Different molecular forms of a glycoprotein antigen found on azurophilic granule membranes of cultured human HL60 promyelocytes and on the plasma membrane of a myeloblastoid variant line

In previous immunohistological studies an antigen designated D46 was identified on the surface of an agranular, myeloblastoid cell line (HL60-D). It was not detected on the surface of either parental HL60 cells or variants with aberrant primary granules (HL60-A7). In these promyelocytes it was found to be intracytoplasmic, in a granular pattern. In the work presented here, this antigen and other granule-related glycoproteins were studied by radiolabeling, subcellular fractionation and gel electrophoresis. The major findings include the following: (1) the anti-D46 antibody precipitated one major and one minor glycosylated component, each of which migrated with a different electrophoretic mobility, depending on whether it was derived from cells with or without granules. Incorporation of radioactive amino acids, but not monosaccharides, revealed an additional component of lower mobility. (2) The D46 antigen(s) was recovered in the detergent-rich phase of a Triton X-114 extract of granules, suggesting that it is an integral membrane protein. (3) As assessed by the relative activities of marker enzymes, the granules of both the HL60 and HL60-A7 cell lines exhibited a heterogeneous pattern of sedimentation in density gradients. (4) The electrophoretic patterns of the major [2- 3H]mannose-labeled glycoproteins of the granule-enriched fractions were similar, except for one diffuse band of 110–170 kD which was not detected in HL60-A7. These studies provide direct evidence for heterogeneity of enzymatic and membrane constituents of primary myeloid granules, and give the first indication that there may be glycoprotein changes associated with certain ultra-structural defects that occur in abnormal promyelocytes. They suggest also, in the example of the D46 antigen, that some glycoproteins may exist in different forms when localized to either the granules or the plasma membrane.