The heterogeneous growth cone glycoprotein gp93 is identical to the signal regulatory protein SIRPalpha/SHPS-1/BIT

Growth cone gp93 is a highly heterogeneous membrane glycoprotein with an Mr of about 93 kDa. It was purified from adult rat brain and microsequenced. The sequences of four different peptide fragments of gp93 matched those of the 'signal regulatory protein' SIRPalpha (also known as SHPS-1, BIT or P84), an Ig superfamily member. SIRPalpha contains a cytoplasmic tail that is a tyrosine kinase substrate and binds the protein tyrosine phosphatase SHP-2. SIRPalpha and gp93 also were immunochemically cross-reactive. A PCR strategy was used to determine whether gp93/SIRPalpha heterogeneity in the brain depended upon the presence of different transcripts and, thus, sequence heterogeneity. However, we observed only a single full-length transcript. A short splice variant also was detected. These data identify gp93 as the Ig superfamily member SIRPalpha. Together with our previous results, the data also demonstrate that, in rat brain, gp93/SIRPalpha heterogeneity is the result of differential glycosylation (plus phosphorylation), rather than sequence heterogeneity.