR signaling. TRIM26 shows promise as both a therapeutic target and prognostic biomarker for ccRCC patients.

Ibrutinib combination therapy for advanced gastrointestinal and genitourinary tumours: results from a phase 1b/2 study

BACKGROUND

Ibrutinib, a first-in-class inhibitor of Bruton's tyrosine kinase, is approved for the treatment of various B-cell malignancies and chronic graft-versus-host disease. Based on encouraging preclinical data, safety and efficacy of ibrutinib combined with companion drugs for advanced renal cell carcinoma (RCC), gastric/gastroesophageal junctional adenocarcinoma (GC), and colorectal adenocarcinoma (CRC) were evaluated.

METHODS

Ibrutinib 560 mg or 840 mg once daily was administered with standard doses of everolimus for RCC, docetaxel for GC, and cetuximab for CRC. Endpoints included determination of the recommended phase 2 dose (RP2D) of ibrutinib in phase 1b and efficacy (overall response rate [ORR] for GC and CRC; progression-free survival [PFS] for CRC) in phase 2.

RESULTS

A total of 39 (RCC), 46 (GC), and 50 (RCC) patients were enrolled and received the RP2D. Safety profiles were consistent with the individual agents used in the study. Confirmed ORRs were 3% (RCC), 21% (GC), and 19% (CRC). Median (90% CI) PFS was 5.6 (3.9-7.5) months in RCC, 4.0 (2.7-4.2) months in GC, and 5.4 (4.1-5.8) months in CRC.

CONCLUSIONS

Clinically meaningful increases in efficacy were not observed compared to historical controls; however, the data may warrant further evaluation of ibrutinib combinations in other solid tumours.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02599324.

Phase Ib/II trial of Ibrutinib and Nivolumab in Patients with Advanced Refractory Renal Cell Carcinoma1

BACKGROUND: Although immune checkpoint inhibitor-based therapy has improved the outcomes of many patients with metastatic renal cell carcinoma (mRCC), most eventually develop disease progression. Newer agents that modulate immune response can possibly potentiate checkpoint inhibitor therapy. The ITK/ETK/BTK inhibitor ibrutinib has been reported to inhibit myeloid derived suppressor cells in preclinical models and to potentiate immunotherapy. We conducted an investigator-initiated trial of ibrutinib plus the PD1 inhibitor nivolumab in mRCC patients, particularly in those previously exposed to immune checkpoint inhibitors. METHODS: Eligible patients had mRCC of any histologic subtype, completed at least one line of prior systemic therapy which could have included prior immunotherapy, and had acceptable end-organ function with ECOG performance status of 0–2. Treatment consisted of nivolumab 240 mg intravenously every 2 weeks plus ibrutinib 560 mg (dose level 0) or 420 mg (dose level -1) orally once daily. Cycle length was 28 days. Dose limiting toxicity (DLT) was defined as any Grade 3 or higher adverse event (AE) attributable to therapy. After identification of the recommended phase 2 dose (RP2D), up to 19 patients were enrolled to an expansion cohort to further evaluate toxicities and any early evidence of efficacy. The primary endpoints of the trial were establishment of RP2D and progression-free survival (PFS). RESULTS: A total of 31 patients were enrolled, 6 to dose level 0, 7 (of which one was not evaluable for DLT) in dose level -1, and 18 in the expansion cohort. Median age was 60 years (range, 36–90), most had clear cell histology (n = 27; 87%), and most had prior immune checkpoint inhibitor therapy (n = 28; 90%). Three patients experienced one DLT each, all in dose level 0 (all Grade 3), namely elevated lipase, hypoalbuminemia, and nausea. No DLTs were seen in dose level –1 which was declared the RP2D. The most common Grade 3 or higher AEs include anemia (n = 5), lymphocyte count decrease (4), nausea (2), and hypotension (2). Of 28 patients evaluable for response, one patient (3.6%) had a complete response, 2 (7.1%) had a partial response, and 11 (39.2%) had stable disease, for an objective response rate of 10.7%(95%CI: 3.7%–27.2%) and a disease control rate of 50%(95%CI: 32.6%–67.4%). All responders had received prior immune checkpoint inhibitor therapy. Median PFS was 2.5 months (95%CI, 1.9 –4.8) while median OS was 9.1 months (95%CI, 6.6 –19.0). CONCLUSIONS: Ibrutinib at a dose of 420 mg orally once daily in combination with nivolumab 240 mg IV every 2 weeks is feasible and tolerable in mRCC patients. No unique immune-related AEs were observed. Anti-tumor activity was seen in patients previously exposed to PD-1 targeted therapy.

