Gamma-glutamyltransferase activity, genes transcripts and differentiation by all-trans retinoic acid have been investigated in cultured HL-60, U937 and K562 cells. Acquisition of morphological and functional characteristics confirmed the terminal differentiation of HL-60 and U937 cells. All-trans r retinoic acid increased gamma-glutamyltransferase activity in a cell type- and time-dependent manner. Treatments with all-trans retinoic acid isomers and structurally analogs showed that only retinoids with carboxylic acid group were able to induce enzyme activity in terminal differentiated cells. Additionally, the analysis of gamma-glutamyltransferase genes transcription products demonstrated clearly that, both in untreated and in RA treated cells, only mRNA type I transcribed from the gene 6, was expressed.
