Interaction of folate receptor with signaling molecules lyn and G alpha(i-3) in detergent-resistant complexes from the ovary carcinoma cell line IGROV1

Using as a model the ovary carcinoma cell line IGROV1, we analyzed the part itioning of the glycosylphosphatilylinositol-anchored folate receptor into lipid rafts based on its relative detergent insolubility, with a focus on p hysically and functionally associated signaling molecules. A variable amoun t (40-60%) of folate receptor was found in lo cv-density Triton X-100 insol uble complexes together with subunits of heterotrimeric G-proteins and the src-family non-receptor tyrosine kinases p53-56 lyn. In the same fraction t he structural component of caveolae, caveolin, was not detected at the prot ein level? although the corresponding mRNA was detected in trace amounts. C omodulation of folate receptor and signalling molecules was observed in the detergent-insoluble complexes during cell proliferation or induced by phos phatidylinositol-specific phospholipase C treatment or by interaction with anti-folate receptor monoclonal antibodies. Moreover, complexes of folate r eceptor, lyn and the G alpha(i-3) subunit were immunoprecipitated using eit her anti-folate receptor or anti-lyn antibodies. In vitro kinase assay of t he immunoprecipitates revealed stimulation of phosphorylation of common and specific proteins. In particular, the p53 form of lyn appeared to be enric hed and phosphorylated in the anti-folate receptor MOv19 monoclonal antibod y immunoprecipitate, whereas a 40 kDa band common to anti-folate receptor a nd anti-lyn immunoprecipitates was the phosphorylated form of the G alpha(i -3) subunit. These findings point to the functional interaction between fol ate receptor and signaling molecules.