Keratin intermediate filaments convey mechanical stability and protection against stress to epithelial cells. Keratins are essential for colon health, as seen in keratin 8 knockout (K8‒/‒) mice exhibiting colitis phenotype. We hypothesized that keratins contribute to the nuclear structure and lamina in colonocytes. K8‒/‒ colonocytes in vivo exhibit significantly decreased levels of lamins A/C, B1, and B2 in a colon-specific and cell-intrinsic manner. CRISPR/Cas9- or siRNA-mediated K8 knockdown in Caco-2 cells similarly decreased lamin levels, which recovered after re-expression of K8 following siRNA treatment. Nuclear area was not decreased, and roundness was only marginally increased in cells without K8. Downregulation of K8 in adult K8flox/flox;Villin-Cre-Ert2 mice following tamoxifen administration significantly decreased lamin levels at day 4 when K8 levels had reduced to 40%. K8 loss also led to reduced levels of plectin, LINC complex, and lamin-associated proteins. While keratins were not seen in the nucleoplasm without or with leptomycin B treatment, keratins were found intimately located at the nuclear envelope and complexed with SUN2 and lamin A. Furthermore, K8 loss in Caco-2 cells compromised nuclear membrane integrity basally and after shear stress. In conclusion, colonocyte K8 couples with the nuclear lamina, and contributes to nuclear membrane integrity. [Media: see text] [Media: see text] [Media: see text]
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