Phosphoinositide 3-Kinase Signaling Mediates β-Catenin Activation in Intestinal Epithelial Stem and Progenitor Cells in Colitis

Background & Aims

Mechanisms responsible for crypt architectural distortion in chronic ulcerative colitis (CUC) are not well understood. Data indicate that serine/threonine protein kinase Akt (Akt) signaling cooperates with Wingless (Wnt) to activate β-catenin in intestinal stem and progenitor cells through phosphorylation at Ser552 (P-β-catenin⁵⁵²). We investigated whether phosphoinositide 3-kinase (PI3K) is required for Akt-mediated activation of β-catenin during intestinal inflammation.

Methods

The class IA subunit of PI3K was conditionally deleted from intestinal epithelial cells in mice named I-pik3r1KO. Acute inflammation was induced in mice and intestines were analyzed by biochemical and histologic methods. The effects of chemically blocking PI3K in colitic interleukin-10^−/− mice were examined. Biopsy samples from patients were examined.

Results

Compared with wild-type, I-pik3r1KO mice had reduced T-cell–mediated Akt and β-catenin signaling in intestinal stem and progenitor cells and limited crypt epithelial proliferation. Biochemical analyses indicated that PI3K–Akt signaling increased nuclear total β-catenin and P-β-catenin⁵⁵² levels and reduced N-terminal β-catenin phosphorylation, which is associated with degradation. PI3K inhibition in interleukin-10^−/− mice impaired colitis-induced epithelial Akt and β-catenin activation, reduced progenitor cell expansion, and prevented dysplasia. Human samples had increased numbers of progenitor cells with P-β-catenin⁵⁵² throughout expanded crypts and increased messenger RNA expression of β-catenin target genes in CUC, colitis-associated cancer, tubular adenomas, and sporadic colorectal cancer, compared with control samples.

Conclusions

PI3K–Akt signaling cooperates with Wnt to increase β-catenin signaling during inflammation. PI3K-induced and Akt-mediated β-catenin signaling are required for progenitor cell activation during the progression from CUC to CAC; these factors might be used as biomarkers of dysplastic transformation in the colon.

Keywords: PI3K, Pik3r1, Intestinal Stem Cells, Intestinal Progenitor Cells

Abbreviations used in this paper: Akt, serine/threonine protein kinase Akt, BrdU, bromodeoxyuridine, CAC, colitis-associated cancer, CBC, crypt base columnar cell, CUC, chronic ulcerative colitis, DCAMKL, doublecortin and CaM kinase-Like, FOXO1, reduced nuclear forkhead transcriptional factor Foxo1, IEC, intestinal epithelial cells, IL, interleukin, ISC, intestinal stem cell, PCR, polymerase chain reaction, PI3K, phosphoinositide-3 kinase, P-β-catenin⁵⁵², Akt-phosphorylated β-catenin, SB, small bowel, siRNA, small interfering RNA, TA, tubular adenoma, UCD, ulcerative colitis–associated dysplasia, Wnt, Wingless, WT, wild type