Haploinsufficiency of Krüppel-like factor 4 promotes adenomatous polyposis coli-dependent intestinal tumorigenesis

The zinc finger transcription factor Krüppel-like factor 4 (KLF4) is frequently down-regulated in colorectal cancer. Previous studies showed that the expression of KLF4 was activated by the colorectal cancer tumor suppressor adenomatous polyposis coli (APC) and that KLF4 repressed the Wnt/β-catenin pathway. Here, we examined whether KLF4 plays a role in modulating intestinal tumorigenesis by comparing the tumor burdens in mice heterozygous for the Apc^Min allele (Apc^Min/+) and those heterozygous for both the Apc^Min and Klf4 alleles (Klf4^+/-/Apc^Min/+). Between 10 and 20 weeks of age, Klf4^+/-/Apc^Min/+ mice developed, on average, 59% more intestinal adenomas than Apc^Min/+ mice (P < 0.0001). Immunohistochemical staining showed that Klf4 protein levels were lower in the normal-appearing intestinal tissues of Klf4 ^+/-/Apc^Min/+ mice compared with wild-type, Klf4 ^+/-, or Apc^Min/+ mice. In contrast, the levels of β-catenin and cyclin D1 were higher in the normal-appearing intestinal tissues of Klf4^+/-/Apc^Min/+ mice compared with the other three genotypes. Klf4 levels were further decreased in adenomas from both Apc^Min/+ and Klf4^+/-/Apc^Min/+ mice compared with their corresponding normal-appearing tissues. Reverse transcription-PCR showed an inverse correlation between adenoma size and Klf4 mRNA levels in both Klf4^+/-/Apc^Min/+ and Apc^Min/+ mice. There was also a progressive loss of heterozygosity of the wild-type Apc allele in adenomas with increasing size from Klf4^+/-/Apc^Min/+ and Apc^Min/+ mice. Results from this study show that KLF4 plays an important role in promoting the development of intestinal adenomas in the presence of Apc^Min mutation.