Effect of pre- and postnatal ethanol exposure on protein tyrosine kinase activity and its endogenous substrates in rat cerebral cortex

The rat brain contains high levels of tyrosine-specific protein kinases (PT Ks) that specifically phosphorylate the tyrosine-containing synthetic pepti de poly(Glu(4)Tyr(1)). Using this peptide as a substrate, we have measured the protein tyrosine kinase activity in membrane and cytosolic fractions fr om the cerebral cortices of pre- and postnatal ethanol-exposed rats at time intervals of 8, 30, and 90 days. During the course of development of the c erebral cortex, PTK activity decreased both in the membrane and cytosolic f ractions from 8 and 90 days of age. Maximum activity was associated at the age of 8 days and gradually declined in the later ages (30 and 90 days) of postnatal development. However, PTK activity in the ethanol exposed rat cer ebral cortex was further decreased when compared to controls in all the age s of postnatal development in membrane as well as in cytosolic fractions. I n the presence of vanadate, a specific inhibitor of protein tyrosine phosph atases (PTPs), the PTK activity increased, indicating that the balance betw een protein tyrosine kinase and protein tyrosine phosphatase might be lost during ethanol exposure. In addition, when using an antibody specific for p hosphotyrosine, endogenous substrates for protein tyrosine kinases were ide ntified on an immunoblot of membrane and cytosolic fractions from the ethan ol-exposed rat cerebral cortex. The immunoblot showed several phosphotyrosi ne-containing proteins with molecular weights of 114, 70, 36, 34, 32, 20, a nd 14 kDa that were present in the cerebral cortex. However, higher levels of immunoreactivity of these proteins were found in the ethanol-exposed mem brane fractions when compared to control fractions-particularly at the age of 30 and 90 days. Two phosphotyrosine proteins with molecular weights of 3 8 and 40 kDa showed decreased immunoreactivity at the age of 90 days in the cytosolic fraction of an ethanol-exposed rat's cerebral cortex. The differ ences in tyrosine-specific protein kinase activity and in phosphotyrosine-c ontaining proteins observed during pre- and postnatal ethanol exposure may reflect specific functional defects in the cerebral cortex which could poss ibly underlie the mechanism contributing to fetal alcohol syndrome (FAS). ( C) 1999 Elsevier Science me. All rights reserved.