Human papillomavirus type 16 P₆₇₀ promoter is negatively regulated by CCAAT displacement protein

Abstract

HPV16 late gene transcription from P₆₇₀ is suppressed in undifferentiated keratinocytes. To identify DNA sites involved in the negative regulation, we examined the effect of a series of substitutions in the P₆₇₀ promoter region (nucleotide (nt) 106–855) on the transcription, using an expression plasmid having the promoter fragment placed to drive the firefly-luciferase gene. Twenty-base pair-long segments covering the entire promoter region were replaced with a sequence lacking any so far known factor-binding motifs to produce 38 mutants. These plasmids were introduced by transfecton into undifferentiated or partially differentiated human HaCaT and HeLa cells, and transient expression of the reporter was examined with the cell extracts. The reporter expression from the wild-type promoter region was lower, half to one-third, in the undifferentiated cells than in the partially differentiated cells, which expressed hSkn-1a, a keratinocyte specific transcription factor that activates P₆₇₀, and CCAAT displacement protein (CDP), a transcriptional repressor involved in cell differentiation. Two mutants with substitutions including the putative CDP-binding sites, one from nt 562 to 567 and the other from nt 673 to 678, induced markedly enhanced reporter expression particularly in the partially differentiated cells. Electrophoretic mobility shift analysis demonstrated that bacterially produced GST-CDP bound to the two sites in a sequence-specific manner. The data strongly suggest that CDP acts as a major suppressor for P₆₇₀ transcription by binding to the promoter region in the undifferentiated cells and even in the partially differentiated cells that express the activator hSkn-1a.