ABSTRACT
Targeting metabolic remodeling represents a potentially promising strategy for hepatocellular carcinoma (HCC) therapy. In-depth understanding on the regulation of the glutamine transporter alanine-serine-cysteine transporter 2 (ASCT2) contributes to the development of novel promising therapeutics. As a developmentally regulated RNA binding protein, RBM45 is capable to shuttle between nucleus and cytoplasm, and directly interacts with proteins. By bioinformatics analysis, we screened out that RBM45 was elevated in the HCC patient specimens and positively correlated with poor prognosis. RBM45 promoted cell proliferation, boosted xenograft tumorigenicity and accelerated HCC progression. Using untargeted metabolomics, it was found that RBM45 interfered with glutamine metabolism. Further results demonstrated that RBM45 positively associated with ASCT2 in human and mouse specimens. Moreover, RBM45 enhanced ASCT2 protein stability by counteracting autophagy-independent lysosomal degradation. Significantly, wild-type ASCT2, instead of phospho-defective mutants, rescued siRBM45-suppressed HCC cell proliferation. Using molecular docking approaches, we found AG-221, a mutant isocitrate dehydrogenase 2 (mIDH2) inhibitor for acute myeloid leukemia therapy, pharmacologically perturbed RBM45-ASCT2 interaction, decreased ASCT2 stability and suppressed HCC progression. These findings provide evidence that RBM45 plays a crucial role in HCC progression via interacting with and counteracting the degradation of ASCT2. Our findings suggest a novel alternative structural sites for the design of ASCT2 inhibitors and the agents interfering with RBM45-ASCT2 interaction may be a potential direction for HCC drug development.
ABSTRACT
Purpose: Orphan GPCRs (GPRs) play important roles in the malignant progression of cancer and have the potential to develop into anti-tumor drug targets. However, the biological processes and molecular mechanisms of GPR27 have not been properly assessed in cancer. Our objective was to reveal the effect of GPR27 on the progression of hepatocellular carcinoma (HCC). Methods: GPR27 levels were detected in HCC cell lines using quantitative reverse transcriptase-polymerase chain reaction and Western blot analysis. Next, the changes of phenotypes after GPR27 knockdown or overexpression were evaluated using in vitro methods. Finally, the mechanism of GPR27 in HCC was tested using RNA-seq and in vivo mouse xenograft model. Results: In the present study, we reported that suppression of GPR27 expression inhibited proliferation, colony formation, cell viability, and induced cell S phase arrest of HCC cells, whereas GPR27 overexpression led to the opposite outcomes. Moreover, suppression of GPR27 expression resulted in blocking MAPK/ERK signal pathway which indicated the inhibition of HCC cells proliferation. Further study in vivo confirmed that GPR27 can affect the proliferation of HCC cells through the MAPK/ERK pathway. Conclusion: Taken together, the findings of the present study uncover biological functions of GPR27 in HCC cells, and delineate preliminary molecular mechanisms of GPR27 in modulating HCC development and progression.
ABSTRACT
Sepiapterin reductase plays an enzymatic role in the biosynthesis of tetrahydrobiopterin, which is reported in limited studies to regulate the progression of several tumors. However, the role of sepiapterin reductase in hepatocellular carcinoma remains largely unknown. Here, we found that sepiapterin reductase was frequently highly expressed in human hepatocellular carcinoma, which was significantly associated with higher T stage, higher tumor node metastasis stage, and even shorter survival of hepatocellular carcinoma patients. Furthermore, cell and animal experiments showed that sepiapterin reductase depletion inhibited cancer cell proliferation and promoted cancer cell apoptosis. Importantly, the results suggested that sepiapterin reductase enzymatic activity was not necessary for the progression of hepatocellular carcinoma, based on the comparison between SMMC-7721 and SMMC-7721 containing sepiapterin reductase mutant. Moreover, we showed that sepiapterin reductase regulated the development of hepatocellular carcinoma via the FoxO3a/Bim-signaling pathway. Collectively, our study suggests that sepiapterin reductase controls hepatocellular carcinoma progression via FoxO3a/Bim signaling in a nonenzymatic manner, which provides a potential prognostic factor and therapeutic strategy for hepatocellular carcinoma.
