Macrophage-Stimulating Protein Activates Ras by both Activation and Translocation of SOS Nucleotide Exchange Factor

Abstract

Macrophage-stimulating protein (MSP) is a chemotactic factor that activates the receptor tyrosine kinase RON. The involvement of Ras in MSP-induced signal transduction was investigated. Here we demonstrate that, in RON-transfected MDCK cells, an active GTP-bound form of Ras was rapidly accumulated by MSP treatment and the Ras-guanine nucleotide exchange activity in SOS immunoprecipitates was concomitantly increased. GAP activity was not changed under the same conditions used. Furthermore, the SH2 domain of adaptor protein GRB2, but not Shc, associated with the activated RON-beta chain, and GRB2-SOS complexes translocated from the cytosol to the membrane upon MSP treatment. These results strongly suggest that MSP activates Ras through RON, and that MSP-induced activation of Ras might be controlled by both the enhancement of catalytic exchange activity of SOS and its translocation to the membrane where its target Ras is localized.

Isoform-specific insertion near the Grb2-binding domain modulates the intrinsic guanine nucleotide exchange activity of hSos1

“…In that regard, it is interesting to note recent reports (Li et al, , 1993a(Li et al, , 1995(Li et al, , 1996 suggesting that, in contrast to the currently prevailing translocation model (reviewed in Schlessinger 1993;Downward 1994), an increase in the intrinsic catalytic activity of Sos1 may suce to account for the activation of Ras by some tyrosine kinase receptors including NGF, EGF, PDGF and macrophage-stimulating protein receptor. Indeed, our direct comparison of the Ras guanine nucleotide exchange (GEF) activity detectable in lysates of transfected cells overexpressing Isf I and Isf II con®rmed that view.…”

“…In support of this notion, constitutive or conditional membrane targeting of these exchange factors has been shown to potentiate Ras activation in transfected cells (Aronheim et al, 1994;Quilliam et al, 1994;Holsinger et al, 1995). However, some recent reports suggest that, irrespective of subcellular location, the intrinsic guanine nucleotide releasing activity of Sos may be dierent before and after stimulation of surface tyrosine kinase receptors (Li et al, 1993a(Li et al, , 1995(Li et al, , 1996. Such a notion would be consistent with other reports suggesting that the Cterminal portion of Sos may exert negative regulation over the activity of the whole Sos1 protein (Aronheim et al, 1994;Quilliam et al, 1994;Karlovich et al, 1995;McCollam et al, 1995;Wang et al, 1995;Byrne et al, 1996;Corbalan-Garcia et al, 1998).…”

c-Cbl is a critical modulator of the Ron tyrosine kinase receptor

“…The multifunctional docking site of Ron interacts with the SH2 domain of Grb2 (Li et al, 1995), an adaptor protein involved in the recruitment of c-Cbl to RTKs (Peschard et al, 2001;Waterman et al, 2002), through its SH3 domains (Meisner et al, 1995). We verified whether the disruption of the interaction either between Grb2 and c-Cbl, by inactivating Grb2 SH3 domains (W 36, 193 K), or between Ron and Grb2, by using the SH2-impaired Grb2 mutant (R 86 K), was sufficient to abrogate Ron/Cbl association (Figure 6c).…”

Collaborative activities of macrophage-stimulating protein and transforming growth factor-β1 in induction of epithelial to mesenchymal transition: roles of the RON receptor tyrosine kinase

“…MSP belongs to the kringle protein family that includes plasminogen, HGF, and others (Gherardi et al, 1997). Activation of RON by MSP stimulates multiple signaling pathways including Ras (Li et al, 1995), PI-3 kinase (Wang et al, 1996a), MAP kinase (Santoro et al, 1998), and NFkB (Zhou et al, 2002). These pathways regulate a variety of cellular activities in different types of cells .…”