Stimulation of tyrosine phosphatase and inhibition of cell proliferation by somatostatin analogues: mediation by human somatostatin receptor subtypes SSTR1 and SSTR2.

Abstract

The effects of s analgus RC-160and SMS-201-995 on tyrosine phosphatase and cell proliferation were investigated in COS-7 and NIH 3T3 cells expressing human somatostatin receptor subtype 1 or 2 (SSTR1 or SSTR2 antagonize the mitogenic effect of growth factors acting on tyrosine kinase receptors such as epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) (9-11). Furthermore, these analogues have been found to stimulate tyrosine phosphatase activity in normal and tumoral pancreatic cells (9,(12)(13)(14)(15) and to activate the dephosphorylation of EGF receptor (9, 16). The ability of somatostatin analogues to stimulate tyrosine phosphatase correlates with their inhibitory effect on pancreatic cell growth, and this correlation supports the hypothesis that the growth inhibition is mediated by dephosphorylation of tyrosine protein signals. Somatostatin analogues might suppress tumor growth by reversing the stimulatory effect of EGF on phosphorylation of EGF receptor tyrosine kinase and EGF-phosphorylated proteins (17). We also observed that a membrane tyrosine phosphatase is coeluted with somatostatin receptor, suggesting that tyrosine phosphatase may be a part ofthe signal transduction pathway promoted by somatostatin receptor occupancy (16).The somatostatin receptor subtypes and the molecular mechanism involved in the tyrosine phosphatase stimulation have been, until now, unknown (18, 19). We must better understand what physiological response every subtype elicits, how their signals are processed in the cell, and in what normal and/or pathological tissues each is expressed to choose the appropriate analogue for targeting to specific cells for therapeutic use.In the present study, we examined the effects of two somatostatin analogues, RC-160 and SMS, on binding and signal transduction pathways of the two human cloned somatostatin receptor subtypes hSSTR1 and hSSTR2 transiently expressed in COS-7 cells. We also investigated the 2315The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Novel synergistic mechanism for sst2 somatostatin and TNFα receptors to induce apoptosis: crosstalk between NF-κB and JNK pathways

“…11 We therefore investigated whether sst2 induces cell death in this previously described and characterized model. 11,12 We quantified apoptosis by using the terminal deoxynucleotidyltransferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL) technique. After 5-h cell serum starvation, apoptosis in sst2-expressing cells was 3.6-71.2-fold higher than in mock cells (5.670.8 versus 1.570.5% of apoptotic cells, respectively) ( Figure 1a).…”

“…Murine fibroblastic NIH3T3 cells were transfected either with the human 1.35-kbp sst2 cDNA (NIH3T3/sst2 cells (clone 2/5 11 ), NIH3T3/sst2.1 cells (clone 2/1 11 )), or with the mock vector (mock cells), and cultured as previously described. 11,12 Cells were treated with 10 ng/ml TNFa (Preprotech Inc.) in the presence of 10 mg/ml of cycloheximide (Sigma). For experiments involving specific inhibitors, cells were pretreated for 1 h with 10 mM DEVD-CHO or IETD-CHO (BIOMOL), 25 mg/ml SN50 or SN50M (SN50Mutated) (BIOMOL), 10 mM Helenalin (BIOMOL), 10 mM SP600125 (BIOMOL), or with 10-50-100 nM BIM23627 (Biomeasure).…”

The Tyrosine Phosphatase SHP-1 Associates with the sst2 Somatostatin Receptor and Is an Essential Component of sst2-mediated Inhibitory Growth Signaling

“…Although the molecular events leading to the inhibition of cell proliferation are still poorly understood, it has been shown that, after binding to somatostatin receptors, somatostatin analogues cause a rapid stimulation of a membrane proteintyrosine phosphatase (PTPase) 1 activity and dephosphorylate phosphorylated epidermal growth factor receptors (9,11,12) suggesting that a PTPase may participate in the somatostatininduced inhibition of growth factor-mediated mitogenic signal. Recently, the expression of the sst2 somatostatin receptor subtype in NIH3T3 and Chinese hamster ovary (CHO) cells led us to the demonstration of the direct involvement of sst2 in both the antiproliferative effect of somatostatin and its stimulatory effect on PTPase activity (13,14). Incubation of cells expressing sst2 with the PTPase inhibitor, vanadate, prevented both effects suggesting that a PTPase may be implicated in the negative growth signal induced by activation of sst2.…”

Somatostatin receptor subtype mRNA expression in human colorectal cancer and normal colonic mucosae

“…All appear to be linked to the inhibition of adenyl cyclase (Patel et al, 1994), but this pathway does not appear to be of primary importance in the antiproliferative activity of somatostatin. Both hSSTR2 and hSSTR1 exhibit growthinhibitory effects via tyrosine phosphatases in vitro (Leibow et al, 1989;Todisco et al, 1994;Buscail et al, 1994) and, hence, can directly antagonize the effects of growth factors, such as EGF (Vidal et al, 1994). hSSTR5 is also linked to the inhibition of proliferation in vitro, although the mechanism appears to be the inhibition of intracellular calcium mobilization (Buscail et al, 1995).…”

“…Somatostatin was initially isolated as a growth hormone release-inhibiting factor and has subsequently been found to be a pan-inhibitory peptide, which inhibits proliferation in a wide variety of cell types, even following malignant transformation (Patel et al, 1981). There is evidence that this antiproliferative activity may be caused by a number of mechanisms, including inhibition of release of stimulatory systemic hormones and growth factors (Patel et al, 1981), inhibition of angiogenesis (Woltering et al, 1990), immunomodulation (Partsch et al, 1992) and direct action through high-affinity, cell-surface receptors (Pagliacci et al, 1991;Buscail et al, 1994). Five highaffinity, cell-surface somatostatin receptors of the seven-transmembrane, G-protein-coupled type have been identified and their genes sequenced (Yamada et al, 1992a(Yamada et al, , b, 1993Rohrer et al, 1993;O'Carroll et al, 1993).…”