Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P61278 (somatostatin)
 22,083 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ligand-activated somatostatin receptors (SSTRs) initiate cytotoxic or cytostatic antiproliferative signals. We have previously shown that cytotoxicity leading to apoptosis was signaled solely via human (h) SSTR subtype 3, whereas the other four hSSTR subtypes initiated a cytostatic response that led to growth inhibition. In the present study we characterized the antiproliferative signaling mediated by hSSTR subtypes 1, 2, 4, and 5 in CHO-K1 cells. We report here that cytostatic signaling via these subtypes results in induction of the retinoblastoma protein Rb and G1 cell cycle arrest. Immunoblot analysis revealed an increase in hypophosphorylated form of Rb in agonist-treated cells. The relative efficacy of these receptors to initiate cytostatic signaling was hSSTR5 > hSSTR2 > hSSTR4 approximately = hSSTR1. Cytostatic signaling via hSSTR5 also induced a marginal increase in cyclin-dependent kinase inhibitor p21. hSSTR5-initiated cytostatic signaling was G protein dependent and protein tyrosine phosphatase (PTP) mediated. Octreotide treatment induced a translocation of cytosolic PTP to the membrane, whereas it did not stimulate PTP activity when added directly to the cell membranes. C-tail truncation mutants of hSSTR5 displayed progressive loss of antiproliferative signaling proportional to the length of deletion, as reflected by the marked decrease in the effects of octreotide on membrane translocation of cytosolic PTP, and induction of Rb and G1 arrest. These data demonstrate that the C-terminal domain of hSSTR5 is required for cytostatic signaling that is PTP dependent and leads to induction of hypophosphorylated Rb and G1 arrest.
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PMID:C-terminal region of human somatostatin receptor 5 is required for induction of Rb and G1 cell cycle arrest. 989 14

The mitogen activated protein (MAP) kinase cascade represents one of the major regulator of cell growth by hormones and growth factors. However, although the activation of this intracellular pathway has been often regarded as mediator of cell proliferation, in many cell types the increase in MAP kinase (also called extra-cellular signal regulated kinase: ERK) activity may result in cell growth arrest, depending on the length or the intensity of the stimulation. In this review we examine recent data concerning the effects of somatostatin on the MAP kinase cascade through one of its major receptor subtype, the somatostatin receptor 1 (SSTR1), stably expressed in CHO-K1 cells. Somatostatin inhibits the proliferative effects of basic FGF (bFGF) in CHO-SSTR1 cell line. However, in these cells, somatostatin robustly activates the MAP kinase and augments bFGF-induced stimulation of ERK. We show that the activation of ERK via SSTR1 is mediated by the betagamma subunit of a pertussis toxin-sensitive G-protein and requires both the small G protein Ras and the serine/threonine kinase Raf-1. Moreover the phosphatidyl inositol-3kinase and the cytosolic tyrosine kinase c-src participate in the signal transduction regulated by SSTRI to activate ERK, as well as it is involved the protein tyrosine phosphatase (PTP) SHP-2. Previous studies have suggested that somatostatin-stimulated PTP activity mediates the growth inhibitory actions of somatostatin, in CHO-SSTR1 cells. Thus, the activation of SHP-2 by SSTR1 may mediate the antiproliferative activity of somatostatin. SHP-2 may. in turn, regulate the activity of kinases upstream of ERK that require tyrosine dephosphorylation to be activated, such as c-src. Finally, the synergism between somatostatin and bFGF in the activation of ERK results in an increased expression of the cyclin-dependent kinase inhibitor p21cip/WAF1 as molecular effector of the antiproliferative activity of somatostatin.
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PMID:Somatostatin receptor 1 (SSTR1)-mediated inhibition of cell proliferation correlates with the activation of the MAP kinase cascade: role of the phosphotyrosine phosphatase SHP-2. 1108 1

