A negative feedback loop between KLF9 and the EMT program dictates metastasis of hepatocellular carcinoma

Abstract

Metastasis is the primary cause of death of hepatocellular carcinoma (HCC), while the mechanism underlying this severe disease remains largely unclear. The Kruppel‐like factor (KLF) family is one of the largest transcription factor families that control multiple physiologic and pathologic processes by governing the cellular transcriptome. To identify metastatic regulators of HCC, we conducted gene expression profiling on the MHCC97 cell series, a set of subclones of the original MHCC97 that was established by in vivo metastasis selection therefore harbouring differential metastatic capacities. We found that the expression of KLF9, a member of the KLF family, was dramatically repressed in the metastatic progeny clone of the MHCC97 cells. Functional studies revealed overexpression of KLF9 suppressed HCC migration in vitro and metastasis in vivo, while knockdown of KLF9 was sufficient to promote cell migration and metastasis accordingly. Mechanistically, we found the expression of KLF9 can reverse the pro‐metastatic epithelial‐mesenchymal transition (EMT) program via direct binding to the promoter regions of essential mesenchymal genes, thus repressing their expression. Interestingly, we further revealed that KLF9 was, in turn, directly suppressed by a mesenchymal transcription factor Slug, suggesting an intriguing negative feedback loop between KLF9 and the EMT program. Using clinical samples, we found that KLF9 was not only downregulated in HCC tissue compared to its normal counterparts but also further reduced in the HCC samples of whom had developed metastatic lesions. Together, we established a critical transcription factor that represses HCC metastasis, which is clinically and mechanically significant in HCC therapies.

Krüppel-like Factor-9 and Krüppel-like Factor-13: Highly Related, Multi-Functional, Transcriptional Repressors and Activators of Oncogenesis

“…In line with this, forced liver tumor expression of KLF9 in nude mice caused the regression of tumors accompanied by increased apoptosis and the decreased proliferation of xenografts [200]. In addition, a recent study found that over-expression of KLF9 caused suppression of metastasis of HCC tumor cells, whereas knock-down of KLF9 caused the opposite effects, ascribed, in part, to KLF9 repression of the EMT pathway [201]. KLF9 is a suppressor of oxidative stress and inflammation in the livers of high fat-fed mice [147], effects that are predicted to be tumor-preventive.…”

“…KLF9 mRNA and protein levels are significantly lower in HCC tissue than in normal non-tumor liver tissue [199][200][201]. In HepG2 human liver cancer cells, the over-expression of KLF9 (by transfection) resulted in decreased proliferation and increased apoptosis [199,200].…”