Inactivation of RASSF1A tumor suppressor is common in a variety of human cancers including nasopharyngeal carcinoma (NPC) and hepatocellular carcinoma (HCC). By microarray analysis, we have demonstrated that the expression of Activin beta E (INHBE), a member of TGF-β superfamily is upregulated in RASSF1A-transfected NPC cells. Although the downstream pathway of INHBE is still unknown, it is suspected that INHBE-signaling pathway is tumor suppressive based on the similarity to other known activins. In this study, we have investigated the role of INHBE in the development of HCC in which RASSF1A is frequently silenced by promoter hypermethylation. To examine the Activin beta E expression in primary tumors, immunohistochemical staining was performed on a HCC tissue micoarray containing 174 pairs of formalin-fixed, paraffin-embedded primary HCC tumor and adjacent non-malignant liver. Antibody against peptide corresponding to amino acid residues 116-126 of human activin beta E was raised in rabbit and purified by peptide-specific purification. In non-malignant hepatocyte adjacent to primary HCC, moderate to high cytoplasmic staining of Activin beta E was shown. We found that Activin beta E expression was highly reduced in 118 out of 174 primary HCCs (67.8%). Among these cases, 23 (13%) showed completed loss of Activin beta E expression when compared with corresponding non-malignant hepatocyte. The association of INHBE and RASSF1A expression in these cases has been determined. The tumor suppressor properties of INHBE and its expression in primary HCC were studied. Upregulation of INHBE expression was proven in RASSF1A-transfected HCC cell lines. Although activin family members were shown to be ligands acting through Smads, we found that both Smad 1/5/8 and Smad 2/3 were not activated by ectopically expressed INHBE. Nevertheless, significant growth inhibition was demonstrated in the transient-transfected HCC cells overexpressing INHBE. Our study suggested that INHBE is a growth inhibiting gene which mediates the tumor suppression effect of RASSF1A in HCC.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA