Prognostic significance of SOCS3 and its biological function in colorectal cancer

Colorectal cancer (CRC) is a common malignant tumor, in which the inflammatory microenvironment plays an important role. STAT3 signaling pathway is regarded as the "bridge" between inflammation and cancer, and involved in the development of CRC. SOCS3 is a key negative feedback regulator of JAK/STAT signaling pathway. Studies about SOCS3 gene in CRC are rarely reported. The purpose of this study is to determine the expression of SOCS3 in CRC tissue and its correlation with the clinical pathological characteristics and prognosis of colorectal cancers. The effects of SOCS3 on biological behavior such as apoptosis, proliferation, migration, invasion and tumor formation in nude mice were studied. We observed that SOCS3 expression was down regulated in CRC tissues, while IL-6, pSTAT3 were up-regulated. Inflammatory cytokines IL-6 can promote the expression of STAT3 signaling pathways while inhibit the expression of SOCS3 by promoting hypermethylation of SOCS3 gene promoters. 5-Aza-cdR treatment can reverse IL-6/STAT3 signaling pathway mediated down regulation of SOCS3 in colorectal cancer cells. Low expression of SOCS3 was correlated with lymph node metastasis and advanced clinical stage. Patients with high expression of SOCS3 in colorectal cancers often indicated a relatively good prognosis. Overexpression of SOCS3 inhibited proliferation, migration, invasion and tumorigenic ability of CRC cells while increased cell apoptosis. This study demonstrated that IL-6/STAT3 signaling activation negatively regulated SOCS3 expression, which led to imbalance and sustained activation of STAT3 signaling pathway. Reduced expression of SOCS3 promoted the growth and metastasis of colorectal cancer. Thus, targeting IL-6/STAT3/SOCS3 signaling pathway may become an important treatment strategy of colorectal cancer.