MAZ, A MYC-ASSOCIATED ZINC-FINGER PROTEIN, IS ESSENTIAL FOR THE ME1A1-MEDIATED EXPRESSION OF THE C-MYC GENE DURING NEUROECTODERMAL DIFFERENTIATION OF P19 CELLS

To investigate whether MAZ (Myc-associated zinc finger protein) affect s the expression of the c-myc gene during the retinoic acid-induced (R A-induced) neuroectodermal differentiation of P19 embryonal carcinoma (EC) cells, we introduced a CAT reporter construct, human c-myc promot er/CAT (pMyc2CAT), and a mutant CAT derivative that lacked an ME1a1 si te (pMyc1CAT) into P19EC cells tp monitor the promoter activity of the c-myc gene, The expression of CAT in pMyc2CAT-transformed cells decli ned fivefold after 24 h in the presence of RA, returned to the normal level within 48 h, and decreased again to below 20% of the normal leve l after 96 h. By contrast, the expression of CAT in pMyc1CAT-transform ed cells did not return to the normal level after 48 h in the presence of RA, In addition, an electrophoretic mobility shift assay (EMSA) wi th ME1a1 DNA as probe demonstrated that the kinetics of the DNA-bindin g activity of MAZ were closely correlated with the changes in the expr ession of CAT from the c-myc promoter/CAT gene during the differentiat ion of P19EC cells, Taken together, these results suggest that MAZ pla ys a key role in the transient increase in the expression of the c-myc gene after 48 h of exposure to RA during the neuroectodermal differen tiation of P19EC cells.