A novel protein-tyrosine phosphatase related to the homotypically adhering κ and μ receptors

Abstract

Here we describe a novel member of the receptor-like protein-tyrosine phosphatases (PTPs) termed PTP λ, which is homologous to the homotypically adherent PTPs κ and μ. Murine PTP λ contains MAM, IgG, fibronectin type III, and dual phosphatase domains. As has been demonstrated for PTPs κ and μ, PTP λ mediates homotypic adhesion in vitro, and PTP λ is associated with β catenin in kidney epithelial cells. The extracellular domain of PTP λ is proteolytically processed in cell culture as well as in vivo. Northern blot analysis reveals that PTP λ is expressed throughout embryonic development and is predominately found in adult brain, lung, and kidney. In situ hybridization to 15.5-day old rat embryos reveals that PTP λ is expressed in a variety of embryonic neuronal sites as well as in the esophagus, lung bronchiolar epithelium, kidney glomerular epithelium, olfactory epithelium, and various cartilagenous sites. Analysis of neonatal brain demonstrates expression in cells of the hippocampus, cortex, 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.