Effect of ciRS-7 expression on clear cell renal cell carcinoma progression

Background

Circular RNA ciRS-7 has been reported to be involved in the progression of various cancers. However, ciRS-7 expression and its role in clear cell renal cell carcinoma (ccRCC) progression remains unclear. This study aimed to investigate the effect of ciRS-7 expression on ccRCC and the related signaling pathway.

Methods

ciRS-7 expression was analyzed using quantitative reverse transcription polymerase chain reaction in 87 pairs of ccRCC and matched adjacent normal tissues. The role of ciRS-7 in ccRCC cell proliferation and invasion was determined using the cell counting kit-8 and invasion assays, respectively. Potential mechanisms underlying the role of ciRS-7 in promoting ccRCC progression were explored by Western blotting. The relationship between the expression of ciRS-7 and features of ccRCC was analyzed by the Chi-square test and progression-free survival was determined using a Kaplan-Meier plot.

Results

ciRS-7 was overexpressed in ccRCC tissues compared with that in matched adjacent normal tissues. In addition, ciRS-7 up-regulation was closely associated with tumor diameter (P = 0.050), clinical stage (P = 0.009), and distant metastasis (P = 0.007). ciRS-7 knockdown in 786O and 769P cells markedly inhibited their proliferative and invasive abilities. In addition, ciRS-7 inhibition reduced phosphorylated epidermal growth factor receptor (p-EGFR) and phosphorylated serine/threonine kinase (p-Akt) levels.

Conclusions

ciRS-7 up-regulation could promote ccRCC cell proliferation and invasion, which may be related with the EGFR/Akt signaling pathway. ciRS-7 might be a potential ccRCC therapeutic target.

The RUFYs, a Family of Effector Proteins Involved in Intracellular Trafficking and Cytoskeleton Dynamics

Intracellular trafficking is essential for cell structure and function. In order to perform key tasks such as phagocytosis, secretion or migration, cells must coordinate their intracellular trafficking, and cytoskeleton dynamics. This relies on certain classes of proteins endowed with specialized and conserved domains that bridge membranes with effector proteins. Of particular interest are proteins capable of interacting with membrane subdomains enriched in specific phosphatidylinositol lipids, tightly regulated by various kinases and phosphatases. Here, we focus on the poorly studied RUFY family of adaptor proteins, characterized by a RUN domain, which interacts with small GTP-binding proteins, and a FYVE domain, involved in the recognition of phosphatidylinositol 3-phosphate. We report recent findings on this protein family that regulates endosomal trafficking, cell migration and upon dysfunction, can lead to severe pathology at the organismal level.

Drug resistance in papillary RCC: from putative mechanisms to clinical practicalities

Papillary renal cell carcinoma (pRCC) is the second most common renal cell carcinoma (RCC) subtype and accounts for 10-15% of all RCCs. Despite clinical need, few pharmacogenomics studies in pRCC have been performed. Moreover, current research fails to adequately include pRCC laboratory models, such as the ACHN or Caki-2 pRCC cell lines. The molecular mechanisms involved in pRCC development and drug resistance are more diverse than in clear-cell RCC, in which inactivation of VHL occurs in the majority of tumours. Drug resistance to multiple therapies in pRCC occurs via genetic alteration (such as mutations resulting in abnormal receptor tyrosine kinase activation or RALBP1 inhibition), dysregulation of signalling pathways (such as GSK3β-EIF4EBP1, PI3K-AKT and the MAPK or interleukin signalling pathways), deregulation of cellular processes (such as resistance to apoptosis or epithelial-to-mesenchymal transition) and interactions between the cell and its environment (for example, through activation of matrix metalloproteinases). Improved understanding of resistance mechanisms will facilitate drug discovery and provide new effective therapies. Further studies on novel resistance biomarkers are needed to improve patient prognosis and stratification as well as drug development.

