Role of Carbohydrate in the Function of Human Granulocyte-Macrophage Colony-Stimulating Factor

CDNA clones for the human hematopoietic regulator granulocyte-macrophage colony-stimulating factor (hGM-CSF) were isolated from a λgt11 cDNA library prepared from RNA of COS cells transiently expressing the gene for hGM-CSF. As the RNA was a rich source of hGM-CSF mRNA, approximately 0.1% of the clones of this library contained hGM-CSF sequences. All of the clones analyzed were full length and were correctly processed. When subcloned into an expression vector and transfected into COS cells, the cDNA clones direct the synthesis of higher levels of the growth factor than the gene from which they were derived. The cDNA for native hGM-CSF was used to generate structural mutants which lack N-linked carbohydrate, O-linked carbohydrate, or both. Although the mutant proteins had differing specific activities, the nonglycosylated forms reproduce many, if not all, of the physiologic functions of authentic hGM-CSF. The role of carbohydrate in the secretion and function of hGM-CSF is discussed.