An intracellular multi-effector complex mediates somatostatin receptor 1 activation of phospho-tyrosine phosphatase eta.
The receptor-like phosphotyrosine phosphatase eta (PTPeta) is an important intracellular effector of the cytostatic action of SST. Here we characterize, in Chinese hamster ovary-k1 cells, the intracellular pathway that from somatostatin receptor 1 (SSTR1), leads to the activation of PTPeta and that involves, in a multimeric complex and sequential activation, the tyrosine kinases Janus kinase (JAK) 2 and Src, and the cytosolic phosphotyrosine phosphatase SHP-2. We show that inhibitors of JAK2 and Src and dominant-negative mutants of SHP-2 and Src abolished the SSTR1-mediated PTPeta activation, suggesting that all these effectors participate in the activation of PTPeta. In basal conditions, JAK2 forms a multimeric complex with SHP-2, Src and PTPeta. In response to SST, JAK2 is activated in a G protein-dependent manner, dissociates from and phosphorylates SHP-2, increasing its activity. Subsequently, SHP-2 dissociates from Src, dephosphorylates the Src inhibitory tyrosine-529, and causes an autocatalytical increase of the phosphorylation of Src tyrosine 418, located inside its kinase activation loop. Active Src, in turn, controls the activity of PTPeta, via a direct interaction and phosphorylation of the phosphatase. These data for the first time depict an intracellular pathway involving a precise sequence of interactions and cross-activation among tyrosine phosphatases and kinases acting upstream of PTPeta. In particular the sequential activation of JAK2, SHP-2, and Src conveys the molecular signaling from SSTR1 to the activation of this phosphatase that is responsible for the final biological effects of SST.
Arena
Sara
S
Section of Pharmacology, Department of Oncology, Biology and Genetics, Univertsity of Genova 16132 Genova, Italy.
Pattarozzi
Alessandra
A
Massa
Alessandro
A
Esteve
Jean-Pierre
JP
Iuliano
Rodolfo
R
Fusco
Alfredo
A
Susini
Christiane
C
Florio
Tullio
T
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D003600:Cytosol / Q000201:enzymology; D004789:Enzyme Activation; D005799:Genes, Dominant; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D053614:Janus Kinase 2 / Q000378:metabolism; D037342:Pertussis Toxin / Q000494:pharmacology; D011485:Protein Binding; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D017027:Protein Tyrosine Phosphatases / Q000737:chemistry* / Q000378:metabolism; D051381:Rats; D017481:Receptors, Somatostatin / Q000378:metabolism*; D015398:Signal Transduction; D019061:src-Family Kinases / Q000378:metabolism
D047908:Intracellular Signaling Peptides and Proteins; D017481:Receptors, Somatostatin; D037342:Pertussis Toxin; D053614:Janus Kinase 2; D019061:src-Family Kinases; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D017027:Protein Tyrosine Phosphatases; C516727:Ptpn11 protein, rat; C453859:phosphotyrosine phosphatase eta