Phosphorylation of Calmodulin by Permeabilized Fibroblasts Overexpressing the Human Epidermal Growth Factor Receptor

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Abstract
Detergent-permeabilized EGFR-T17 fibroblasts, which overexpress the human epidermal growth factor (EGF) receptor, phosphorylate both poly-L-(glutamic acid, tyrosine) and exogenous calmodulin in an EGF-stimulated manner. Phosphorylation of calmodulin requires the presence of cationic polypeptides, such as poly-L-(lysine) or histones, which exert a biphasic effect toward calmodulin phosphorylation. Optimum cationic polypeptide/calmodulin molar ratios of 0.3 and 7 were determined for poly-L-(lysine) and histones, respectively. Maximum levels of calmodulin phosphorylation were attained in the absence of free calcium, and a strong inhibition of this process was observed at very low concentrations (Ki = 0.2 μM) of this cation. The incorporation of phosphate into calmodulin occurred predominantly on tyrosine residue(s) and was stimulated 34-fold by EGF.This work was supported by research grants to A.V. from the Comisión Interministerial de Ciencia y Tecnología (SAF93/392 and SAF96/35) and from the Dirección General de Investigación Científica y Técnica (PR94/343). J.M.-N. is the recipient of a postdoctoral research contract from the Ministerio de Educación y Ciencia.Peer Reviewe
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