Expression of transmembrane protein tyrosine phosphatase gamma (PTPgamma) in normal and neoplastic human tissues.

Aims To establish the conditions for protein tyrosine phosphatase gamma (PTP gamma) detection in paraffin tissues using two antibodies raised against its NH2- (anti-P4) and COOH-termini (gamma TL1); to analyse its expression in normal tissues and to perform an initial screening of neoplastic tissues. Methods and results Membranous and/or cytoplasmic PTP gamma expression was detected in the majority of epithelial cell types and in endocrine cells, with the highest expression in adrenal medulla, endocrine cells of the gastrointestinal tract and pancreatic islets. Both antibodies stained the thyroid follicular epithelium, but only anti-P4 antibody stained the colloid matrix, suggesting shedding/secretion of the PTP gamma extracellular domain. Marked loss of PTP gamma immunoreactivity was detected in subsets of ovarian (21%), breast (56%) and lung (80%) neoplasms. Conversely, cytoplasmic positivity was found in 37% of lymphomas, mainly of high-grade histotypes, while normal lymphocytes were negative. Brain tissue showed PTP gamma expression in a few neuronal and glial elements and PTP gamma was overexpressed in the majority of high-grade astrocytomas. Conclusions We have analysed PTP gamma expression in archival paraffin-embedded tissues for the first time, demonstrating particularly high expression in endocrine cells and both down- and up-regulation in neoplasia, the latter possibly reflecting the undifferentiated state of the neoplastic cells, suggesting a complex role for this phosphatase.