Oncogenic activation of the PDGF β receptor by the transmembrane domain of p185neu*

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Abstract
We replaced the transmembrane domain of the wild type murine PDGF β receptor with that of p185neu*, the oncogenic form of p185neu, thereby generating a constitutively activated chimeric receptor PR/neu*. Unlike the wild type PDGF β receptor or a chimeric receptor containing the transmembrane domain of wild type p185neu (PR/neu), PR/neu* induced morphologic transformation, focus formation, and tumorigenicity in mouse C127 fibroblasts. Expression of PR/neu* in mouse Ba/F3 hematopoietic cells, which normally depend on IL-3 for survival and sustained proliferation, induced proliferation in the absence of IL-3. The PR/neu chimera conferred limited IL-3-independent growth of Ba/F3 cells. Only PR/neu* and not PR/neu displayed significantly increased levels of phosphotyrosine compared to the wild type PDGF receptor in C127 and Ba/F3 cells. In addition, PR/neu* immune complexes displayed increased levels of kinase activity in vitro compared to immune complexes of the wild type receptor. Furthermore, novel tyrosine phosphorylated proteins of approximately 60 kDa appeared to specifically complex with PR/neu*, suggesting that PR/neu* may activate distinct signaling pathways. We speculate that the p185neu* transmembrane domain in the context of the PDGF β receptor facilitates receptor homodimerization, thereby inducing tyrosine autophosphorylation followed by association with important signaling substrates and transforming activity. Thus, PR/neu* should be a useful reagent for further characterizing activation and signaling mechanisms of the PDGF β receptor.

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