N-GLYCOSYLATION OF THE HUMAN GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR-RECEPTOR ALPHA-SUBUNIT IS ESSENTIAL FOR LIGAND-BINDING AND SIGNAL-TRANSDUCTION

The alpha subunit of the receptor for human granulocyte-macrophage col ony-stimulating factor (GM-CSF) is a glycoprotein containing 11 potent ial N-glycosylation sites in the extracellular domain, We examined the role of N-glycosylation on alpha subunit membrane localization and fu nction, Tunicamycin, an N-glycosylation inhibitor, markedly inhibited GM-CSF binding, GM-CSF-induced deoxyglucose uptake, and protein tyrosi ne phosphorylation in HL-60(eos) cells but did not affect cell surface expression of the alpha subunit as detected by an anti-alpha subunit monoclonal antibody, In COS cells expressing the alpha subunit and tre ated with tunicamycin, N-unglycosylated alpha subunit was expressed an d transported to the cell surface but was not capable of binding GM-CS F. High affinity binding in COS cells expressing both alpha and beta s ubunits was also blocked by tunicamycin treatment. These studies indic ate that N-linked oligosaccharides are essential for alpha subunit lig and binding and signaling by the human GM-CSF receptor.