Hypoxia-induced upregulation of BMX kinase mediates therapeutic resistance in acute myeloid leukemia

Oncogenic addiction to the Fms-like tyrosine kinase 3 (FLT3) is a hallmark of acute myeloid leukemia (AML) that harbors the FLT3-internal tandem duplication (FLT3-ITD) mutation. While FLT3 inhibitors like sorafenib show initial therapeutic efficacy, resistance rapidly develops through mechanisms that are incompletely understood. Here, we used RNA-Seq-based analysis of patient leukemic cells and found that upregulation of the Tec family kinase BMX occurs during sorafenib resistance. This upregulation was recapitulated in an in vivo murine FLT3-ITD-positive (FLT3-ITD+) model of sorafenib resistance. Mechanistically, the antiangiogenic effects of sorafenib led to increased bone marrow hypoxia, which contributed to HIF-dependent BMX upregulation. In in vitro experiments, hypoxia-dependent BMX upregulation was observed in both AML and non-AML cell lines. Functional studies in human FLT3-ITD+ cell lines showed that BMX is part of a compensatory signaling mechanism that promotes AML cell survival during FLT3 inhibition. Taken together, our results demonstrate that hypoxia-dependent upregulation of BMX contributes to therapeutic resistance through a compensatory prosurvival signaling mechanism. These results also reveal the role of off-target drug effects on tumor microenvironment and development of acquired drug resistance. We propose that the bone marrow niche can be altered by anticancer therapeutics, resulting in drug resistance through cell-nonautonomous microenvironment-dependent effects.

Etk Interaction with PFKFB4 Modulates Chemoresistance of Small-cell Lung Cancer by Regulating Autophagy

Purpose: Epithelial and endothelial tyrosine kinase (Etk), also known as bone marrow X kinase (Bmx), was found to be critical in modulating the chemoresistance of small-cell lung cancer (SCLC) in our preliminary study. However, the molecular mechanisms of Etk in SCLC chemoresistance remain poorly understood.Experimental Design: We determined correlation of Etk with autophagy in SCLC. And direct inhibition of autophagy was performed to validate its effect on chemoresistance. Coimmunoprecipitation (co-IP) and GST-pull down experiments were conducted to verify the interaction of Etk and PFKFB4, after a microarray analysis. In vitro and in vivo gain or loss-of-function analyses and evaluation of PFKFB4 expression in SCLC specimens, were done to validate its role in chemoresistance. Ibrutinib was administrated in SCLC cells to verify its synergistic anti-tumor effect with chemotherapy using preclinical models including a PDX model.Results: Downregulation of Etk suppressed autophagy in chemoresistant SCLC cells, and direct inhibition of autophagy sensitized cells to chemotherapy. PFKFB4 (6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 4) was identified as a downstream target of Etk and an Etk-interacting protein, which promoted chemoresistance in SCLC and was associated with poor therapeutic response and prognosis. Furthermore, ibrutinib was found to exhibit a synergistic anti-tumor effect with chemotherapy in targeting Etk.Conclusions: Our results demonstrated for the first time that Etk interacts with PFKFB4 to promote SCLC chemoresistance through regulation of autophagy. Aberrant Etk and PFKFB4 can be predictive factors for the chemotherapy response as well as potential therapeutic targets in SCLC. Clin Cancer Res; 24(4); 950-62. ©2017 AACR.

