1,3-L-Fucosyltransferase Expression in Developing Human Myeloid Cells

In an attempt to correlate the cell surface expression of Le and sialyl-Le structures in immature and mature myeloid cells with the genes expressing α1,3-fucosyltransferase(s) we have examined: 1) the properties of the cellular α1,3-fucosyltransferases and the mRNA transcripts corresponding to the five cloned genes, Fuc-TIII, Fuc-TIV, Fuc-TV, Fuc-TVI, and Fuc-TVII, in mature granulocytes and in the myeloid cell line HL-60, before and after dimethyl sulfoxide-induced differentiation and 2) the properties of the α1,3-fucosyltransferases expressed in COS-7 cells transfected with plasmids containing Fuc-TIV and Fuc-TVII cDNAs. The previously shown increase in cell surface expression of sialyl-Le on differentiation of HL-60 cells (Skacel P. O., Edwards A. J., Harrison C. T., and Watkins W. M.(1991) Blood 78, 1452-1460) is accompanied by a sharp fall in expression of Fuc-TIV mRNA and a persistence of expression of Fuc-TVII mRNA. The properties of the α1,3-fucosyltransferase expressed in COS-7 cells transfected with Fuc-TIV are consistent with this being the major gene responsible for the expression of Le in the immature myeloid cells. In Northern blot analyses, no transcripts of Fuc-TIII, Fuc-TV, or Fuc-TVI were detected in total RNA from mature granulocytes or mRNA from HL-60 cells before or after differentiation. In total RNA from mature granulocytes, Fuc-TIV transcripts were only faintly visible, whereas Fuc-TVII transcripts were quite definitely expressed. The specificity properties of Fuc-TVII expressed in COS-7 cells are consistent with this gene being the major candidate α1,3-fucosyltransferase controlling the expression of sialyl-Le on mature cells. However, Le continues to be expressed on the surface of mature granulocytes and cell extracts retain the capacity to transfer fucose to non-sialylated acceptor substrates. The question therefore remains as to whether these properties result from the weakly expressed Fuc-TIV gene or whether another α1,3-fucosyltransferase gene remains to be identified.