Binding of the CXC chemokine, melanoma growth stimulatory activity (MGSA), to the class II IL-8 receptor on cells which overexpress this G-protein coupled receptor results in enhanced phosphorylation on serine residues. In experiments described herein, it is demonstrated that MGSA also enhances the tyrosine phosphorylation of two endogenously tyrosine phosphorylated proteins approximately 130 and 70 kDa in size. MGSA treatment (5 nM) of the clonally selected, stably transfected placental cell line, 3ASubE P-3, which overexpresses the class II IL-8 receptor, results in the maximal tyrosine phosphorylation of the 130 kDa protein before 2 min. This enhanced phosphorylation of the 130 kDa protein returns to basal level after a 5 min treatment. Based upon cell fractionation studies, the 130 kDa protein is concentrated in the membrane fraction of the cells. The 70 kDa protein which also shows tyrosine phosphorylation is predominantly cytosolic. The identity of the 130 kDa tyrosine phosphorylated protein was determined by immunoprecipitation and Western blot analyses. In these experiments, the 130 kDa tyrosine phosphorylated protein was shown to immunoprecipitate with antibody to the cas antigen (crk-associated substrate) and with antibody to the p130 tyrosine phosphorylated protein described as undergoing tyrosine phosphorylation in src transformed cells. The data suggest that MGSA binding to the class II IL-8 receptor is associated with tyrosine phosphorylation of p130/cas. The data also suggest that p130 and the cas antigen are the same protein.