MECHANISMS OF GLUCOCORTICOID RESISTANCE IN HUMAN LEUKEMIC-CELLS - IMPLICATION OF ABNORMAL 90 AND 70 KDA HEAT-SHOCK PROTEINS

The unliganded glucocorticoid receptor is a multi-oligomer complex con sisting of a ligand-binding protein with which two 90 kDa heat shock p roteins (hsp90s) are associated. Upon binding of glucocorticoid to the receptor, the ligand-binding protein, which dissociated from hsp90s, enters the nucleus binds to a specific site in DNA, and thus transmits signal(s). The 70 kDa heat shock protein (hsp70) also works as a mole cular chaperone when the ligand-binding protein enters the nucleus. Re garding the mechanisms of glucocorticoid resistance, a decreased expre ssion of glucocorticoid receptor and a mutant protein with low ligand binding affinity have been reported. In the present study, to address other mechanisms of glucocorticoid resistance, we examined the express ion of hsp90 and hsp70 in addition to the number of glucocorticoid-bin ding sites and their affinity using glucocorticoid-sensitive and -resi stant human leukemic cell lines. We showed that two of nine resistant cell lines with normal glucocorticoid-binding proteins express aberran t hsp90 and extremely low hsp70, while another seven resistant cell li nes had decreased binding sites with normal hsps. These results sugges t that there are at least two independent mechanisms of glucocorticoid resistance in human leukemic cell lines: the decreased ligand-binding sites and the abnormal hsps expression.