Transforming growth factor beta activates protein kinase C in microvessels isolated from immature rat brain

We investigated the activation of protein kinase C in microvessels isolated from rat brain. We found that unstimulated kinase activity in microvessels from immature animals is soluble while that from adults is particulate. The tumor promoter, phorbol 12-myristate 13-acetate, and the diacylglycerol analog, 1-oleoyl-2-acetyl-sn-glycerol, caused the redistribution of protein kinase C activity to the membrane fraction in microvessels from immature rats. Exposure to transforming growth factor beta resulted in similar redistribution of kinase activity. To our knowledge, this is the first report of an effect of transforming growth factor beta on protein kinase C. The kinase activity in microvessels from adult animals was unaffected by exposure to these agonists. We suggest that protein kinase C activation promotes differentiation of the brain microvasculature. Transforming growth factor beta may mediate this process.