Murine SHP-1 splice variants with altered Src homology 2 (SH2) domains - Implications for the SH2-mediated intramolecular regulation of SHP-1

SRP-1 is a protein-tyrosine phosphatase with two Src homology 2 (SH2) domai ns. These SH2 domains determine which proteins SHP-1 associates with, but t hey 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 correspond ing 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 an alyses detected shape differences between SHP-1 and the active splice varia nt protein deleted of the amino-terminal SH2 domain; i.e. SHP-1 was globula r and resistant to proteolytic digestion, while the splice variant protein was "rod-shaped" and more susceptible to proteolytic digestion.