MOLECULAR ANALYSIS OF A POTENTIALLY PHORBOL-REGULATABLE REGION OF THEHUMAN TOPOISOMERASE II-ALPHA GENE PROMOTER

Topoisomerase II alpha (topo II alpha) mRNA was down-regulated to a gr eater extent in 2 human leukemia HL-60 cell lines sensitive to PMA-ind uced terminal differentiation than in their nondifferentiating daughte r lines following exposure to PMA (Cancer Res., 50: 7116-7122, 1990; B iochem. Pharmacol., in press). The sequence of the topo II alpha promo ter (ATG upstream to -650) in all four cell lines was identical to tha t of a human lymphocyte genomic clone and to that of the previously pu blished sequence from a human placenta clone (J. Biol. Chem., 267: 189 61-18965, 1992). Putative transcriptional start sites were identical i n one sensitive/resistant pair. In the other pair, a methylated site w as identified between positions -242 and -580 within the -650 bp promo ter region of the resistant daughter cell only. The identity of the se quence from all four cell lines indicates that mutations in the topo I I alpha gene promoter of PMA-resistant cells cannot explain the absenc e of topo II alpha mRNA down-regulation following PMA treatment. Alter ed methylation patterns may, however, contribute to the reduced decrea se in topo II alpha gene expression in one PMA-resistant line. (C) 199 4 Academic Press, Inc.