Expression of PTEN,PPM1A and P-Smad2 in hepatocellular carcinomas and adjacent liver tissues

AIM: To investigate the expressions of PTEN, PPM1A and P-Smad2 in hepatocellular carcinoma (HCC) and their significance. METHODS: The expressions of PTEN, PPM1A and P-Smad2 in 31 HCC tissues, 25 adjacent liver tissues and 13 non-tumor liver tissues were detected by using Envision immunohistochemical technique. RESULTS: The positive expression (64.52%) and staining intensity (4.19 ± 3.31) of PTEN in the cytoplasm of HCC were significantly lower and weaker than those in the adjacent or non-tumor liver tissues (97.37%, 7.88 ± 0.93; 100%, 7.77 ± 0.93, respectively) (P < 0.05), and its staining intensity in the cytoplasm of HCC, which belongs to Edmondson pathologic grades Ⅱ-Ⅲ and above, was also lower than that of gradeⅠandⅠ-Ⅱ. Furthermore, its location in the nucleus or cytoplasm of liver cells was negatively correlated with the progression of liver disease (r = -0.339, P = 0.002); most of PPM1A might be only expressed in the nucleus of adjacent liver tissues, non-HCC tissues or Edmondson gradeⅠandⅠ-Ⅱ HCC, but it was mainly expressed in the cytoplasm of HCC with Edmondson grade ≥Ⅱ, weakly or negatively expressed in the nucleus (P < 0.05), and its location was negatively correlated with the progression of liver disease (r = -0.45, P = 0.0000). P-Smad2, which was mostly located in the nucleus and cytoplasm of gradeⅠ andⅠ-Ⅱ HCC, surrounding or non-tumor liver tissues, was only in the nucleus of HCC with Edmondson grade Ⅱ and above (P < 0.001), and its location was positively correlated with the disease progression (r = 0.224, P = 0.016). Spearman correlation analysis revealed that P-Smad2 was significantly negatively correlated with PTEN and PPM1A (r = -0.748, P = 0.000; r = -0.366, P = 0.001, respectively); and PTEN and PPM1A were positively correlated with HCC carcinogenesis (r = 0.428, P = 0.000). CONCLUSION: The aberrant location of expression and staining intensity of PTEN, PPM1A and P-Smad2 in HCC and their relationship might have an impact on the pathogenesis of HCC.

Imatinib blocks tyrosine phosphorylation of Smad4 and restores TGF-β growth-suppressive signaling in BCR-ABL1-positive leukemia

Loss of TGF-β-mediated growth suppression is a major contributor to the development of cancers,best exemplified by loss-offunction mutations in genes encoding components of the TGF-βsignaling pathway in colorectal and pancreatic cancers.Alternatively,gain-of-function oncogene mutations can also disrupt antiproliferative TGF-βsignaling.However,the molecular mechanisms underlying oncogene-induced modulation of TGF-βsignaling have not been extensively investigated.Here,we show that the oncogenic BCR-ABL1 of chronic myelogenous leukemia(CML)and the cellular ABL1 tyrosine kinases phosphorylate and inactivate Smad4 to block antiproliferative TGF-βsignaling.Mechanistically,phosphorylation of Smad4 at Tyr195,Tyr301,and Tyr322 in the linker region interferes with its binding to the transcription co-activator p300/CBP,thereby blocking the ability of Smad4 to activate the expression of cyclin-dependent kinase(CDK)inhibitors and induce cell cycle arrest.In contrast,the inhibition of BCR-ABL1 kinase with Imatinib prevented Smad4 tyrosine phosphorylation and re-sensitized CML cells to TGF-β-induced antiproliferative and pro-apoptotic responses.Furthermore,expression of phosphorylation-site-mutated Y195F/Y301F/Y322F mutant of Smad4 in Smad4-null CML cells enhanced antiproliferative responses to TGF-β,whereas the phosphorylation-mimicking Y195E/Y301E/Y322E mutant interfered with TGF-βsignaling and enhanced the in vivo growth of CML cells.These findings demonstrate the direct role of BCR-ABL1 tyrosine kinase in suppressing TGF-βsignaling in CML and explain how Imatinib-targeted therapy restored beneficial TGF-βanti-growth responses.

WDR74 functions as a novel coactivator in TGF-β signaling

Smads are critical intracellular signal transducers for transforming growth factor-β(TGF-β) in mammalian cells. In this study, we have identified WD repeat-containing protein 74(WDR74) as a novel transcriptional coactivator for Smads in the canonical TGF-β signaling pathway. Through direct interactions with Smad proteins, WDR74 enhances TGF-β-mediated phosphorylation and nuclear accumulation of Smad2 and Smad3. Consequently, WDR74 enables stronger transcriptional responses and more robust TGF-β-induced physiological responses. Our findings have elucidated a critical role of WDR74 in regulating TGF-β signaling.