IDENTIFICATION OF A VIABILITY DOMAIN IN THE GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR-RECEPTOR BETA-CHAIN INVOLVING TYROSINE-750

The granulocyte/macrophage colony-stimulating factor (GM-CSF) receptor (GMR) is a heterodimeric receptor expressed by myeloid lineage cells, In this study we have investigated domains of the GMR beta-chain (GMR beta) involved in maintaining cellular viability, Using a series of n ested GMR beta deletion mutants, we demonstrate that there are at leas t two domains of GMR beta that contribute to viability signals, Deleti on of amino acid residues 626-763 causes a viability defect that can b e rescued with fetal calf serum (FCS), Deletion of residues 518-626, i n contrast, causes a further decrement in viability that can be only p artially compensated by the addition of FCS, GMR beta truncated proxim al to amino acid 517 will not support long-term growth under any condi tions, Site directed mutagenesis of tyrosine-750 (Y750), which is cont ained within the distal viability domain, to phenylalanine eliminates all demonstrable tyrosine phosphorylation of GMR beta, Cell lines tran sfected with mutant GMR beta (Y750 --> F) have a viability disadvantag e when compared to cell lines containing wild-type GMR that is partial ly rescued by the addition of FCS. We studied signal transduction in m utant cell lines in an effort to identify pathways that might particip ate in the viability signal. Although tyrosine phosphorylation of JAK2 , SHPTP2, and Vav is intact in Y750 --> F mutant cell lines, She tyros ine phosphorylation is reduced, This suggests a potential role for Y75 0 and potentially She in a GM-CSF-induced signaling pathway that helps maintain cellular viability.