CLONING, EXPRESSION, AND CHROMOSOME MAPPING OF HUMAN GALECTIN-7

The galectins are a family of beta-galactoside-binding proteins implic ated in modulating cell-cell and cell-matrix interactions, Here we rep ort the cloning and expression of a novel member of this family (galec tin-7) that correspond to IEF (isoelectric focusing) 17 (12,700 Da; pI , 7.6) in the human keratinocyte protein data base, and that is striki ngly down-regulated in SV40 transformed keratinocytes (K14). The cDNA was cloned from a lambda gt11 cDNA expression library using degenerate d oligodeoxyribonucleotides back-translated from an IEF 17 peptide seq uence. The protein encoded by the galectin-7 clone comigrated with IEF 17 as determined by two-dimensional (two-dimensional gel electrophore sis) analysis of proteins expressed by transiently transfected COS-1 c ells, and bound lactase. Alignment of the amino acid sequences with ot her members of the family showed that the amino acids central to the b eta-galactoside interaction are conserved. Galectin-7 was partially ex ternalized to the medium by keratinocytes although it has no typical s ecretion signal peptide. Immunoblotting as well as immunofluorescence analysis of human tissues with a specific galectin-7 antibody revealed a narrow distribution of the protein which was found mainly in strati fied squamous epithelium. The antigen localized to basal keratinocytes , although it was also found, albeit at lower levels, in the suprabasa l layers where it concentrated to areas of cell to cell contact, Both, its cellular localization as well as its striking down-regulation in K14 keratinocytes imply a role in cell-cell and/or cell-matrix interac tions necessary for normal growth control. The galectin-7 gene was map ped to chromosome 19.