SIRPalpha1 and SIRPalpha2: their role as tumor suppressors in breast carcinoma cells.
ABSTRACT We have previously reported that expression of SIRPalpha1/SHPS-1 was strongly suppressed in v-Src-transformed cells and its forced expression resulted in the suppression of anchorage-independent growth of the cells [K. Machida, S. Matsuda, K. Yamaki, T. Senga, A.A. Thant, H. Kurata, K. Miyazaki, K. Hayashi, T. Okuda, T. Kitamura, T. Hayakawa, M. Hamaguchi, v-Src suppresses SHPS-1 expression via the Ras-MAP kinase pathway to promote the oncogenic growth of cells, Oncogene 19 (2000) 1710-1718]. We examined the effect of human SIRPalpha1 expression in breast cancer cell lines, Hs578T and MCF7, and compared with the effect of SIRPalpha2 expression in Hs578T. Forced expression of either SIRPalpha1 or SIRPalpha2 did not perturb the growth of Hs578T in a conventional attached condition. Their expression, however, enforced the actin stress fiber formation and induced activation of Rho, but not Rac, in Hs578T cells. Moreover, forced expression of either SIRPalpha1 or SIRPalpha2 displayed distinct suppressive effect on the anchorage-independent growth of Hs578T cells. Similarly, forced expression of SIRPalpha1 in MCF7 specifically suppressed the anchorage-independent growth of the cells. Taken together, our results strongly suggest the function of SIRPalpha1 and 2 as type II tumor suppressors for human breast carcinoma.
- SourceAvailable from: Alexei Kharitonenkov[show abstract] [hide abstract]
ABSTRACT: Phosphotyrosine phosphatases are critical negative or positive regulators in the intracellular signalling pathways that result in growth-factor-specific cell responses such as mitosis, differentiation, migration, survival, transformation or death. The SH2-domain-containing phosphotyrosine phosphatase SHP-2 is a positive signal transducer for several receptor tyrosine kinases (RTKs) and cytokine receptors. To investigate its mechanism of action we purified a tyrosine-phosphorylated glycoprotein which in different cell types associates tightly with SHP-2 and appears to serve as its substrate. Peptide sequencing in conjunction with complementary DNA cloning revealed a new gene family of at least fifteen members designated signal-regulatory proteins (SIRPs). They consist of two subtypes distinguished by the presence or absence of a cytoplasmic SHP-2-binding domain. The transmembrane polypeptide SIRP alpha1 is a substrate of activated RTKs and in its tyrosine-phosphorylated form binds SHP-2 through SH2 interactions and acts as its substrate. It also binds SHP-1 and Grb2 in vitro and has negative regulatory effects on cellular responses induced by growth factors, oncogenes or insulin. Our findings indicate that proteins belonging to the SIRP family generally regulate signals defining different physiological and pathological processes.Nature 04/1997; 386(6621):181-6. · 38.60 Impact Factor
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ABSTRACT: Transformation of cells in tissue culture results in a variety of cellular changes including alterations in cell growth, adhesiveness, motility, morphology, and organization of the cytoskeleton. Morphological and cytoskeletal changes are perhaps the most readily apparent features of transformed cells. Although a number of studies have documented a decrease in the expression of specific tropomyosin (TM) isoforms in transformed cells, it remains to be determined if the suppression of TM synthesis is essential in the establishment and maintenance of the transformed pheno-type. To address the roles of different TM isoforms in transformed cells we have examined the effects of expressing specific TM isoforms in transformed cells using a Kirsten virus-transformed cell line (ATCC NRK1569) as a model system. In contrast to normal fibroblasts, the NRK 1569 cells contain reduced levels of TM-1 and undetectable levels of TM-2 and TM-3. These cells have a rounded morphology and are devoid of stress fibers. Employing expression plasmids for TM-2 and TM-3, stable cell lines were established from the NRK 1569 cells that express these isoforms individually. We demonstrate that expression of TM-2 or TM-3 leads to increased cell spreading accompanied by the formation of identifiable microfilament bundles, as well as significant restoration of well-defined vinculin-containing focal adhesion plaques, although expression of each isoform exhibited distinct properties. In addition, cells expressing TM-2, but not TM-3, exhibited contact-inhibited cell growth and a requirement for serum.Proceedings of the National Academy of Sciences 10/1996; 93(18):9618-23. · 9.74 Impact Factor
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ABSTRACT: To search for the signaling pathway critical for tumor invasion, we examined the effects of dominant negative ras (S17N ras) expression on the activation of matrix metalloproteinase-2 (MMP-2) in src-transformed 3Y1, SR3Y1, under the control of conditionally inducible promoter. In SR3Y1 clones transfected with S17N ras, augmented secretion and proteolytic activation of MMP-2 were dramatically suppressed by S17N Ras expression, while tyrosine phosphorylation of cellular proteins was not suppressed. We found that invasiveness of SR3Y1 cells assayed by the modified Boyden Chamber method was strongly suppressed by S17N Ras expression. In contrast, cell morphology reverted partially and glucose uptake remained unchanged by S17N Ras expression. In addition, treatment of SR3Y1 with manumycin A, a potent inhibitor of Ras farnesyltransferase, strongly suppressed both augmented secretion and proteolytic activation of MMP-2. Contrary, treatment of SR3Y1 with wortmannin or TPA showed no clear effect on MMP-2 activation. Thus, these results strongly suggest that Ras-signaling, but neither P13 kinase- nor protein kinase C-signalings, plays a critical role in activation of MMP-2 and, subsequently, in the invasiveness of src-transformed cells.Oncogene 12/1999; 18(47):6555-63. · 7.36 Impact Factor