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Accueil > Agenda > Les séminaires Jean Roche > Récepteur somatostatinergique SST2 dans la prolifération cellulaire (...)

Récepteur somatostatinergique SST2 dans la prolifération (...)

Lundi 6 juin 2005, 11h, salle Lissitzky.


1 : Ann N Y Acad Sci. 2004 Apr ;1014:121-31.

Molecular signaling of somatostatin receptors.

Lahlou H, Guillermet J, Hortala M, Vernejoul F, Pyronnet S, Bousquet C, Susini C.

INSERM U 531, IFR 31, CHU Rangueil, 31403 Toulouse Cedex 4, France.

Somatostatin is a neuropeptide family that is produced by neuroendocrine, inflammatory, and immune cells in response to different stimuli. Somatostatin acts as an endogenous inhibitory regulator of various cellular functions including secretions, motility, and proliferation. Its action is mediated by a family of G-protein-coupled receptors (called sst1-sst5) that are widely distributed in the brain and periphery. The five receptors bind the natural peptides with high affinity, but only sst2, sst5, and sst3 bind the short synthetic analogs used to treat acromegaly and neuroendocrine tumors. This review covers the current knowledge in somatostatin receptor biology and signaling.

2 : Dig Liver Dis. 2004 Feb ;36 Suppl 1:S2-7.

Somatostatin receptors and regulation of cell proliferation.

Bousquet C, Guillermet J, Vernejoul F, Lahlou H, Buscail L, Susini C.

INSERM U531, IFR 31, CHU Rangueil, 31403 Toulouse Cedex 4, France.

Somatostatin is an inhibitory neuropeptide, which acts on various targets throughout the body to regulate a variety of physiological functions including inhibition of endocrine and exocrine secretions, modulation of neurotransmission, motor and cognitive functions, inhibition of intestinal motility, absorption of nutrients and ions, vascular contractility and inhibition of normal and tumour cell proliferation. It exerts its effects through interaction with five somatostatin receptors (sst1-sst5), which belong to the family of G-protein-coupled receptors with seven transmembrane spanning domains and are variably expressed in a variety of tumours such as gastroenteropancreatic tumours, pituitary tumours, and carcinoid tumours. This review covers the present knowledge regarding the molecular mechanisms involved in somatostatin antineoplastic activity. Evidence that sst2 receptor acts as a tumour suppressor is also discussed.

3 : J Biol Chem. 2003 Oct 10 ;278(41):39356-71. Epub 2003 Jul 22.

sst2 Somatostatin receptor inhibits cell proliferation through Ras-, Rap1-, and B-Raf-dependent ERK2 activation.

Lahlou H, Saint-Laurent N, Esteve JP, Eychene A, Pradayrol L, Pyronnet S, Susini C.

INSERM U531, IFR31, Centre Hospitalier Universitaire Rangueil, 1 avenue Jean Poulhes, 31403 Toulouse Cedex and CNRS Unite Mixte de Recherche 146, Institut Curie, Centre Universitaire, 91405 Orsay Cedex, France.

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.

4 : Mol Biol Cell. 2003 Sep ;14(9):3911-28. Epub 2003 Jul 11.

Critical role of Src and SHP-2 in sst2 somatostatin receptor-mediated activation of SHP-1 and inhibition of cell proliferation.

Ferjoux G, Lopez F, Esteve JP, Ferrand A, Vivier E, Vely F, Saint-Laurent N, Pradayrol L, Buscail L, Susini C.

Institut National de la Sante et de la Recherche Medicale U531, IFR31, CHU Rangueil, 31403 Toulouse, France.

