title: PREX1 Protein Function Is Negatively Regulated Downstream of Receptor Tyrosine Kinase Activation by p21-activated Kinases (PAKs).
abstract: Downstream of receptor tyrosine kinase and G protein-coupled receptor (GPCR) stimulation, the phosphatidylinositol 3,4,5-trisphosphate (PIP3)-dependent Rac exchange factor (PREX) family of guanine nucleotide exchange factors (GEFs) activates Rho GTPases, leading to important roles for PREX proteins in numerous cellular processes and diseases, including cancer. PREX1 and PREX2 GEF activity is activated by the second messengers PIP3 and Gβγ, and further regulation of PREX GEF activity occurs by phosphorylation. Stimulation of receptor tyrosine kinases by neuregulin and insulin-like growth factor 1 (IGF1) leads to the phosphorylation of PREX1; however, the kinases that phosphorylate PREX1 downstream of these ligands are not known. We recently reported that the p21-activated kinases (PAKs), which are activated by GTP-bound Ras-related C3 botulinum toxin substrate 1 (Rac1), mediate the phosphorylation of PREX2 after insulin receptor activation. Here we show that certain phosphorylation events on PREX1 after insulin, neuregulin, and IGF1 treatment are PAK-dependent and lead to a reduction in PREX1 binding to PIP3 Like PREX2, PAK-mediated phosphorylation also negatively regulates PREX1 GEF activity. Furthermore, the onset of PREX1 phosphorylation was delayed compared with the phosphorylation of AKT, supporting a model of negative feedback downstream of PREX1 activation. We also found that the phosphorylation of PREX1 after isoproterenol and prostaglandin E2-mediated GPCR activation is partially PAK-dependent and likely also involves protein kinase A, which is known to reduce PREX1 function. Our data point to multiple mechanisms of PREX1 negative regulation by PAKs within receptor tyrosine kinase and GPCR-stimulated signaling pathways that have important roles in diseases such as diabetes and cancer.
authors.affiliation: From the Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, New York 10029 and the Department of Pharmacology, Columbia University, New York, New York 10032.
authors.forename: Douglas
authors.initials: D
authors.lastname: Barrows
authors.affiliation: From the Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, New York 10029 and.
authors.forename: John Z
authors.initials: JZ
authors.lastname: He
authors.affiliation: From the Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, New York 10029 and ramon.parsons@mssm.edu.
authors.forename: Ramon
authors.initials: R
authors.lastname: Parsons
mesh_terms: D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism; D015232:Dinoprostone / Q000494:pharmacology; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D061986:MCF-7 Cells; D018129:Phosphatidylinositol Phosphates / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D054462:p21-Activated Kinases / Q000235:genetics / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D020662:Guanine Nucleotide Exchange Factors; C583557:IGF1 protein, human; D007328:Insulin; C453280:PREX1 protein, human; C490712:PREX2 protein, human; D018129:Phosphatidylinositol Phosphates; C107953:RAC1 protein, human; C060974:phosphatidylinositol 3,4,5-triphosphate; D007334:Insulin-Like Growth Factor I; D011972:Receptor, Insulin; D054462:p21-Activated Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D020830:rac1 GTP-Binding Protein; D015232:Dinoprostone; D007545:Isoproterenol
keywords: G protein-coupled receptor (GPCR); Rac (Rac GTPase); guanine nucleotide exchange factor (GEF); insulin; p-21-activated kinase (PAK); phosphatidylinositol 3,4,5-trisphosphate-dependent Rac exchanger 1 (PREX1); phosphatidylinositol 3-kinase (PI 3-kinase); receptor tyrosine kinase; signal transduction