Bruton's tyrosine kinase (BTK) as a promising target in solid tumors

Bruton's tyrosine kinase (BTK) is a non-receptor intracellular kinase that belongs to the TEC-family tyrosine kinases together with bone marrow-expressed kinase (BMX), redundant-resting lymphocyte kinase (RLK), and IL-2 inducible T-Cell kinase (ITK). All these proteins play a key role in the intracellular signaling of both B and T lymphocytes. Recently, some preclinical data have demonstrated that BTK is present in certain tumor subtypes and in other relevant cells that are contributing to the tumor microenvironment such as dendritic cells, macrophages, myeloid derived suppressor cells and endothelial cells. Ibrutinib (PCI-32765) is an orally available small molecule that acts as an inhibitor of the BTK and is approved for the treatment of patients with some hematological malignancies. It has been suggested that ibrutinib may also have a potential antitumor activity in solid neoplasms. In this sense, ibrutinib has the ability to revert polarization of TCD4+ to Th1 lymphocytes to increase the cytotoxic ability of T CD8+ and to regulate tumor-induced immune tolerance by acting over tumor infiltrating cells activity and immunosuppressive cytokines release. Furthermore, based on its molecular activity and safety, ibrutinib has been considered as a partner for treatment combination with PI3K/AKT/mTOR inhibitors or with immune-checkpoint inhibitors, inhibiting immunosuppressive signals from the tumor microenvironment, and overcoming the immune resistance to current anti-PD1/PDL1 immunotherapeutic drugs by the CXCR4/CXCL2 pathway regulation. Currently, a broad range of different studies are evaluating the activity of ibrutinib either as single agent or in combination in patients with solid tumors.

Overexpression of G6PD Represents a Potential Prognostic Factor in Clear Cell Renal Cell Carcinoma

Glucose-6-phosphate dehydrogenase (G6PD) participates in glucose metabolism and it acts as the rate-limiting enzyme of the pentose phosphate pathway (PPP). Recently, G6PD dysregulation has been found in a variety of human cancers. Through analyzing published data in The Cancer Genome Atlas (TCGA), our pilot study indicated that G6PD mRNA expression was significantly higher in advanced Fuhrman grade in clear cell renal cell carcinoma (ccRCC). These clues promoted us to further evaluate the expression profile of G6PD and its prognostic impact in patients with ccRCC. In this study, G6PD expression levels were analyzed in 149 human ccRCC and normal tissues using immunohistochemistry. The results showed that compared with that in the normal renal samples, G6PD was found highly expressed in 51.0% of ccRCC (p<0.05). High expression of G6PD was significantly correlated to tumor extent, lymph node metastasis, Fuhrman grade, and TNM stage of ccRCC (all p<0.05). Moreover, positive G6PD expression was associated with poorer overall survival in ccRCC (p<0.001). In Cox regression analyses, high expression of G6PD also could be an independent prognostic factor for overall survival in ccRCC (p=0.007). This study suggests that overexpression of G6PD is associated with advanced disease status and therefore may become an important prognosticator for poor outcomes in ccRCC, as well as a potential therapeutic target for developing effective treatment modalities.

Discovery of 2-((3-Acrylamido-4-methylphenyl)amino)-N-(2-methyl-5-(3,4,5-trimethoxybenzamido)phenyl)-4-(methylamino)pyrimidine-5-carboxamide (CHMFL-BMX-078) as a Highly Potent and Selective Type II Irreversible Bone Marrow Kinase in the X Chromosome (BMX) Kinase Inhibitor

BMX is a member of TEC family nonreceptor tyrosine kinase and is involved in a variety of critical physiological and pathological processes. Through combination of irreversible inhibitor design and type II inhibitor design approaches, we have discovered a highly selective and potent type II irreversible BMX kinase inhibitor compound 41 (CHMFL-BMX-078), which exhibited an IC₅₀ of 11 nM by formation of a covalent bond with cysteine 496 residue in the DFG-out inactive conformation of BMX. It displayed a high selectivity profile (S score(1) = 0.01) against the 468 kinases/mutants in the KINOMEscan evaluation and achieved at least 40-fold selectivity over BTK kinase. Given the fact that BMX mediated signaling pathway is still not fully understood, compound 41 would serve as a useful pharmacological tool to elucidate the detailed mechanism of BMX mediated signaling pathways.

