T Lymphocyte activation results in an increased expression of β-1,4-Galactosyltransferase: Phorbol ester induces a similar enhancement in the absence of mitosis

Abstract

We previously showed that in vitro activated human T lymphocytes expressed increased amounts of β-1,6-branched N-linked oligosaccharides (Lemaire S et al. (1994) J Biol Chem 269: 8069-74), which have been proposed to participate in the regulation of the immune process. In the present paper, we compared the activity and expression of β-1,4-galactosyltransferase (GalT), one of the glycosyltransferases involved in the biosynthesis of these β-1,6-branched N-linked oligosaccharides, before and after in vitro activation of T lymphocytes after a 40 h treatment with a mixture of phorbol 12-myristate 13-acetate and Phaseolus vulgaris lectin. After treatment, the enzymatic activity of the GalT was significantly increased and immunoblot experiments performed with a monoclonal antibody to human GalT showed an increased intensity of the GalT band at 49 kDa, attributable to an enhancement of GalT mRNA level, as shown by Northern blots. However, treatment of the same T-lymphocytes by phorbol ester alone, which is unable to induce mitosis, resulted in a comparable increase of the expression of GalT. Moreover, these phorbol ester-treated T lymphocytes, analysed by flow cytometry exhibited a two-fold increase in the expression of GalT. Finally, confocal fluorescence microscopy performed on all T lymphocytes (treated or not) showed that the flow cytometric signal of GalT originates from intracellular, Golgi-associated antigen only since no surface GalT was detected.