The G protein-coupled sst2 somatostatin receptor acts as a negative cell growth regulator. Sst2 transmits antimitogenic signaling by recruiting and activating the tyrosine phosphatase SHP-1. We now identified Src and SHP-2 as sst2-associated molecules and demonstrated their role in sst2 signaling. Surface plasmon resonance and mutation analyses revealed that SHP-2 directly associated with phosphorylated tyrosine 228 and 312, which are located in sst2 ITIMs (immunoreceptor tyrosine-based inhibitory motifs). This interaction was required for somatostatin-induced SHP-1 recruitment and activation and consequent inhibition of cell proliferation. Src interacted with sst2 and somatostatin promoted a transient Gbetagamma-dependent Src activation concomitant with sst2 tyrosine hyperphosphorylation and SHP-2 activation. These steps were abrogated with catalytically inactive Src. Both catalytically inactive Src and SHP-2 mutants abolished somatostatin-induced SHP-1 activation and cell growth inhibition. Sst2-Src-SHP-2 complex formation was dynamic. Somatostatin further induced sst2 tyrosine dephosphorylation and complex dissociation accompanied by Src and SHP-2 inhibition. These steps were defective in cells expressing a catalytically inactive Src mutant. All these data suggest that Src acts upstream of SHP-2 in sst2 signaling and provide evidence for a functional role for Src and SHP-2 downstream of an inhibitory G protein-coupled receptor.

5 : Proc Natl Acad Sci U S A. 2003 Jan 7 ;100(1):155-60. Epub 2002 Dec 18.

Somatostatin receptor subtype 2 sensitizes human pancreatic cancer cells to death ligand-induced apoptosis.

Guillermet J, Saint-Laurent N, Rochaix P, Cuvillier O, Levade T, Schally AV, Pradayrol L, Buscail L, Susini C, Bousquet C.

Institut National de la Sante et de la Recherche Medicale (INSERM) U531, Institut Federatif de Recherche (IFR) 31, Centre Hospitalier Universitaire (CHU) Rangueil, France.

Somatostatin receptor subtype 2 (sst2) gene expression is lost in 90% of human pancreatic adenocarcinomas. We previously demonstrated that stable sst2 transfection of human pancreatic BxPC-3 cells, which do not endogenously express sst2, inhibits cell proliferation, tumorigenicity, and metastasis. These sst2 effects occur as a consequence of an autocrine sst2-dependent loop, whereby sst2 induces expression of its own ligand, somatostatin. Here we investigated whether sst2 induces apoptosis in sst2-transfected BxPC-3 cells. Expression of sst2 induced a 4.4- +/- 0.05-fold stimulation of apoptosis in BxPC-3 through the activation of tyrosine phosphatase SHP-1. sst2 also sensitized these cells to apoptosis induced by tumor necrosis factor alpha (TNFalpha), enhancing it 4.1- +/- 1.5-fold. Apoptosis in BxPC-3 cells mediated by TNF-related apoptosis-inducing ligand (TRAIL) and CD95L was likewise increased 2.3- +/- 0.5-fold and 7.4- +/- 2.5-fold, respectively. sst2-dependent activation and cell sensitization to death ligand-induced apoptosis involved activation of the executioner caspases, key factors in both death ligand- or mitochondria-mediated apoptosis. sst2 affected both pathways : first, by up-regulating expression of TRAIL and TNFalpha receptors, DR4 and TNFRI, respectively, and sensitizing the cells to death ligand-induced initiator capase-8 activation, and, second, by down-regulating expression of the antiapoptotic mitochondrial Bcl-2 protein. These results are of interest for the clinical management of chemoresistant pancreatic adenocarcinoma by using a combined gene therapy based on the cotransfer of genes for both the sst2 and a nontoxic death ligand.

6 : Cancer Res. 2002 Nov 1 ;62(21):6124-31.

Antitumor effect of in vivo somatostatin receptor subtype 2 gene transfer in primary and metastatic pancreatic cancer models.

Vernejoul F, Faure P, Benali N, Calise D, Tiraby G, Pradayrol L, Susini C, Buscail L.

Institut National de la Sante et de la Recherche Medicale U531, Institut Louis Bugnard IFR31, Centre Hospitalier Universitaire Rangueil, 31403 Toulouse Cedex 4, France.

