Joan M. Boylan

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The phosphorylation of ribosomal protein S6 is thought to be required for biosynthesis of the cell's translational apparatus, a critical component of cell growth and proliferation. We have studied the signal transduction pathways involved in hepatic S6 phosphorylation during late gestation in the rat. This is a period during which hepatocytes show a high(More)
Fetal growth retardation, a common end point for a variety of conditions affecting mother and fetus, is associated with reduced liver mass. We have performed studies to determine the mechanism for decreased liver mass in a maternal starvation model of fetal growth restriction in the rat. Pregnant dams were deprived of food for 48 h before delivery on(More)
We previously isolated and characterized a coding region determinant-binding protein (CRD-BP) that might regulate c-myc mRNA post-transcriptionally. CRD-BP binds specifically to the coding region of c-myc mRNA and might stabilize c-myc mRNA in vitro by protecting it from endonucleolytic cleavage. Since c-myc abundance is regulated during embryonic(More)
We have studied the role of mitogen-activated protein (MAP) kinases in fetal hepatocyte growth in vitro and in vivo. With myelin basic protein (MBP) as the phosphate acceptor, kinase activity in cultured fetal hepatocyte lysates increased fourfold after exposure to transforming growth factor-alpha (TGF-alpha) for 10 min. This TGF-alpha-responsive MBP kinase(More)
BACKGROUND Our understanding of signal transduction networks in the physiological context of an organism remains limited, partly due to the technical challenge of identifying serine/threonine phosphorylated peptides from complex tissue samples. In the present study, we focused on signaling through the mammalian target of rapamycin (mTOR) complex 1 (mTORC1),(More)
The involvement of tyrosine phosphorylation in insulin action led us to hypothesize that increased activity of protein tyrosine phosphatases (PTPases) might contribute to insulin resistance in alloxan diabetes in the rat. Hepatic PTPase activity was measured using two artificial substrates phosphorylated on tyrosine: reduced, carboxyamidomethylated, and(More)
Polypeptide hormone signal transmission by receptor tyrosine kinases requires the rapid reversal of tyrosine phosphorylation by protein phosphotyrosine phosphatases (PPTPases). We studied hepatic PPTPases in the rat with emphasis on acute and chronic regulation by insulin. PPTPase activity with artificial substrates ([32P]Tyr-reduced,(More)
Perturbations of fetal growth produce parallel but disproportionate changes in fetal liver growth that correlate with circulating fetal insulin concentration. We have studied the effects of insulin and two hepatotrophic factors, transforming growth factor-alpha (TGF alpha) and hepatocyte growth factor (HGF), on DNA synthesis by fetal and adult rat(More)
We have studied the role of protein tyrosine phosphatases (PTPases) during neuronal differentiation of PC12 cells. Nerve growth factor (NGF), a well-characterized differentiating agent for these cells, led to a decrease in DNA synthesis within 24 h. This was accompanied by a 2- to 3-fold increase in the activity of PTPases, measured as the dephosphorylation(More)