Methylation silencing of SOCS-3 promotes cell growth and migration by enhancing JAK/STAT and FAK signalings in human hepatocellular carcinoma

Abstract

We identified that suppressor of cytokine signaling-3 (SOCS-3) gene was aberrantly methylated in its CpG island in three of 10 human hepatocellular carcinoma (HCC) cell lines. SOCS-3 RNA was undetectable in five of the 10 HCC cell lines including the three methylated cell lines, and a demethylating agent, 5-aza-2 0 -deoxycytidine, reactivated SOCS-3 expression in three cell lines tested. The DNA region where we found aberrant DNA methylation includes a signal transducers and activators of transcription (STAT) binding consensus sequence. When the DNA region was used as a promoter, DNA methylation markedly reduced promoter activity. SOCS-3 was also aberrantly methylated in six of 18 primary HCC samples. SOCS-3 expression was reduced in three of the three methylated and one of the three unmethylated primary samples examined. Restoration of SOCS-3 in cells lacking SOCS-3 expression suppressed STAT3 phosphorylation and cell growth. We found that IL-6 acted as a growth factor in HCC cells. Inhibition of SOCS-3 expression in cells whose growth was induced by IL-6 enhanced STAT3 phosphorylation and cell growth. In addition, AG490, a chemical JAK2 inhibitor, suppressed cell growth and downregulated STAT3 phosphorylation, but not FAK phosphorylation. We also found that SOCS-3 physically interacted with phosphorylated FAK and Elongin B in HCC cells. Restoration of SOCS-3 decreased FAK phosphorylation as well as FAK protein level. Inhibition of SOCS-3 expression increased FAK phosphorylation, resulting in enhancement of cell migration. These data indicate that SOCS-3 negatively regulates cell growth and cell motility by inhibiting Janus kinase (JAK)/STAT and FAK signalings in HCC cells. Thus, loss of SOCS-3 by the associated DNA methylation confers cells advantage in growth and migration.

SOCS proteins in regulation of receptor tyrosine kinase signaling

“…Loss of SOCS2 and SOCS6 expression in hepatocellular carcinoma correlated with aggressive tumor progression and poor prognosis [85], and similar effects are seen in the case of SOCS2 and prostate cancer or breast cancer [77,86,87]. Methylation-mediated down-regulation of SOCS3 has been shown to be related to the abnormal cell growth and migration in same disease, which is mediated through loss of regulation of JAK/STAT and FAK signaling [88]. Loss of SOCS3 function results in elevated STAT5 activation leading to higher metastasis in colorectal carcinoma patients [89].…”

Signal Transducer and Activator of Transcription-3: A Molecular Hub for Signaling Pathways in Gliomas

“…SOCS-3 works in a negative-feedback loop to suppress STAT-3 signaling; therefore, it is reasonable to suggest that loss of SOCS-3 may contribute to STAT-3 activation and tumor progression. Indeed, reports describing SOCS-3 hypermethylation and subsequent loss of expression in a variety of cancers support the idea that SOCS-3 may have a tumor-suppressing function (94)(95)(96)(97). In contrast, elevated SOCS-3 expression was reported in human breast cancer and melanoma tissues, as well as in a subset of classic Hodgkin's lymphoma cell lines and primary lymphoma cells (98)(99)(100)(101)(102)(103)(104).…”

Dietary compounds as potent inhibitors of the signal transducers and activators of transcription (STAT) 3 regulatory network

“…However, NF-jB and STAT3 have been particularly implicated in cell survival, metastasis and angiogenesis of prostate tumors (Gojo et al 2002). Moreover, STAT3 is often constitutively activated in hepatocellular carcinoma (HCC) (Liu et al 2002;Niwa et al 2005) where it induces cell growth and inhibits apoptosis. Interestingly, a clear link between hepatitis C virus (HCV), STAT3 activation and HCC development has been reported (Waris and Siddiqui 2005;Yoshida et al 2002).…”