The G protein-coupled sst2 somatostatin receptor is a critical negative regulator of cell proliferation. sstII prevents growth factor-induced cell proliferation through activation of the tyrosine phosphatase SHP-1 leading to induction of the cyclin-dependent kinase inhibitor p27Kip1. Here, we investigate the signaling molecules linking sst2 to p27Kip1. In Chinese hamster ovary-DG-44 cells stably expressing sst2 (CHO/sst2), the somatostatin analogue RC-160 transiently stimulates ERK2 activity and potentiates insulin-stimulated ERK2 activity. RC-160 also stimulates ERK2 activity in pancreatic acini isolated from normal mice, which endogenously express sst2, but has no effect in pancreatic acini derived from sst2 knock-out mice. RC-160-induced p27Kip1 up-regulation and inhibition of insulin-dependent cell proliferation are both prevented by pretreatment of CHO/sst2 cells with the MEK1/2 inhibitor PD98059. In addition, using dominant negative mutants, we show that sst2-mediated ERK2 stimulation is dependent on the pertussis toxin-sensitive Gi/o protein, the tyrosine kinase Src, both small G proteins Ras and Rap1, and the MEK kinase B-Raf but is independent of Raf-1. Phosphatidylinositol 3-kinase (PI3K) and both tyrosine phosphatases, SHP-1 and SHP-2, are required upstream of Ras and Rap1. Taken together, our results identify a novel mechanism whereby a Gi/o protein-coupled receptor inhibits cell proliferation by stimulating ERK signaling via a SHP-1-SHP-2-PI3K/Ras-Rap1/B-Raf/MEK pathway.
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PMID:sst2 Somatostatin receptor inhibits cell proliferation through Ras-, Rap1-, and B-Raf-dependent ERK2 activation. 1287 7

(1) Here, we introduce a beta-casomorphin-5-derived cyclic pentapeptide, cCD-2 (Tyr-cyclo[d-Orn-Tyr(Bzl)-Pro-Gly]), which inhibits the cell growth of a variety of human cancer cell lines. (2) This opioid-derived peptide possesses only low affinity for mu-receptors, but enhances the agonist binding to mu-receptors in vitro and potentiates the analgesic effect of morphin in vivo. The molecular mechanism of mu-receptor sensitization by cCD-2 is not yet known. (3) The antiproliferative effect of cCD-2 is independent of mu-, delta-, and kappa-receptors. (4) Using SH-SY5Y cells as model, we can demonstrate that cCD-2 specifically binds to somatostatin receptors and stimulates the activity of protein tyrosine phosphatases, which are early downstream targets of SST receptors. (5) In SH-SY5Y cells, cCD-2 specifically increases the activity of the cytosolic PTP SHP-2, stimulates the activity of mitogen-activated protein kinase (MAPK), and elevates the expression of the cyclin-dependent kinase inhibitor p21 (WAF1/Cip1), suggesting the involvement of SSTR1 receptor subtype in cCD-2 action in this cell type. (6) In COS-7 cells, for comparison, we found a stimulation of SHP-2 as well as SHP-1 in response to cCD-2. The activation of SHP-1, which is attributed to the SSTR2 receptor and negatively regulates the EGF receptor, corresponds with the ability of cCD-2 to inhibit the EGF-induced MAPK activation in COS-7 cells. (7) Our results show that in SH-SY5Y cells cCD-2 inhibits cell growth via the SSTR1 receptor-signalling pathway but may, in other cells, also use other SSTR subtypes and their signalling mechanisms. (8) cCD-2 represents a novel type of opioid-derived antiproliferative SST receptor agonist, which possesses low mu-receptor affinity but may induce mu-receptor sensitization and is structurally different from the hitherto known SST receptor agonists.
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PMID:Tyr-c[D-Orn-Tyr(Bzl)-Pro-Gly]: a novel antiproliferative acting somatostatin receptor agonist with mu-opioid receptor-sensitizing properties. 1296 30