A TRANSMEMBRANE PROTEIN-TYROSINE-PHOSPHATASE CONTAINS SPECTRIN-LIKE REPEATS IN ITS EXTRACELLULAR DOMAIN

We report the first chicken transmembrane protein-tyrosine phosphatase , ChPTP lambda, isolated from a brain cDNA library and preB cells. ChP TP lambda has transcripts of about 5.6 kilobases and is abundant in sp leen, intestine, and fibroblasts transformed by oncogenic ras or erbA/ B. It has five alternative splicing products varying near their amino termini, and the largest one contains 1237 amino acids. The extracellu lar domain of ChPTP lambda has several features including a Ser/Thr/Pr o-rich region, one fibronectin type III module, and spectrin-like repe ats (the first case that spectrin-like repeats were found in the non-c ytoplasmic compartment). These repeats were also found in other phosph atases, including CD45 and yeast acid phosphatases PHO5 and PHO3. Anti bodies to ChPTP lambda recognized several protein species whose M(r) r ange from 170,000 to 210,000. ChPTP lambda exhibited phosphotyrosine-s pecific phosphatase activity. Since CD45 also has these features in th e extracellular domain and the two protein-tyrosine phosphatases share 70% similarity in the intracellular domains, we propose that ChPTP la mbda and CD45 belong to the same gene family.