Murine SHP-1 splice variants with altered Src homology 2 (SH2) domains. Implications for the SH2-mediated intramolecular regulation of SHP-1.
SHP-1 is a protein-tyrosine phosphatase with two Src homology 2 (SH2) domains. These SH2 domains determine which proteins SHP-1 associates with, but they also autoregulate the activity of the catalytic domain. In this report, we find that the murine SHP-1 transcript is processed to yield a series of alternatively spliced in-frame transcripts, the majority of which exclude exons encoding one or the other SH2 domain. We have examined the corresponding protein isoforms in several ways. First, our measurements of V(max) and K(m) under different conditions indicate that the SH2 variants have elevated activity because of lessened autoregulation. Second, to ascertain whether regulation by the SH2 domains reflects intra- or intermolecular effects, we analyzed the state of SHP-1 by high performance liquid chromatography and sucrose density gradient centrifugation. Our results showed that SHP-1 is a monomer and, thus, is regulated in an intramolecular manner. Third, our analyses detected shape differences between SHP-1 and the active splice variant protein deleted of the amino-terminal SH2 domain; i.e. SHP-1 was globular and resistant to proteolytic digestion, while the splice variant protein was "rod-shaped" and more susceptible to proteolytic digestion.