Absence of keratin 8 confers a paradoxical microflora-dependent resistance to apoptosis in the colon

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 108; no. 4; pp. 1445 - 1450
• Main Authors: Habtezion, Aida, Toivola, Diana M, Asghar, M. Nadeem, Kronmal, Greg S, Brooks, Jacqueline D, Butcher, Eugene C, Omary, M. Bishr
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 25-01-2011; National Acad Sciences
• Subjects: Animals; Anti-Bacterial Agents - pharmacology; Antibiotics; Antibodies; Antibodies - immunology; Antibodies - pharmacology; Apoptosis; Apoptosis - drug effects; Apoptosis - genetics; Biological Sciences; Cell culture; Cell Line; Cell Proliferation - drug effects; Cells, Cultured; Colon; Colon - drug effects; Colon - metabolism; Colon - microbiology; Crypts; Drug Resistance - drug effects; Drug Resistance - genetics; Epithelial cells; Female; Focal Adhesion Kinase 1 - metabolism; Gene Expression Profiling; Genomics; Genotype & phenotype; Hepatocytes; Imipenem - pharmacology; Immunoblotting; In Situ Nick-End Labeling; Inhibitor of Apoptosis Proteins - genetics; Inhibitor of Apoptosis Proteins - metabolism; Integrin beta4 - genetics; Integrin beta4 - immunology; Integrin beta4 - metabolism; Keratin-8 - genetics; Keratin-8 - metabolism; Keratin-8 - physiology; Keratins; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Microorganisms; Mutation; Phosphorylation; Phosphorylation - drug effects; Repressor Proteins - genetics; Repressor Proteins - metabolism; Reverse Transcriptase Polymerase Chain Reaction; Rodents; Small intestine; T cell receptors; Vancomycin - pharmacology
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1010833108

Keratin 8 (K8) is a major intermediate filament protein present in enterocytes and serves an antiapoptotic function in hepatocytes. K8-null mice develop colonic hyperplasia and colitis that are reversed after antibiotic treatment. To investigate the pathways that underlie the mechanism of colonocyte hyperplasia and the normalization of the colonic phenotype in response to antibiotics, we performed genome-wide microarray analysis. Functional annotation of genes that are differentially regulated in K8⁻/⁻ and K8⁺/⁺ isolated colon crypts (colonocytes) identified apoptosis as a major altered pathway. Exposure of K8⁻/⁻ colonocytes or colon organ ("organoid") cultures, but not K8⁻/⁻ small intestine organoid cultures, to apoptotic stimuli showed, surprisingly, that they are resistant to apoptosis compared with their wild-type counterparts. This resistance is not related to inflammation per se because T-cell receptor α-null (TCR-α⁻/⁻) and wild-type colon cultures respond similarly upon induction of apoptosis. Following antibiotic treatment, K8⁻/⁻ colonocytes and organ cultures become less resistant to apoptosis and respond similarly to the wild-type colonocytes. Antibiotics also normalize most differentially up-regulated genes, including survivin and β4-integrin. Treatment of K8⁻/⁻ mice with anti-β4-integrin antibody up-regulated survivin, and induced phosphorylation of focal adhesion kinase with decreased activation of caspases. Therefore, unlike the proapoptotic effect of K8 mutation or absence in hepatocytes, lack of K8 confers resistance to colonocyte apoptosis in a microflora-dependent manner.