Abstract
The integrin-mediated stress relaxation as it occurs in a retracting three-dimensional collagen gel (RCG) is accompanied by a large up-regulation of the interstitial collagenase, matrix metalloproteinase 1 ((MMP-1), EC 3.4.24.7), regulated notably by interleukin-1 (IL-1), phorbol esters, and cytoskeleton-disrupting drugs as cytochalasin D (CD). The repression of MMP-1 up-regulation in RCG by cycloheximide suggested the participation in the regulation process of a de novo synthesized intermediary component. We demonstrate here that culture of human skin fibroblasts in RCG or in CD- and 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated monolayers resulted in the activation of an IL-1 autocrine feedback loop that was switched off by the naturally occurring IL-1 receptor antagonist (IL-1RA), a blocker of the common IL-1 receptor. The IL-1RA did not suppress the MMP-1 up-regulation induced in RCG nor in CD-treated cells, indicating that the up-regulation of MMP-1 and the IL-1 autocrine loop occurred in an independent way, while the TPA-induced MMP-1 expression was suppressed by the receptor antagonist. The RCG- as well as the TPA-, IL-1-, and CD-induced up-regulation of both MMP-1 and IL-1 was totally suppressed by protein tyrosine kinases inhibitors. In contrast bisindoylmaleimide, at a concentration (5 microM) that inhibits the TPA-induced protein kinase C activity, suppressed the CD-induced MMP-1 expression but did not or barely altered that induced in RCG or by IL-1. None of the other tested inhibitors of a variety of signaling pathways including those used by integrins was able to suppress the RCG or CD-induced MMP-1. These results point to a potent regulation of MMP-1 by mechanical stress relaxation, a process depending on de novo protein synthesis and occurring independently of the activation of an IL-1 autocrine feedback loop.
Highlights
Integrins are transmembrane heterodimeric proteins providing a structural link between the extracellular matrix and the cytoskeleton
The Expression of MMP-1 Induced in the retracting three-dimensional collagen gel (RCG) and on Treatment of Monolayers with cytochalasin D (CD) and IL-1, but Not by TPA Requires de Novo Protein Synthesis—The expression of MMP-1 by normal human skin fibroblasts was low in monolayer on plastic (Fig. 1a) and was barely increased on a fibrous collagen-coated versus uncoated plastic (2.0 Ϯ 0.2-fold)
The maximum level of MMP-1 induction was observed after 24 h of treatment with IL-1 or TPA, but only after 48 h with CD and in RCG
Summary
Integrins are transmembrane heterodimeric proteins providing a structural link between the extracellular matrix and the cytoskeleton.
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