The human dbl-proto-oncogene product is a cytoplasmic phosphoprotein which is associated with the cytoskeletal matrix

The translational product of the dbl oncogene is a 66 kDa (p66) protein with no apparent sequence similarity to any of the known oncogene products, whereas the human dbl proto-oncogene encodes a translational product of 115 kDa (p115). We compared proto-dbl p115 and dbl p66 with respect to their subcellular localization, biogenesis and post-translational modifications. Like p66, p115 was found to be a cytoplasmic phosphoprotein present in both cytosol and crude membrane preparations. Membrane fractionation studies revealed that p115 as well as p66 were primarily associated with fractions enriched in plasma membranes, suggesting that this subcellular compartment is a likely site of action of dbl proteins. The membrane-associated forms of p115 and p66 were fairly resistant to solubilization by nonionic detergents, suggesting that dbl proteins associate with the cytoskeletal matrix. p115 was also found to be phosphorylated primarily on serine residues. However, p115 was phosphorylated to a lesser extent as compared to the phosphorylated form of p66. The half-life of proto-dbl p115 was significantly shorter (1 hour) than that of dbl p66 (5-6 h). The higher stability of p66 is likely due to the acquisition of unrelated human sequences and/or to the deletion of the N-terminal region of proto-dbl.