A pivotal role of Kruppel-like factor 5 in regulation of cancer stem-like cells in hepatocellular carcinoma

In hepatocellular carcinoma (HCC), there exists a highly tumorigenic subset of cells defined by high expression of CD44 and CD133 that has been reported to contain cancer stem-like cells (CSCs). Kruppel-like factor 5 (KLF5) regulates many factors involved in cell cycle, migration, inflammation, angiogenesis and stemness and has cancer-promoting effects in some cancers. While some reports have indicated that KLF5 may have important roles in regulation of CSCs, what role, if any, KLF5 plays in regulation of CSCs in HCC remains to be elucidated. Flow cytometric analysis of CD44 and CD133 in HCC cell lines revealed subpopulations of CD44(High)/CD133(High) and CD44(Low)/CD133(Low) cells. We subsequently sorted these subpopulations and identified KLF5 as a gene that is significantly upregulated in CD44(High)/CD44(High) cells via RNA sequencing using next generation sequencing technology. Moreover, KLF5 overexpression enriched the CD44(High)/CD133(High) subpopulation and, consistent with the up-regulation of CD44(High)/CD133(High) cells, KLF5 overexpressing cells were more resistant to anti-cancer drugs and displayed enhanced colony-formation capacity. By contrast, knock-down of KLF5 by siRNA diminished the CD44(High)/CD133(High) subpopulation. When KLF5 was acetylated by TGF-1, the KLF5-mediated CD44(High)/CD133(High) subpopulation enrichment was abrogated. Oppositely, ectopic expression of an acetylation-deficient KLF5 mutant further increased CD44(High)/CD133(High) subpopulations as compared to cell expressing wild-type KLF5. These findings provide novel mechanistic insight into a pivotal role for KLF5 in the regulation of CSCs in HCC.