We developed a system to study the function of the ectodomain of RPTPα, a transmembrane protein-tyrosine phosphatase, by fusing the HA-epitope tagged ectodomain of RPTPα to the transmembrane and intracellular domain of the epidermal growth factor receptor, EGFR, a receptor protein-tyrosine kinase that is activated by dimerization. Although the use of chemical crosslinkers shows that preformed HARPTPα–EGFR dimers exist, bivalent anti-HA-tag antibody activated HARPTPα–EGFR chimeras, suggesting this system may be used to study regulation of dimerization. We used this system to show that newborn calf serum may contain (a) potential ligand(s) for RPTPα. Our results suggest that RPTPα dimerization and thus activity may be affected by ligand binding.
