| KLF6 is a ubiquitously expressed Krüppel-like transcription factor frequently mutated in cancer that has roles in cellular proliferation, apoptosis, differentiation, and development. Inactivation of KLF6 is an early event in hepatocellular carcinoma (HCC), commonly associated with hepatitis C virus (HCV) infection, and reduced tumor expression of KLF6 is associated with decreased survival. In light of this, the purpose of this work is to better understand the mechanisms of KLF6 involvement in the pathogenesis of hepatocellular carcinoma (HCC), in terms of downstream target genes and upstream protein regulators.;The following work highlights KLF6 target genes that are altered in hepatocellular carcinoma (HCC) and novel mechanisms of KLF6 regulation by phosphorylation and protein-protein interactions. First, we show that KLF6 heterozygosity in mice results in de-repression of the PTTG1 oncogene and loss of the tumor suppressor, GADD45γ. We have found both PTTG1 and GADD45γ to be novel KLF6 target genes, whose dysregulation may pre-disposes to the development of HCC. To further understand how KLF6 can differentially regulate such a wide range of transcriptional targets, we used a commercial yeast two-hybrid screen with a liver prey library to identify a hypothetical KLF6-interacting protein Tti1 (KIAA0406). Studies of KLF6 post-translational regulation have explored the basis for loss of function of KLF6 mutations cloned from human HCC, which disrupt the target consensus site for Glycogen Synthase Kinase 3 β (GSK3β). We have confirmed that KLF6 directly interacts with, and is phosphorylated by GSK3β, which leads to increased KLF6 protein abundance, transactivation of p21, and augmented KLF6 mediated growth suppression. Together these studies uncover important upstream regulators of KLF6 structure and function, and downstream targets of this tumor suppressor. These findings expand our understanding of KLF6 and its contribution to HCC. |
