POTENTIATION OF G(I)-MEDIATED PHOSPHOLIPASE-C ACTIVATION BY RETINOIC ACID IN HL-60 CELLS - POSSIBLE ROLE OF G(GAMMA-2)

Differentiated HL-60 cells acquire responsiveness to fMet-Leu-Phe (fMLP), which activates phospholipase C and O-2(-) generation in a pertussis toxin-sensitive manner. Addition of retinoic acid (RA) for the last 24 h during dimethyl sulfoxide (Me(2)SO)-induced differentiation enhanced fMLP dependent signals and interaction between fMLP receptor and G(i). RA modifies both the function and subunit composition of G(i2), the predominant G(i) of HL-60 membranes, as shown by comparing purified G(i2) from membranes of Me(2)SO-treated cells (D-G(i2)) to G(i) from membranes of cells treated with both Me(2)SO and RA (DR-G(i2)). As compared to D-G(i2), DR-G(i2) induced more fMLP binding when added to membranes of pertussis toxin treated HL-60 cells and, in the presence of GTP gamma S, stimulated beta gamma-sensitive phospholipase C in extracts of HL-60 cells to a much greater extent and at lower concentrations. Immunoblots revealed that RA induced expression of the gamma(2) subunit, which was otherwise undetectable in G(i2) purified from HL-60 cells or in HL-60 membranes. Possibly by inducing expression of gamma(2), RA alters two functions of the G(i) beta gamma subunit, modulation of fMLP receptor-G(i2) coupling and activation of the effector, phospholipase C.