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. ChPTP lambda has transcripts of about 5.6 kilobases and is abundant in spleen, 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 extracellular domain of ChPTP lambda has several features including a Ser/Thr/Pro-rich region, one fibronectin type III module, and spectrin-like repeats (the first case that spectrin-like repeats were found in the non-cytoplasmic compartment). These repeats were also found in other phosphatases, including CD45 and yeast acid phosphatases PHO5 and PHO3. Antibodies to ChPTP lambda recognized several protein species whose M(r) range from 170,000 to 210,000. ChPTP lambda exhibited phosphotyrosine-specific phosphatase activity. Since CD45 also has these features in the extracellular domain and the two protein-tyrosine phosphatases share 70% similarity in the intracellular domains, we propose that ChPTP lambda and CD45 belong to the same gene family.