Functional study of apoptosis inducing protein in human cholangiocarcinoma

Apoptosis-inducing protein (AIP) is a secreted protein, synthesized by adipocytes and epithelial cells, that is downregulated in breast, colorectal, gastric, liver, and lung cancers, portending a poor prognosis. AIP is a potential biomarker of cancer progression, but its role in cholangiocarcinoma, a cancer of the bile duct, remains unknown. In this study, we found that AIP mRNA, but not protein, is expressed in cholangiocarcinoma. However, AIP protein overexpression induced cell death, apoptosis, and sub-G1 arrest. Importantly, AIP-induced apoptotic changes were blocked by knockdown of the pro-apoptotic protein BID, suggesting that AIP-induced apoptosis occurs via BID-dependent pathways. Mechanistically, ELF25 (E74 Like ETS Transcription Factor 1) directly targets AIP by ubiquitination and degradation. Similarly, AIP protein expression was downregulated in cholangiocarcinoma, thus negatively correlating with ELF25 expression in this cancer. Of note, low AIP, combined with high ELF25, expression, correlated with short patient survival in cholangiocarcinoma. Additionally, ELF25 knockdown led to AIP upregulation, to inhibit growth of cancer cells. Taken together, these results suggest that AIP could be a potential therapeutic target or a diagnostic biomarker, to treat patients with this insidious malignancy. Keywords: apoptosis-inducing protein, apoptosis, therapeutic target, biomarker, cholangiocarcinoma.Maste

Mutation SVCT2 promotes cell proliferation, invasion and migration in colorectal cancer

The sodium-dependent vitamin C transporter 2 (SVCT2) surface glycoprotein regulates ascorbate accumulation in the plasma, often resulting in the induction of cancer cell death. Therefore, high expression of this gene associates with increased overall survival in several cancers. However, in colorectal cancer (CRC), high (likely mutated) SVCT2 expression relates to poor overall survival, and its functional significance has not been studied. Thus, we hypothesize that mutant SVCT2 expression could affect CRC patient survival. According to biological databases, SVCT2 has been found to be mutated frequently, and SVCT2 E264K has a particularly high pathogenic score (0.98), compared to other SVCT2 mutant sites, in CRC patients. Interestingly, our results reveal expression of SVCT2 E264K in many CRC tissues and cells. Also, we found wild-type SVCT2 expression to be largely localized to the cytoplasm and membrane, while SVCT2 E264K was restricted to the cytoplasm. We further found that SVCT2 E264K overexpression increases cell growth. By contrast, SVCT2 E264K knockdown significantly reduced cell proliferation and promoted cell apoptosis, resulting in inhibition of cell invasion and migration. Taken together, SVCT2 E264K plays a critical role in proliferation in CRC. Our results suggest that SVCT2 E264K could be a promising novel therapeutic target in CRC

Role of p53 in transcriptional repression of SVCT2

SVCT2, Sodium-dependent Vitamin C Transporter 2, uniquely transports ascorbic acid (also known as vitamin C and ascorbate) into all types of cells. Vitamin C is an essential nutrient that must be obtained through the diet and plasma levels are tightly regulated by transporter activity. Vitamin C plays an important role in antioxidant defenses and is a cofactor for many enzymes that enable hormone synthesis, oxygen sensing, collagen synthesis and epigenetic pathways. Although SVCT2 has various functions, regulation of its expression/activity remains poorly understood. We found a p53-binding site, within the SVCT2 promoter, using a transcription factor binding-site prediction tool. In this study, we show that p53 can directly repress SVCT2 transcription by binding a proximal- (similar to-185 to -171 bp) and a distal- (similar to-1800 to -1787 bp) p53-responsive element (PRE), Chromatin immunoprecipitation assays showed that PRE-bound p53 interacts with the corepressor-histone deacetylase 3 (HDAC3), resulting in deacetylation of histones Ac-H4, at the proximal promoter, resulting in transcriptional silencing of SVCT2. Overall, our data suggests that p53 is a potent transcriptional repressor of SVCT2, a critical transporter of diet-derived ascorbic acid, across the plasma membranes of numerous essential tissue cell types