Correlation between tumor necrosis factor‐α (TNF‐α)‐induced cytoskeletal changes and human collagenase gene induction

Abstract

Tumor necrosis factor-alpha (TNF-alpha) has been shown not only to induce the biosynthesis and secretion of collagenase but also to change the organization of cytoskeletal components. In the present study we explore the correlation between the biosynthesis of collagenase (by mRNA hybridization, indirect immunofluorescence and collagenolytic activity), and cytoskeletal reorganization (by rhodamine-phalloidin staining of F-actin) induced in fibroblasts by recombinant TNF (rTNF). In the concentration range of 1-100 ng/ml, rTNF increased extracellular collagenase activity 8-fold and collagenase mRNA 4-fold. In addition, whereas the collagenase mRNA was detected as early as 24 h posttreatment, the appearance of extracellular collagenase activity required 48 h. Using phalloidin to follow the organization of the cytoskeleton we observed that rTNF disrupted the parallel array of stress fibers normally observed in the perinuclear region. In contrast to the time required to affect collagenase synthesis, the effect of rTNF on stress fiber organization occurred as early as 6 h post-treatment. Finally, while the number of cells exhibiting this change increased with increasing concentrations of rTNF, a maximum of about 30% of the cells showed this effect. Interestingly, double staining studies demonstrated that both stress fiber changes and procollagenase production occurred in the same cells. This finding, together with the observation that the cytoskeletal disorganization preceded collagenase gene induction by at least 18 h is consistent with the conclusion that the organizational status of the microfilaments may have a role as a regulator of procollagenase gene expression.