Tyrosine phosphorylation of a 120-kilodalton pp60src substrate upon epidermal growth factor and platelet-derived growth factor receptor stimulation and in polyomavirus middle-T-antigen-transformed cells.

Abstract

The monoclonal antibody 2B12 is directed toward p120, a 120-kDa cellular protein originaUly identified as a protein tyrosine kinase substrate in cells expressing membrane-associated oncogenic variants of pp6(Yrc. In this report, we show that p120 was tyrosine phosphorylated in avian cells expressing membrane-associated, enzymatically activated variants of c-src, including variants having structural alterations in the src homology regions 2 and 3. In contrast, p120 was not tyrosine phosphorylated in cells expressing enzymatically activated, nonmyristylated pp60'. Furthermore, p120 was tyrosine phosphorylated in avian ceUls expressing middle T antigen, the transforming protein of polyomavirus, as weUl as in rodent cells stimulated with either epidermal growth factor (EGF) or platelet-derived growth factor. Analysis of the time course of p120 tyrosine phosphorylation in EGF-stimulated cells revealed a rapid onset of tyrosine phosphorylation. In addition, both the extent and duration of p120 phosphorylation increased when cells overexpressing the EGF receptor were stimulated with EGF. Biochemical analysis showed that p120 (in both normal and src-transformed cells) was membrane associated, was myristylated, and was phosphorylated on serine and threonine residues. Hence, p120 appears to be a substrate of both nonreceptor-and ligand-activated transmembrane receptor tyrosine kinases and of serine/threonine kinases and is perhaps a component of both mitogen-stimulated and tyrosine kinase oncogene-induced signaling pathways.

The regulatory or phosphorylation domain of p120 catenin controls E-cadherin dynamics at the plasma membrane

“…Using these phospho-specific p120 antibodies, we showed that T310 and T916 of p120 are specifically phosphorylated when cadherins are expressed in cadherin deficient MiaPaCa-2 cells. This is in agreement with results from others showing that serine/threonine residues of p120 are constitutively phosphorylated in many different cell lines including MDCK, MCF-7, HCT-116, and A431 [16,32,40,41]. Each of these cell lines expresses functional cadherins that are localized at the cell surface.…”

Overexpression of leucocyte common antigen (LAR) P-subunit in thyroid carcinomas

“…Loss of these molecules has been correlated with increased tumour invasiveness and change in phenotype (Bukholm et al, 1998). Such molecules, including p120, catenin, E-cadherin, gcatenin (plakoglobin) and b-catenin, are apparently regulated by tyrosine phosphorylation (Kanner et al, 1991;Hinck et al, 1994;Xu and Carpenter, 1999). LAR expression was evidently regulated by contact inhibition via E-cadherin-dependent cell -cell communication in an in vitro study (Symons et al, 2002).…”

p120ctn Binds to the Membrane-proximal Region of the E-cadherin Cytoplasmic Domain and Is Involved in Modulation of Adhesion Activity

“…ctn was originally described as a substrate for activated Src and is also tyrosine-phosphorylated following the stimulation of cells with growth factors, such as epidermal growth factor (27)(28)(29), but it has also been shown to be constitutively phosphorylated on serine/threonine residues in several cell lines (29,30). Therefore, we were interested in determining whether or not a change in the phosphorylation level of p120 ctn has some effect on the activity of the E⌬C71 protein expressed on L cells.…”

“…p120 ctn was first discovered as a protein the phosphorylation of which on tyrosine residues was correlated with transformation in cells transfected with pp60 v-Src (27). p120 ctn is also tyrosine-phosphorylated following the stimulation of cells by growth factors, epidermal growth factor, colony-stimulating factor, and platelet-derived growth factors (28,29). In addition to phosphorylation on tyrosine residues in transformed cells and in response to growth factors, constitutive phosphorylation of p120 ctn on serine and to a lesser extent on threonine residues in both normal and src-transformed cells was noticed (29).…”

“…p120 ctn is also tyrosine-phosphorylated following the stimulation of cells by growth factors, epidermal growth factor, colony-stimulating factor, and platelet-derived growth factors (28,29). In addition to phosphorylation on tyrosine residues in transformed cells and in response to growth factors, constitutive phosphorylation of p120 ctn on serine and to a lesser extent on threonine residues in both normal and src-transformed cells was noticed (29). It was also shown that in Madin-Darby canine kidney cells, p120 ctn is phosphorylated primarily on serine residues, with some phosphothreonine but no detectable phosphotyrosine (30).…”