Selective loss of PMA-stimulated expression of matrix metalloproteinase 1 in HaCaT keratinocytes is correlated with the inability to induce mitogen-activated protein family kinases

Many cell types, including fibroblasts and primary keratinocytes, increase matrix metalloproteinase 1 (MMP-1) production in response to agonists such as growth factors and phorbol esters. However, the spontaneously transforme d human keratinocyte cell line HaCaT, although it increases MMP-1 productio n in response to epidermal growth factor (EGF), does not respond similarly to stimulation with PMA, This phenomenon occurs even though HaCaT cells rem ain proliferatively responsive to both agonists, suggesting a HaCaT-specifi c defect in a PMA-mediated signal transduction pathway. Using an inside-out approach to elucidate the source of this defect, we found that EGF, but no t PMA, stimulated MMP-1 promoter activity in transiently transfected HaCaT keratinocytes. In addition, an assessment of fibroblast and HaCaT c-fos and c-jun gene expression after exposure to EGF and PMA showed that although b oth agonists increased the expression of c-fos and c-jun mRNA in fibroblast s, only EGF did so in HaCaT keratinocytes. Finally, we looked at the activa tion of mitogen-activated protein (MAP) family kinases after stimulation wi th EGF or PMA and found that both agonists increased the phosphorylation an d activation of fibroblast extracellular signal-regulated protein kinase an d c-Jun N-terminal kinase, but only EGF activated the same kinase activitie s in HaCaT cells. Further, the EGF-mediated increase in MMP-1 gene expressi on was inhibited by the MAP kinase/ERK kinase (MEK)-specific inhibitor PD98 059 and the p38 kinase-specific inhibitor SB203580. Our evidence indicates that although HaCaT MAP kinases are functional, they are not properly regul ated in response to the activation of protein kinase C, and that the defect that bars HaCaT MMP-1 expression in response to stimulation with PMA lies before MAP kinase activation.