Differential effect of apoptosis‐associated tyrosine kinase on K‐Cl cotransporter activity in C6 glioblastoma cells (694.2)

Abstract

Expression of the potassium‐chloride (K‐Cl) cotransporter is linked to the growth and spread of gynecological cancers. Immunofluorescent localization of three K‐Cl cotransporter isoforms (KCC1, KCC3, and KCC4) to migrating extensions of rat glioblastoma (C6) cells suggests their potential role in the enhanced motility of these tumors. RT‐PCR amplification of mRNA from C6 cells validated the expression of kinases and phosphatases known to control cation‐chloride cotransporter activity. Xenopus laevis oocytes co‐injected with KCC3 and apoptosis‐associated tyrosine kinase (AATYK1) cRNA showed isosmotic K+ influx similar to hyposmotically‐activated K+ influx, whereas no change in isosmotic K+ influx was observed with co‐injection of KCC1 and AATYK1 cRNA. This differential effect of AATYK1 on two KCC isoforms prompted testing of the potential of AATYK1 as a novel target for affecting glioblastoma motility. Genistein, a general tyrosine kinase inhibitor, failed to reduce the hyposmotically‐stimulated K+ influx of C6 cells or inhibit their motility in a scratch wound assay indicating that the catalytic activity of the tyrosine kinase is not involved. Molecular identification of both serine/threonine kinase and phosphatase binding sites on AATYK1 suggests that it may scaffold other K‐Cl cotransporter regulatory proteins and thus represent a novel target for anti‐cancer therapeutics.Grant Funding Source: Supported by a Special Projects Grant from the University of Saskatchewan College of Medicine