Increased tyrosine phosphorylation in ras transformed fibroblasts occurs prior to manifestation of the transformed phenotype

Transformation suppression by protein tyrosine phosphatase 1B requires a functional SH3 ligand

We have recently shown that protein tyrosine phosphatase 1B (PTP1B) associates with the docking protein p130Cas in 3Y1 rat fibroblasts. This interaction is mediated by a proline-rich sequence on PTP1B and the SH3 domain on p130Cas. Expression of wild-type PTP1B (WT-PTP1B), but not a catalytically competent, proline-to-alanine point mutant that cannot bind p130Cas (PA-PTP1B), causes substantial tyrosine dephosphorylation of p130Cas (F. Liu, D. E. Hill, and J. Chernoff, J. Biol. Chem. 271:31290-31295, 1996). Here we demonstrate that WT-, but not PA-PTP1B, inhibits transformation of rat 3Y1 fibroblasts by v-crk, -src, and -ras, but not by v-raf. These effects on transformation correlate with the phosphorylation status of p130Cas and two proteins that are associated with p130Cas, Paxillin and Fak. Expression of WT-PTP1B reduces formation of p130Cas-Crk complexes and inhibits mitogen-activated protein kinase activation by Src and Crk. These data show that transformation suppression by PTP1B requires a functional SH3 ligand and suggest that p130Cas may represent an important physiological target of PTP1B in cells.

Immunohistochemical staining of ras oncogene product in neoplastic and non-neoplastic mesothelial tissues: immunoreactivity for N-ras and lack of immunohistochemical staining for Ha-ras and K-ras

Immunohistochemical staining of 36 malignant mesotheliomas and 45 cases of non-neoplastic mesothelium including 20 specimens with signs of hyperplasia were investigated using murine monoclonal antibodies directed against p21 ras protein, Ha-ras protein, K-ras protein, and N-ras protein. All cases of non-neoplastic mesothelium and the majority of the malignant mesotheliomas (78 per cent) showed cytoplasmic and often submembranous immunoreactivity in more than 50 per cent of the cells with both the pan-ras and N-ras antibody. No immunoreactivity was observed for Ha- and K-ras. There was no statistically significant difference with respect to immunoreactivity between neoplastic and non-neoplastic mesothelium or between the various mesothelioma subtypes.

Ras is essential for nerve growth factor- and phorbol ester-induced tyrosine phosphorylation of MAP kinases

Treatment of PC12 cells with nerve growth factor (NGF) induces a rapid increase in tyrosine phosphorylation of multiple cellular proteins. Expression of a dominant inhibitory Ras mutant specifically blocked NGF- and TPA-induced tyrosine phosphorylation of two proteins of approximately 42 and 44 kd. Conversely, expression of an oncogenic variant of Ras induced tyrosine phosphorylation of the same 42 and 44 kd proteins. The 44 kd protein was immunoprecipitated with an antibody directed against extracellular signal-regulated kinase 1/mitogen-activated protein kinase (MAPK) and the 42 kd protein comigrated with a 42 kd MAPK, indicating that at least one and probably both Ras-regulated phosphoproteins are MAPKs. In addition, MAPK activation, as measured by in vitro phosphorylation of myelin basic protein, was also regulated by Ras. Ras was not required for NGF-induced activation of Trk or tyrosine phosphorylation of PLC-gamma 1. Thus, NGF-induced tyrosine phosphorylation occurs both prior to and following Ras action, and Ras plays a critical role in the NGF- and TPA-induced tyrosine phosphorylation of MAPKs.