Krüppel-like factor 9 (KLF9) prevents colorectal cancer through inhibition of interferon-related signaling

Abstract

Expression of the transcription factor Krüppel-like factor 9 (KLF9) is frequently reduced in colorectal cancers, although a tumor suppressive role has not been established. To determine if KLF9 suppresses intestinal adenoma formation, we generated mice of distinct Klf9 genotypes in the background of the ApcMin/+ mouse and compared their adenoma burdens at 16 weeks of age. While small intestine adenoma burden remained unchanged among Klf9 genotypes, male and female ApcMin/+/Klf9-/- and ApcMin/+/Klf9+/- mice exhibited significantly more colon adenomas than their ApcMin/+/Klf9+/+ counterparts. Microarray analysis showed significant increases in the expression of interferon-induced genes in the colon mucosa of female ApcMin/+/Klf9+/- and ApcMin/+/Klf9-/- compared to ApcMin/+/Klf9+/+mice, prior to overt adenoma occurrence. Gene upregulation was confirmed by qPCR of colon mucosa and by siRNA knockdown of KLF9 in human HT29 colorectal cancer cells. Increases in expression of these genes were further augmented by supplementation with Interferon ß1. Circulating levels of the cytokine, interferon-stimulated gene 15 (ISG15) were increased in ApcMin/+/Klf9+/- and ApcMin/+/Klf9-/- mice relative to ApcMin/+/Klf9+/+. Additionally, colon mucosal levels of ISG15 were increased in ApcMin/+/Klf9+/- mice. Chromatin immunoprecipitation demonstrated KLF9 recruitment to the ISG15 promoter. Lastly, treatment with ISG15 suppressed apoptosis in HT29 cells, in the presence and absence of 5-fluorouracil (5FU). Results show KLF9 to be a haploinsufficient suppressor of colon tumorigenesis in ApcMin/+ mice in part, by repression of ISG15 and the latter's antiapoptotic function.