ROLE OF TGF-β1 AND <i>C-Kit </i>MUTATIONS IN HEPATOCELLULAR CARCINOMA PROGRESSION IN PATIENTS WITH HEPATITIS C VIRUS: <i>in vitro </i>STUDY
Transforming growth factor-β (TGF-β) is a tumor-suppressing cytokine in normal and non-malignant conditions. Yet, in malignancy, TGF-β can exert opposite effects that cancer cells may exploit for their benefits. C-Kit plays a prominent role in stem cell activation and liver regeneration after injury. However, little is known about cross-talk between TGF-β and C-Kit and its role in hepatocellular carcinoma (HCC) progression. Here, we studied the effect of increasing doses of TGF-β1 on CD44<sup>+</sup>CD90<sup>+</sup> liver stem cells (LSCs) and <i>C-Kit</i> gene expression using malignant and adjacent non-malignant liver tissues excised from 32 HCC patients. Results showed that malignant LSCs percentage was 2.0-fold higher compared to their non-malignant counterparts. When treated with increasing doses of TGF-β1, malignant and non-malignant LSCs were progressively suppressed, but low TGF-β1 dose failed to suppress malignant LSCs. Moreover, <i>C-Kit</i> exons 9 and 11 were not expressed in non-malignant LSCs, in contrast to their malignant counterparts. Mutation analysis of <i>C-Kit</i> detected mutations in exon 9, but not in exon 11, in some malignant liver cells resulting in changes of amino acid sequence and in the deregulated protein structure and function. Interestingly, in malignant liver cells, mutated exon 9 was shown to be associated with high-level hepatitis C virus (HCV) viremia, and its expression was not suppressed by TGF-β1 treatment at all doses. To our knowledge, this is the first report that the <i>C-Kit</i> gene is mutated in patients with HCC associated with high-level HCV viremia. Our study underscores the need to investigate TGF-β1 level and <i>C-Kit</i> mutations in patients with chronic HCV for HCC prevention and better therapeutic management.