The epidermis comprises multiple layers of specialized epithelial cells called keratinocytes. As cells are lost from the outermost epidermal layers, they are replaced through terminal differentiation, in which keratinocytes of the basal layer cease proliferating, migrate upwards, and eventually reach the outermost cornified layers. Normal homeostasis of the epidermis requires that the balance between proliferation and differentiation be tightly regulated. The GTP binding protein RhoA plays a fundamental role in the regulation of the actin cytoskeleton and in the adhesion events that are critically important to normal tissue homeostasis. Two central mediators of the signals from RhoA are the ROCK serine/threonine kinases ROCK-I and ROCK-II. We have analyzed ROCK's role in the regulation of epidermal keratinocyte function by using a pharmacological inhibitor and expressing conditionally active or inactive forms of ROCK-II in primary human keratinocytes. We report that blocking ROCK function results in inhibition of keratinocyte terminal differentiation and an increase in cell proliferation. In contrast, activation of ROCK-II in keratinocytes results in cell cycle arrest and an increase in the expression of a number of genes associated with terminal differentiation. Thus, these results indicate that ROCK plays a critical role in regulating the balance between proliferation and differentiation in human keratinocytes.

These findings support the concept that ANCA can directly activate neutrophils to become firmly adherent to vessel walls, where they may obstruct flow, initiate tissue damage, and contribute to pathogenesis of vasculitis.

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SUMMARYNeutrophils accumulate in the acute blood vessel lesions of patients with autoimmune systemic vasculitis. They have been shown previously to produce the cytokine IL-1¯in response to stimulation with TNF. This study demonstrates that neutrophils can be stimulated by anti-neutrophil cytoplasmic antibodies (ANCA), which are present in patients with systemic vasculitis, to express mRNA and protein for IL-1¯. Both human ANCA and MoAbs to a variety of autoantigens recognized by ANCA, including proteinase 3, myeloperoxidase, bactericidal/permeability increasing protein and elastase, are effective. This response can be inhibited by actinomycin and cycloheximide, suggesting a requirement for de novo protein synthesis. IL-1¯production can be inhibited by pooled human intravenous immunoglobulins but not by FK506 or cyclosporin A. These data suggest that ANCA in patients with active vasculitis may stimulate neutrophils to produce cytokines. It is hypothesized that cytokine production from neutrophils that accumulate in significant numbers in vasculitic lesions contribute to and augment the local inflammatory response by the activation of vascular endothelial cells and infiltrating leucocytes.