The Gain-of-Function Chinese Hamster Ovary Mutant LEC11B Expresses One of Two Chinese Hamster FUT6 Genes Due to the Loss of a Negative Regulatory Factor

The LEC11 Chinese hamster ovary (CHO) gain-of-function mutant expresses an α(1,3)fucosyltransferase (α(1,3)Fuc-T) activity that generates the Le X , sialyl-Le X , and VIM-2 glycan determinants and has been extensively used for studies of E-selectin ligand specificity. In order to identify regulatory mechanisms that control α(1,3)Fuc-T expression in mammals, mechanisms of FUT gene expression were investigated in LEC11 cells and two new, independent mutants, LEC11A and LEC11B. Northern and ribonuclease protection analyses, using probes that span the coding region of a cloned CHO FUT gene, detected transcripts in each LEC11 mutant but not in CHO cells or other gain-of-function CHO mutants that express a different α(1,3)Fuc-T activity. Coding region sequence analysis and α(1,3)Fuc-T acceptor specificity comparisons with recombinant human Fuc-TV and Fuc-TVI showed that the cloned FUT gene is orthologous to the human FUT 6 gene. Southern analyses identified two closely related FUT 6 genes in the Chinese hamster, whose evolutionary relationships are discussed. The blots showed that rearrangements had occurred in LEC11A and LEC11 genomic DNA, consistent with a cis mechanism of FUT6 gene activation in these mutants. By contrast, somatic cell hybrid analyses revealed that LEC11B cells express FUT 6 gene transcripts due to the loss of a trans -acting, negative regulatory factor. Sequencing of reverse transcriptase-polymerase chain reaction products identified unique 5′- and 3′-untranslated region sequences in FUT 6 gene transcripts from each LEC11 mutant. Northern and Southern analyses with gene-specific probes showed that LEC11A cells express only the cg FUT 6A gene (where cg is Cricetulus griseus ), whereas LEC11 and LEC11B cells express only the cg FUT 6B gene. In LEC11A × LEC11B hybrid cells, the cg FUT 6A gene was predominantly expressed, as predicted if a trans -acting negative regulatory factor functions to suppress cg FUT 6B gene expression in CHO cells. This factor is predicted to be a cell type-specific regulator of FUT 6 gene expression in mammals.