Biomedical subjects

Philip Cohen

Publications and source records attributed to Philip Cohen.

At least 73 records · Page 4Linked to original sources

PubMed2002

Regulation of tyrosine hydroxylase by stress-activated protein kinases.

Recombinant human tyrosine hydroxylase (hTH1) was found to be phosphorylated by mitogen and stress-activated protein kinase 1 (MSK1) at Ser40 and by p38 regulated/activated kinase (PRAK) on Ser19. Phosphorylation by MSK1 induced an increase in Vmax and a decrease in Km for 6-(R)-5,6,7,8-tetrahydrobiopterin (BH4), while these kinetic parameters were unaffected as a result of phosphorylation by PRAK. Phosphorylation of both Ser40 and Ser19 induced a high-affinity binding of 14-3-3 proteins, but only the interaction of 14-3-3 with Ser19 increased the hTH1 activity. The 14-3-3 proteins also inhibited the rate of dephosphorylation of Ser19 and Ser40 by 82 and 36%, respectively. The phosphorylation of hTH1 on Ser19 caused a threefold increase in the rate of phosphorylation of Ser40. These studies provide new insights into the possible roles of stress-activated protein kinases in the regulation of catecholamine biosynthesis.

14-3-3 Proteins↗

PubMed2002

The serum and glucocorticoid-inducible kinase SGK1 and the Na+/H+ exchange regulating factor NHERF2 synergize to stimulate the renal outer medullary K+ channel ROMK1.

Mineralocorticoids stimulate Na(+) reabsorption and K(+) secretion in principal cells of connecting tubule and collecting duct. The involved ion channels are ENaC and ROMK1, respectively. In Xenopus oocytes, the serum and glucocorticoid-sensitive kinase SGK1 has been shown to increase ENaC activity by enhancing its abundance in the plasma membrane. With the same method, ROMK1 appeared to be insensitive to regulation by SGK1. On the other hand, ROMK1 has been shown to colocalize with NHERF2, a protein mediating targeting and trafficking of transport proteins into the cell membrane. The present study has been performed to test whether NHERF2 is required for regulation of ROMK1 by SGK1. Coexpression of neither NHERF2 nor SGK1 with ROMK1 increases ROMK1 activity. However, coexpression of NHERF2 and SGK1 together with ROMK1 markedly increases K(+) channel activity. The combined effect of SGK1 and NHERF2 does not significantly alter the I/V relation of the channel but increases the abundance of the channel in the membrane and decreases the decay of channel activity after inhibition of vesicle insertion with brefeldin. Coexpression of NHERF2 and SGK1 does not modify cytosolic pH but leads to a slight shift of pK(a) of ROMK1 to more acidic values. In conclusion, NHERF2 and SGK1 interact to enhance ROMK1 activity in large part by enhancing the abundance of channel protein within the cell membrane. This interaction allows the integration of genomic regulation and activation of SGK1 and NHERF2 in the control of ROMK1 activity and renal K(+) excretion.

Animals↗

PubMed2002

Phosphorylation of tyrosine hydroxylase in isolated mice adrenal glands.

The site-specific phosphorylation of tyrosine hydroxylase (TH) was studied in mouse adrenal tissue. On addition of arsenite, a rapid increase in Ser19 phosphorylation occurred, concomitant with phosphorylation of p38 protein kinase. This is consistent with studies in other mammals, indicating a role of stress-activated protein kinases in TH regulation.

Adrenal Glands↗

PubMed2002

MSK1 and MSK2 are required for the mitogen- and stress-induced phosphorylation of CREB and ATF1 in fibroblasts.

Using mouse knockouts for mitogen- and stress-activated protein kinase 1 (MSK1) and MSK2 and a double knockout of both MSK1 and MSK2, we show that these protein kinases are required for the stress-induced phosphorylation of transcription factors CREB and ATF1 in primary embryonic fibroblasts. In contrast mitogen-induced phosphorylation of CREB and ATF1 is greatly reduced but not totally abolished. The mitogen- and stress-induced phosphorylation of CREB at Ser133 has been linked to the transcription of several immediate early genes, including c-fos, junB, and egr1. The knockout of both MSK1 and MSK2 resulted in a 50% reduction in c-fos and junB gene transcription in response to anisomycin or UV-C radiation but only a small reduction in response to tetradecanoyl phorbol acetate or epidermal growth factor in fibroblasts. The transcription of egr1 in response to both mitogenic and stress stimuli, as well as stress-induced apoptosis, was unaffected in the MSK1/MSK2 double knockout.

Activating Transcription Factor 1↗

PubMed2001

Phosphorylation of the cytoplasmic domain of the integrin CD18 chain by protein kinase C isoforms in leukocytes.

The CD11/CD18 (beta(2)) integrins are leukocyte-specific adhesion receptors, and their ability to bind ligands on other cells can be activated by extracellular stimuli. During cell activation, the CD18 chain is known to become phosphorylated on serine and functionally important threonine residues located in the intracellular C-terminal tail. Here, we identify catalytic domain fragments of protein kinase C (PKC) delta and PKCbetaI/II as the major protein kinases in leukocyte extracts that phosphorylate a peptide corresponding to the cytoplasmic tail of the integrin CD18 chain. The sites phosphorylated in vitro were identified as Ser-745 and Thr-758. PKCalpha and PKCeta also phosphorylated these residues, and PKCalpha additionally phosphorylated Thr-760. Ser-745, a novel site, was shown to become phosphorylated in T cells in response to phorbol ester stimulation. Ser-756, a residue not phosphorylated by PKC isoforms, also became phosphorylated in T cells after phorbol ester stimulation. When leukocyte extracts were subjected to affinity chromatography on agarose to which residues 751-761 of the CD18 chain phosphorylated at Thr-758 were bound covalently, the only proteins that bound specifically were identified as isoforms of 14-3-3 proteins. Thus, PKC-mediated phosphorylation of CD18 after cell stimulation could lead to the recruitment of 14-3-3 proteins to the activated integrin, which may play a role in regulating its adhesive state or ability to signal.

Amino Acid Sequence↗

PubMed1999