Summary
The von Hippel-Lindau tumor-suppressor gene (VHL) is lost in most clear cell renal cell carcinomas (ccRCC). Here, using human ccRCC specimens, VHL-deficient cells, and xenograft models, we show that miR-204 is a VHL-regulated tumor suppressor acting by inhibiting macroautophagy, with MAP1LC3B (LC3B) as a direct and functional target. Importantly, higher tumor grade of human ccRCC was correlated with a concomitant decrease in miR-204 and increase in LC3B levels, indicating that LC3B-mediated macroautophagy is necessary for RCC progression. VHL, in addition to inducing endogenous miR-204, triggered the expression of LC3C, an HIF-regulated LC3B paralog, that suppressed tumor growth. These data reveal a function of VHL as a tumor suppressing regulator of autophagic programs.
Summary
Autophagy promotes tumor growth by generating nutrients from the degradation of intracellular structures. Here we establish, using shRNAs, a dominant negative mutant, and a pharmacologic inhibitor, mefenamic acid (MFA), that the Transient Receptor Potential Melastatin 3 (TRPM3) channel promotes growth of clear cell renal cell carcinoma (ccRCC) and stimulates MAP1LC3A (LC3A) and MAP1LC3B (LC3B) autophagy. Increased expression of TRPM3 in RCC leads to Ca2+ influx, activation of CAMKK2, AMPK, and ULK1, and phagophore formation. In addition, TRPM3 Ca2+ and Zn2+ fluxes inhibit miR-214 which directly targets LC3A and LC3B. The von Hippel-Lindau tumor suppressor (VHL) represses TRPM3 through miR-204 directly and indirectly through another miR-204 target, Caveolin 1 (CAV1).
Von Hippel-Lindau tumor suppressor (VHL) is lost in the majority of clear cell renal cell carcinomas (ccRCC). Folliculin (FLCN) is a tumor suppressor whose function is lost in Birt-Hogg-Dubé syndrome (BHD), a disorder characterized by renal cancer of multiple histological types including clear cell carcinoma, cutaneous fibrofolliculoma, and pneumothorax. Here we explored whether there is connection between VHL and FLCN in clear cell renal carcinoma cell lines and tumors. We demonstrate that VHL regulates expression of FLCN at the mRNA and protein levels in RCC cell lines, and that FLCN protein expression is decreased in human ccRCC tumors with VHL loss, as compared with matched normal kidney tissue. Knockdown of FLCN results in increased formation of tumors by RCC cells with wild-type VHL in orthotopic xenografts in nude mice, an indication that FLCN plays a role in the tumor-suppressing activity of VHL. Interestingly, FLCN, similarly to VHL, is necessary for the activity of LC3C-mediated autophagic program that we have previously characterized as contributing to the tumor suppressing activity of VHL. The results show the existence of functional crosstalk between two major tumor suppressors in renal cancer, VHL and FLCN, converging on regulation of autophagy.
MicroRNAs (miRs) are small noncoding RNAs that play a critical role in gene regulation. Recently, traces of cancer-related miRs have been identified in body fluids, which make them remarkable noninvasive biomarkers. In this study, a new nanopore-based detection scheme utilizing a borosilicate micropipette and an assay of complementary γ-peptide nucleic acid (γ-PNA) probes conjugated to polystyrene beads have been reported for the detection of miR-204 and miR-210 related to the clear cell Renal Cell Carcinoma (ccRCC). Electroosmotic flow (EOF) is induced as the driving force to transport PNA-beads harboring target miRs to the tip of the pore (sensing zone), which results in pore blockades with unique and easily distinguishable serrated shape electrical signals. The concentration detection limit is investigated to be 1 and 10 fM for miR-204 and miR-210, respectively. The EOF transport mechanism enables highly sensitive detection of molecules with low surface charge density with 97.6% detection accuracy compared to the conventional electrophoretically driven methods. Furthermore, resistive-pulse experiments are conducted to study the correlation of the particles' surface charge density with their translocation time and verify the detection principle.
SUMMARY
Genetic S6K1 inactivation can induce apoptosis in PTEN-deficient cells. We analyzed the therapeutic potential of S6K1 inhibitors in PTEN-deficient T cell leukemia and glioblastoma. Results revealed that the S6K1 inhibitor LY-2779964 was relatively ineffective as a single agent, while S6K1-targeting AD80 induced cytotoxicity selectively in PTEN-deficient cells. In vivo, AD80 rescued 50% of mice transplanted with PTEN-deficient leukemia cells. Cells surviving LY-2779964 treatment exhibited inhibitor-induced S6K1 phosphorylation due to increased mTOR-S6K1 co-association, which primed rapid recovery of S6K1 signaling. In contrast, AD80 avoided S6K1 phosphorylation and mTOR co-association, resulting in durable suppression of S6K1-induced signaling and protein synthesis. Kinome analysis revealed that AD80 coordinately inhibits S6K1 together with the TAM family tyrosine kinase AXL. TAM suppression by BMS-777607 or genetic knockdown potentiated cytotoxic responses to LY-2779964 in PTEN-deficient glioblastoma cells. These results reveal that combination targeting of S6K1 and TAMs is a potential strategy for treatment of PTEN-deficient malignancy.
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