ALTERATIONS OF DIFFERENTIATION, CLONAL PROLIFERATION, CELL-CYCLE PROGRESSION AND BCL-2 EXPRESSION IN RAR-ALPHA-ALTERED SUBLINES OF HL-60

All-trans retinoic acid (RA) induces granulocytic differentiation of a cute promyelocytic leukemia cells both in vivo and in vitro. In the HL -60 wild-type (WT) early promyelocytic leukemia cell line, granulocyti c differentiation appears to be directly mediated by the nuclear recep tor RAR alpha. An HL-60 subline resistant to RA (HL-60 R) contains a p oint mutation which results in a truncation of 52 amino acids at the C OOH end of RAR alpha. Cross-talk between differentiation, clonal inhib ition of growth and apoptosis was studied using HL-60 WT, HL-60 R, and HL-60 R infected by a retroviral vector containing RAR alpha (LX) as targets, which were cultured with various retinoids, vitamin D-3 analo gs, HMBA, or DMSO. None of these compounds induced significant differe ntiation of HL-60 R and HL-60 LX, but they did induce differentiation of HL-60 WT. In contrast, retinoids inhibited the clonal proliferation of HL-60 WT, HL-60 R, and HL-60 LX. Vitamin D-3 analogs including KH1 060 stimulated the clonal growth of HL-60 R; but they inhibited clonal growth of HL-60 WT and LX. Levels of Bcl-2 strongly decreased in HL-6 0 WT and LX after treatment by retinoids, while no change in expressio n occurred in HL-60 R. Neither KH 1060 nor 9-cis RA induced apoptosis of HL-60 R, but these agents did induce apoptosis in HL-60 LX WT. Take n together, we showed that HL-60 R has a global defect in its ability to be induced to differentiate by a variety of pathways, not merely th e retinoid pathway. Furthermore, our HL-60 models showed that inhibiti on of proliferation and induction of apoptosis and differentiation can be dissociated. Clinically, these results suggest that several putati ve differentiation agents may have anti-cancer (antiproliferative) act ivities, even though they do not induce differentiation of the cancer cells.