Our previous studies conducted in pancreatic cancer models established in nude mice and hamsters revealed that cloned somatostatin receptor subtype 2 (sst2) gene expression induced both antioncogenic and local antitumor bystander effects in vivo. In the present study, in vivo gene transfer of sst2 was investigated in two transplantable models of primary and metastatic pancreatic carcinoma developed in hamsters. LacZ reporter or mouse sst2 genes were expressed by means of two different delivery agents : an adenoviral vector and a synthetic polycationic carrier [linear polyethylenimine (PEI)]. sst2 was injected into either exponentially growing pancreatic primary tumors or hepatic metastases, and then transgene expression and tumor progression were investigated 5-6 days after gene transfer. Molecular mechanisms involved in the inhibition of tumor growth were also analyzed. Both adenovirus- and PEI-mediated in vivo gene transfer in primary pancreatic tumors induced an increase of beta-galactosidase activity and expression of sst2 transgene nRNA (100% and 86% of tumors for adenovirus and PEI vector, respectively). Adenoviral vector-based sst2 gene transfer resulted in significant reduction of pancreatic tumor growth (P < 0.05). Using PEI vector, both pancreatic primary tumor growth and metastatic tumor growth were also significantly slackened as compared with both LacZ-treated and untreated control groups (P < 0.02). Moreover, the proliferative index decreased significantly (P < 0.005), whereas apoptosis increased (P < 0.005) in tumors transferred with sst2 gene. The increase of apoptosis correlated with an activation of the caspase-3 and poly(ADP-ribose) polymerase pathways. We concluded that in both primary and metastatic pancreatic cancer models, the synthetic gene delivery system can achieve in vivo sst2 gene transfer and results in a significant antitumor effect characterized by an increase of apoptosis and an inhibition of cell proliferation. This new strategy of gene therapy allows the restoration of expression of an antioncogenic molecule and could be promising for the treatment of advanced pancreatic cancer.

7 : J Biol Chem. 2002 Oct 25 ;277(43):40375-83. Epub 2002 Aug 12.

A novel protein-protein interaction between a G protein-coupled receptor and the phosphatase SHP-2 is involved in bradykinin-induced inhibition of cell proliferation.

Duchene J, Schanstra JP, Pecher C, Pizard A, Susini C, Esteve JP, Bascands JL, Girolami JP.

INSERM U388, Institut Louis Bugnard, Institute Federatif de Recherche 31, Centre Hospitalier Universitaire Rangueil, 1 Avenue J. Poulhes, 31403 Toulouse Cedex, France.

Mitogenic G protein-coupled receptor (GPCR) signaling has been extensively studied. In contrast, little is known about anti-mitogenic GPCR signaling. We show here that anti-mitogenic signaling of a GPCR, the bradykinin B2 receptor, involves a novel direct protein-protein interaction. The antiproliferative effect of bradykinin was accompanied by a transient increase in protein-tyrosine phosphatase activity. Using surface plasmon resonance analysis, we observed that an immunoreceptor tyrosine-based inhibitory motif (ITIM) located in the C-terminal part of the B2 receptor interacted specifically with the protein-tyrosine phosphatase SHP-2. The interaction was confirmed in primary culture renal mesangial cells by co-immunoprecipitation of a B2 receptor.SHP-2 complex. The extent of the interaction was transiently increased by stimulation with bradykinin, which was accompanied by an increase in specific SHP-2 phosphatase activity. Mutational analysis of the key ITIM residue confirmed that the B2 receptor ITIM sequence is required for interaction with SHP-2, SHP-2 activation, and the anti-mitogenic effect of bradykinin. Finally, in mesangial cells transfected with a dominant-negative form of SHP-2, bradykinin lost the ability to inhibit cell proliferation. These observations demonstrate that bradykinin inhibits cell proliferation by a novel mechanism involving a direct protein-protein interaction between a GPCR (the B2 receptor) and SHP-2.

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