Jonathan D. Graves

Expression of matrix metalloproteinase (MMP)-9 has been linked to the progression of plaque rupture and intimal formation in arterial lesions. In this study, we determined which factors and signaling pathways are involved in regulating the MMP-9 gene. Rat carotid arterial smooth muscle cells treated with tumor necrosis factor (TNF)-alpha showed a marked increase in MMP-9 activity and mRNA level, whereas platelet-derived growth factor (PDGF) showed a slight induction of the MMP-9 mRNA level. TNF-alpha treatment caused an increase in c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (p38 MAPK), and extracellular signal-regulated kinase (ERK) activities, whereas PDGF treatment caused an increase in ERKs and p38 MAPK activities without any effect on JNK activity. Treatment with either SB203580 (inhibitor of p38 MAPK) or U0126 (inhibitor of the ERK pathway) downregulated the TNF-alpha-induced MMP-9 expression in a dose-dependent manner. Treatment of cells with TNF-alpha and PDGF together stimulated the MMP-9 expression at a level higher than that observed with either factor alone, suggesting that TNF-alpha and PDGF have a synergistic effect on MMP-9 expression in arterial smooth muscle cells. Furthermore, suboptimal inhibitory concentrations of SB203580 and U0126 together almost completely inhibited the MMP-9 expression. These results suggest that p38 MAPK and ERK pathways contribute to the transcriptional regulation of MMP-9 in arterial smooth muscle cells.

We have investigated the activation of the p38 MAPK pathway in response to CD40 engagement in multiple B cell lines and in human tonsillar B cells to define the role of p38 MAPK in proliferation, NF-kappaB activation and gene expression. Cross-linking CD40 rapidly stimulates both p38 MAPK and its downstream effector, MAPKAPK-2. Inhibition of p38 MAPK activity in vivo with the specific cell-permeable inhibitor, SB203580, under conditions that completely prevented MAPKAPK-2 activation, strongly perturbed CD40-induced tonsillar B cell proliferation while potentiating the B cell receptor (BCR)-driven proliferative response. SB203580 also significantly reduced expression of a reporter gene driven by a minimal promoter containing four NF-kappaB elements, indicating a requirement for the p38 MAPK pathway in CD40-induced NF-kappaB activation. However, CD40-mediated NF-kappaB binding was not affected by SB203580, suggesting that NF-kappaB may not be a direct target for the CD40-induced p38 MAPK pathway. In addition, SB203580 selectively reduced CD40-induced CD54/ICAM-1 expression, whereas CD40-dependent expression of CD40 and CD95/Fas and four newly defined CD40-responsive genes cIAP2, TRAF1, TRAF4/CART and DR3 were unaffected. Our observations show that the p38 MAPK pathway is required for CD40-induced proliferation and that CD40 induces gene expression via both p38 MAPK-dependent and -independent pathways.