Vasculogenic Mimicry in Prostate Cancer: The Roles of EphA2 and PI3K

BACKGROUND. Aggressive tumor cells can form perfusable networks that mimic normal vasculature and enhance tumor growth and metastasis. A number of molecular players have been implicated in such vasculogenic mimicry, among them the receptor tyrosine kinase EphA2, which is aberrantly expressed in aggressive tumors. Here we study the role and regulation of EphA2 in vasculogenic mimicry in prostate cancer where this phenomenon is still poorly understood.

METHODS. Vasculogenic mimicry was characterized by tubules whose cellular lining was negative for the endothelial cell marker CD34 but positive for periodic acid-Schiff staining, and/or contained red blood cells. Vasculogenic mimicry was assessed in 92 clinical samples of prostate cancer and analyzed in more detail in three prostate cancer cell lines kept in three-dimensional culture. Tissue samples and cell lines were also assessed for total and phosphorylated levels of EphA2 and its potential regulator, Phosphoinositide 3-Kinase (PI3K). In addition, the role of EphA2 in vasculogenic mimicry and in cell migration and invasion were investigated by manipulating the levels of EphA2 through specific siRNAs. Furthermore, the role of PI3K in vasculogenic mimicry and in regulating EphA2 was tested by application of an inhibitor, LY294002.

RESULTS. Immunohistochemistry of prostate cancers showed a significant correlation between vasculogenic mimicry and high expression levels of EphA2, high Gleason scores, advanced TNM stage, and the presence of lymph node and distant metastases. Likewise, two prostate cancer cell lines (PC3 and DU-145) formed vasculogenic networks on Matrigel and expressed high EphA2 levels, while one line (LNCaP) showed no vasculogenic networks and lower EphA2 levels. Specific silencing of EphA2 in PC3 and DU-145 cells decreased vasculogenic mimicry as well as cell migration and invasion. Furthermore, high expression levels of PI3K and EphA2 phosphorylation at Ser897 significantly correlated with the presence of vasculogenic mimicry and in vitro inhibition of PI3K by LY294002 disrupted vasculogenic mimicry, potentially through a reduction of EphA2 phosphorylation at Ser897.

CONCLUSIONS. The expression levels of PI3K and EphA2 are positively correlated with vasculogenic mimicry both in vivo and in vitro. Moreover, phosphorylation levels of EphA2 regulated by PI3K are also significantly associated with vasculogenic mimicry in vivo. Based on its functional implication in vasculogenic mimicry in vitro, EphA2 signaling may be a potential therapeutic target in advanced prostate cancer.

CMTM4 is frequently downregulated and functions as a tumour suppressor in clear cell renal cell carcinoma

BACKGROUND

Chemokine-like factor (CKLF)-like MARVEL transmembrane domain-containing family (CMTM) is a gene family involved in multiple malignancies. CMTM4 is a member of this family and is located at chromosome 16q22.1, a locus that harbours a number of tumour suppressor genes. It has been defined as a regulator of cell cycle and division in HeLa cells; however, its roles in tumourigenesis remain poorly studied.

METHODS

An integrated bioinformatics analysis based on the array data from the GEO database was conducted to view the differential expression of CMTM4 across multiple cancers and their corresponding control tissues. Primary clear cell renal cell carcinoma (ccRCC) and the paired adjacent non-tumour tissues were then collected to examine the expression of CMTM4 by western blotting, immunohistochemistry, and quantitative RT-PCR. The ccRCC cell lines A498 and 786-O and the normal renal tubular epithelial cell line HK-2 were also tested for CMTM4 expression by western blotting. Cell Counting Kit-8 (CCK-8) and viable cell counting assays were used to delineate the growth curves of 786-O cells after CMTM4 overexpression or knockdown. Wound healing and transwell assays were performed to assess the cells' ability to migrate. The effects of CMTM4 on cellular apoptosis and cell cycle progression were analysed by flow cytometry, and cell cycle hallmarks were detected by western blotting and RT-PCR. The xenograft model in nude mice was used to elucidate the function of CMTM4 in tumourigenesis ex vivo.

