MITOGEN-ACTIVATED PROTEIN (MAP) KINASE IS REGULATED BY THE MAP KINASE PHOSPHATASE (MKP-1) IN VASCULAR SMOOTH-MUSCLE CELLS

Angiotensin II stimulates hypertrophic growth of vascular smooth muscle cells (VSMC) and activates many growth-promoting kinases such as mitogen activated protein (MAP) kinase, A novel transcriptionally regulated phosphatase, MAP kinase phosphatase-l (MKP-1), is induced by angiotensin II in VSMC and selectively dephosphorylates MAP kinase in vitro. Using actinomycin D and antisense oligonucleotides targeted to MKP-1, we demonstrate that MKP-1 regulates MAP kinase in VSMC. Both actinomycin D and MKP-1 antisense oligo nucleotides inhibited MKP-1 mRNA expression and caused prolonged activation of the p42 and p44 MAP kinases as measured by in-gel kinase assays and Western blot, For example, MAP kinase activity 120 min after angiotensin II treatment was 30% (range 25-35%), 79%, and 74% of maximum in control, actinomycin D-treated (3 mu g/ml, 30 min), and antisense oligonucleotide-treated (300 nM, 6 h) cells, respectively. A sense oligonucleotide was without effect (34%). MKP-1 antisense oligonucleotides did not affect the activity of MEK indicating that sustained activation of MAP kinase was due to inhibition of MKP-1 expression. These findings demonstrate that inactivation of MAP kinase by angiotensin II is mediated predominantly by MKP-1, suggesting an important role for MKP-1 and other related phosphatases in the regulation of MAP kinases in VSMC.