MODULATION OF INTRACELLULAR CALCIUM LEVELS INHIBITS SECRETION OF COLLAGENASE-1 BY MIGRATING KERATINOCYTES

Calcium concentration influences keratinocyte differentiation, and, fo llowing injury, keratinocytes move through an environment of changing calcium levels. Because these migrating cells in wounds invariably exp ress collagenase 1, we assessed if modulation of calcium levels regula tes collagenase 1 production by primary human keratinocytes. Accuratel y reflecting the confined spatial pattern of enzyme production seen in vivo, collagenase 1 mRNA was expressed only by keratinocytes migratin g from foci of differentiated cells. Treatment with calcium ionophores A23187 or thapsigargin markedly inhibited the basal and phorbol 12-my ristate 13-acetate-(PMA) stimulated accumulation of keratinocyte colla genase 1 in the medium but did not affect collagenase 1 production by control or PMA-treated fibroblasts. A23187-mediated inhibition of coll agenase 1 protein was not associated with a decrease in mRNA levels bu t rather was controlled by a selective and reversible block of enzyme secretion. This block in secretion was likely not due to altered prote in folding as the proenzyme within A23187-treated cells remained capab le of autolytic activation upon treatment with p-aminophenylmercuric a cetate. In contrast, 92-kDa gelatinase mRNA and secreted protein level s were coordinately reduced by A23187. Keratin 14 expression, a basal keratinocyte marker, was reduced with PMA treatment, but A23187 did no t affect keratin 14 expression. In human wounds, both basal and suprab asal keratinocytes at the migrating front of epidermis stained for ker atin 14, but only the basal cells expressed collagenase 1. These data suggest that collagenase 1 production is not necessarily linked with e xpression of basal cell markers and that modulation of intracellular c alcium levels can block secretion of collagenase 1 by keratinocytes wh ich have moved away from the stratum basalis and from their natural su bstrate.