Influence of cell differentiation and protein kinase C activation on sub-cellular distribution of beta-N-acetylhexosaminidases of HL 60 cells

There have been several accounts regarding the alterations of the lysosomal enzyme beta-N-acetylhexosaminidase in human leukaemic cells. In addition to Hex A (alpha beta) and Hex B (beta beta) forms, leukaemic cells contain a third isoenzyme displaying many characteristics in common with Hex S, the alpha alpha dimer representing the residual activity in patients with Sandhoff's disease. In the human leukaemic cell line HL 60, A (alpha beta) and S (alpha alpha) are the most abundant forms. Sub-cellular fractionation of HL 60 cells showed that both A and S forms were present in the lysosomal and post-lysosomal fractions, however, a proportion of activity was found to be associated with the plasma membrane. The phorbol ester 12-O-tetra-decanoylphorbol-13-acetate (TPA) exerts complex effects on the physiology of HL 60 cells, leading to cell differentiation along the macrophage pathway and including activation of Protein Kinase C (PKC). In order to assess the extent to which cell differentiation and PKC activation plays a role in modulating the expression of hexosaminidase during cell differentiation, we treated HL 60 cells with TPA and in parallel with the more specific activator of PKC, 1-oleoyl-2-acetyl diglycerol (OAG) which does not cause cell differentiation. We observed that 24 h exposure of HL 60 cells to TPA or OAG produced significant modification of the hexosaminidase isoenzyme pattern of HL 60 cells. The most remarkable effect was seen in both cases in the plasma membrane fraction. Taken together, our results suggest a correlation between hexosaminidase expression and kinase(s) activation.