title: Absence of keratin 8 confers a paradoxical microflora-dependent resistance to apoptosis in the colon.
abstract: 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.
authors.affiliation: Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48109, USA. aidah@stanford.edu
authors.forename: Aida
authors.initials: A
authors.lastname: Habtezion
authors.forename: Diana M
authors.initials: DM
authors.lastname: Toivola
authors.forename: M Nadeem
authors.initials: MN
authors.lastname: Asghar
authors.forename: Greg S
authors.initials: GS
authors.lastname: Kronmal
authors.forename: Jacqueline D
authors.initials: JD
authors.lastname: Brooks
authors.forename: Eugene C
authors.initials: EC
authors.lastname: Butcher
authors.forename: M Bishr
authors.initials: MB
authors.lastname: Omary
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D000906:Antibodies / Q000276:immunology / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D003106:Colon / Q000187:drug effects* / Q000378:metabolism / Q000382:microbiology; D004351:Drug Resistance / Q000187:drug effects / Q000235:genetics; D005260:Female; D051417:Focal Adhesion Kinase 1 / Q000378:metabolism; D020869:Gene Expression Profiling; D015378:Imipenem / Q000494:pharmacology; D015151:Immunoblotting; D020287:In Situ Nick-End Labeling; D051034:Inhibitor of Apoptosis Proteins / Q000235:genetics / Q000378:metabolism; D039663:Integrin beta4 / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D053533:Keratin-8 / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010766:Phosphorylation / Q000187:drug effects; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000077022:Survivin; D014640:Vancomycin / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D000906:Antibodies; C117749:Birc5 protein, mouse; D051034:Inhibitor of Apoptosis Proteins; D039663:Integrin beta4; D053533:Keratin-8; D012097:Repressor Proteins; D000077022:Survivin; D014640:Vancomycin; D015378:Imipenem; D051417:Focal Adhesion Kinase 1; C496051:Ptk2 protein, mouse