RESULTS

By omic data analysis, we found a substantial downregulation of CMTM4 in ccRCC. Western blotting then confirmed that CMTM4 was dramatically reduced in 86.9 % (53/61) of ccRCC tissues compared with the paired adjacent non-tumour tissues, as well as in the 786-O and A498 ccRCC cell lines. Restoration of CMTM4 significantly suppressed 786-O cell growth by inducing G2/M cell cycle arrest and p21 upregulation, and cell migration was also inhibited. However, knockdown of CMTM4 led to a completely opposite effect on these cell behaviours. Overexpression of CMTM4 also markedly inhibited the tumour xenograft growth in nude mice.

CONCLUSIONS

CMTM4 is downregulated and exhibits tumour-suppressor activities in ccRCC, and could be exploited as a target for ccRCC treatment.

BMX Negatively Regulates BAK Function, Thereby Increasing Apoptotic Resistance to Chemotherapeutic Drugs

The ability of chemotherapeutic agents to induce apoptosis, predominantly via the mitochondrial (intrinsic) apoptotic pathway, is thought to be a major determinant of the sensitivity of a given cancer to treatment. Intrinsic apoptosis, regulated by the BCL2 family, integrates diverse apoptotic signals to determine cell death commitment and then activates the nodal effector protein BAK to initiate the apoptotic cascade. In this study, we identified the tyrosine kinase BMX as a direct negative regulator of BAK function. BMX associates with BAK in viable cells and is the first kinase to phosphorylate the key tyrosine residue needed to maintain BAK in an inactive conformation. Importantly, elevated BMX expression prevents BAK activation in tumor cells treated with chemotherapeutic agents and is associated with increased resistance to apoptosis and decreased patient survival. Accordingly, BMX expression was elevated in prostate, breast, and colon cancers compared with normal tissue, including in aggressive triple-negative breast cancers where BMX overexpression may be a novel biomarker. Furthermore, BMX silencing potentiated BAK activation, rendering tumor cells hypersensitive to otherwise sublethal doses of clinically relevant chemotherapeutic agents. Our finding that BMX directly inhibits a core component of the intrinsic apoptosis machinery opens opportunities to improve the efficacy of existing chemotherapy by potentiating BAK-driven cell death in cancer cells.

Matrix metalloproteinase-9 is required for vasculogenic mimicry by clear cell renal carcinoma cells

BACKGROUND

Vasculogenic mimicry (VM), a new pattern of tumor microcirculation system, has been proved to be important for tumor growth and progression and may be one of the causes of antiangiogenesis resistance. Matrix metalloproteinase-9 (MMP9) was shown to correlate with VM formation in some other cancers. However, the relationship between VM formation and MMP9 in renal cell carcinoma (RCC) has not been determined.

METHODS

The VM formation and MMP9 expressions were analyzed by CD34/periodic acid-Schiff dual staining and immunohistochemistry in 119 RCC specimens. We used a well-established 3-dimention culture model to compare VM formation in 786-O, 769-P, and HK-2 cell lines in vitro. MMP9 expressions on either messenger RNA or protein levels were compared among the cell lines by quantitative polymerase chain reaction or Western blot. To determine further the relationship between MMP9 and VM in RCC, 786-O and 769-P were treated with specific MMP9 inhibitor or small interfering RNA. VM formation, cell migration, and invasion were subsequently assessed by 3-dimention culture, wound-healing, and transwell assays.

RESULTS

Immunohistochemistry demonstrated both VM formation and MMP9 overexpression were positively associated with clinical staging, pathological grade, and metastasis (P<0.01). VM formation was closely correlated with MMP9 overexpression in RCC (r = 0.602, P<0.01). Lower MMP9 expression level was observed in normal kidney cell line HK-2, which was unable to form VM on Matrigel, whereas higher expression of MMP9 was found in VM-forming cancer cell lines 786-O and 769-P. Inhibition of MMP9 not only disrupted VM formation in 786-O and 769-P but also reduced cell migration and invasion.

CONCLUSIONS

These results indicate an intimate relationship between MMP9 overexpression and VM formation in RCC. Treatments targeting VM formation by inhibiting the activity of MMP9 could be beneficial in RCC therapy.