A NOVEL PROTEIN-TYROSINE-PHOSPHATASE RELATED TO THE HOMOTYPICALLY ADHERING KAPPA-RECEPTORS AND MU-RECEPTORS

Here we describe a novel member of the receptor-like protein-tyrosine phosphatases (PTPs) termed PTP lambda, which is homologous to the homo typically adherent PTPs kappa and mu. Murine PTP lambda contains MAM, IgG, fibronectin type III, and dual phosphatase domains, As has been d emonstrated for PTPs kappa and mu, PTP lambda mediates homotypic adhes ion in vitro, and PTP lambda is associated with beta catenin in kidney epithelial cells. The extracellular domain of PTP lambda is proteolyt ically processed in cell culture as well as in vivo. Northern blot ana lysis reveals that PTP lambda is expressed throughout embryonic develo pment and is predominately found in adult brain, lung, and kidney. In situ hybridization to 15.5-day old rat embryos reveals that PTP lambda is expressed in a variety of embryonic neuronal sites as well as in t he esophagus, lung bronchiolar epithelium, kidney glomerular epitheliu m, olfactory epithelium, and various cartilagenous sites, Analysis of neonatal brain demonstrates expression in cells of the hippocampus, co rtex, and the substantia nigra. Finally, immunohistochemical analysis reveals expression of this PTP on specific neurons of the spinal cord as well as on isolated cortical neurons.