Post‐transcriptional and post‐translational regulation of PTEN by transforming growth factor‐β1

Park

Clinical Cancer Research

et al. 2011

Purpose: Gain-of-function mutations and KIT overexpression are well-known tumorigenesis mechanisms in gastrointestinal stromal tumors (GIST). This study aimed to discover microRNAs (miRNA) that target KIT and reveal the relationship between the discovered miRNAs and KIT expression in GISTs.Experimental Design: Fresh-frozen GISTs from 31 patients were used to confirm the relationship between miR-494 and KIT expression using quantitative reverse transcription-PCR to assess miR-494 expression levels and Western blotting to assess KIT protein expression levels. A luciferase assay was conducted for the target evaluation. The functional effects of miR-494 on GIST882 cells (GIST cell line with activating KIT mutation) were validated by a cell proliferation assay and fluoresce-activated cell sorting analysis.Results: An inverse relationship was found between the expression levels of miR-494 and KIT in GISTs (r ¼ À0.490, P ¼ 0.005). The direct targeting of KIT by miR-494 was shown by the reduction in KIT expression after miR-494 overexpression and the increase in KIT expression after inhibiting endogenous miR-494 expression. We showed that miR-494 regulates KIT by binding two different seed match sites. Induced miR-494 overexpression in GIST882 reduced the expression of downstream molecules in KIT signaling transduction pathways, including phospho-AKT and phospho-STAT3. Finally, miR-494 overexpression provoked apoptosis and inhibited GIST cell growth, which were accompanied by changes in G 1 and S phase content.Conclusion: Our findings indicate that miR-494 is a negative regulator of KIT in GISTs and overexpressing miR-494 in GISTs may be a promising approach to GIST treatment.

Section: Apoptosis and Cell-cycle Analysis After Mir-494 Overexpressimentioning

confidence: 99%

MicroRNA-494 Downregulates KIT and Inhibits Gastrointestinal Stromal Tumor Cell Proliferation

Park

Clinical Cancer Research

et al. 2011

“…Inflammatory cytokines also significantly alter PTEN expression as shown in non-liver cells. For example, transforming growth factor-␤ was demonstrated to decrease PTEN expression [43,[64][65][66] through post-transcriptional mechanisms possibly involving miRNA-dependent downregulation of PTEN [43,66] . In cancer cell lines, tumor necrosis factor-␣ was shown to affect PTEN expression via NFB-dependent mechanisms [33,67] .…”

Section: Pten Alterations In Nafldmentioning

confidence: 99%

PTEN in Non-Alcoholic Fatty Liver Disease/Non-Alcoholic Steatohepatitis and Cancer

Peyrou¹,

Bourgoin²,

Foti³

2010

Dig Dis

The tumor suppressor PTEN is a protein/phosphoinositide phosphatase regulating the PI3K/Akt signaling pathway and is mutated or deleted in a variety of human cancers, including hepatocellular carcinoma (HCC). Accumulating evidence indicates that alterations of PTEN expression and activity in hepatocytes are common and recurrent molecular events associated with liver disorders of various etiologies including obesity, the metabolic syndrome, hepatitis B virus/hepatitis C virus infection and abusive alcohol consumption. Genetic and molecular studies, particularly in the context of non-alcoholic fatty liver disease (NAFLD), support a critical role for PTEN in hepatic insulin sensitivity and the development of steatosis, steatohepatitis and fibrosis. PTEN mutations/deletion or low PTEN expression are also associated with diverse liver malignancies, suggesting a critical role for PTEN in hepatic cancers. This review provides an overview of the current knowledge on pathological dysregulations of PTEN expression/activity in the liver with obesity and the metabolic syndrome, and the role of this enzyme in the development of non-alcoholic fatty liver disease and hepatocellular carcinoma.

“…increasing evidence suggests that this pathway is abnormally regulated in Hcc and plays a central role in tumorigenesis and the maintenance of tumor growth (30)(31)(32). in addition, targeted inhibition of this pathway has been regarded as an alternative approach for the treatment of Hcc (33,34).…”

Section: Discussionmentioning

confidence: 99%

Lentiviral-mediated Smad4 RNAi promotes SMMC-7721 cell migration by regulation of MMP-2, VEGF and MAPK signaling

Ji¹

2010

Mol Med Rep

Abstract. Hepatocellular carcinoma (Hcc) is a highly malignant cancer characterized by rapid progression, easy metastasis and frequent recurrence. Previous studies have shown that the Smad4 signaling pathway plays an important role in the cell growth and apoptosis of Hcc. However, the effect of Smad4 signaling on the invasion and migration of Hcc cells remains unclear. The present study aimed to examine the effects of the transforming growth factor (TGF)-β1-Smad4 signaling pathway on the migration of Hcc cells. lentiviral vectors expressing mirna against Smad4 were constructed to block the expression of Smad4 in Hcc cells, and transwell units were used to investigate the invasive potential of SMMc-7721 cells before and after TGF-β1 treatment. mrna levels of matrix metalloproteinase (MMP)-2 and -9 were analyzed by reverse-transcription Pcr, and concentrations of vascular endothelial growth factor (VeGF), p-JnK, p-p38 and p-erk1/2 proteins were analyzed by Western blotting. The results indicate that TGF-β1 induced cellular invasion in the SMMc-7721 cells. These effects were almost completely blocked by the knockdown of Smad4. reverse-transcription Pcr and Western blot analysis revealed that MMP-2, VeGF, p-JnK and p-p38 were up-regulated by the silencing of Smad4, while the expression of MMP-9 and p-erk1/2 was not affected by Smad4 silencing with or without TGF-β1 stimulation. These findings suggest that TGF-β1-induced SMMc-7721 cell invasion by the up-regulation of MMP-2 and VeGF is Smad4-dependent. The activation of MMP-2 and VeGF may be an important mechanism by which Smad4 is involved in metastasis. TGF-β1-Smad4 signaling may regulate SMMc-7721 cell migration through the activation of the MaPK pathway.