Down-regulation of Type 3 TGFβ receptor in Hepatocellular Carcinoma and its role in tumor promoting macrophages

Abstract

Introduction Studies show that type 3 transforming growth factor beta receptor (TGFβR3) suppresses cancer progression with different mechanisms particularly inhibiting cancer cells invasiveness and activating anti-tumor immunity. Down-regulation of TGFβR3 was commonly observed in most malignancies. Currently, the clinical imlpications and the underlying molecular mechanisms are unelucidated in Hepatocellular Carcinoma (HCC). Previously, we reported the tumor promoting capacities of M2 macrophages leading to poor survival outcome in HCC patients. Our preliminary results revealed that loss of TGFβR3 in HCC cells represent a novel mechanism in activating the tumor promoting immune population via complement product. In the present study, we aimed to study the clinical significances of TGFβR3 and its immunological impact in HCC. Materials and Methods 100 tumor specimens were obtained from HCC patients who underwent curative resection. The expression level of tissue TGFβR3 and its soluble form (sTGFβR3) in plasma were determined by q-PCR and ELISA. The tumor suppressive function of sTGFβR3 was determined in orthotopic nude mice bearing HCC tumor. Further functional and molecular studies were performed via forced TGFBR3 down-regulation in hepatocyte and up-regulation in HCC cells. Results Significant down-regulation of TGFβR3 were found in both HCC tissue and plasma (sTGFβR3) from patients compared to healthy individuals (P<0.01). We further determined that patients with <9.1ng/ml plasma sTGFβR3 developed later tumor stage, higher recurrence rate and decreased disease free survival period (P<0.05). In an orthotopic model, treatment of sTGFβR3 significantly reduced HCC tumor size by 2 fold. Interestingly, TGFβR3 knockdown hepatocyte cell line resulted the up-regulation of complement component C5a. Further clinical analysis indicated that high level of plasma C5a associated with late tumor stage and poorer disease survival, strongly correlated with sTGFβR3 (P<0.05) and tumoral M2 macrophages (P<0.05). Treatment of C5a with macrophages significantly up-regulated the pro-tumor M2 phenotypes. Conclusion Our findings indicated that TGFβR3 suppressed tumor growth and loss of the receptor in HCC contributed to poor clinical outcome. The diagnostic potential of sTGFβR3 was identified. A novel mechanistic of HCC cells in activating M2 macrophages upon the loss of TGFβR3 via C5a was revealed.