EVALUATION OF THE ROLE OF AP1-LIKE PROTEINS IN THE ENHANCED APOLIPOPROTEIN-E GENE-TRANSCRIPTION ACCOMPANYING PHORBOL ESTER-INDUCED MACROPHAGE DIFFERENTIATION

Differentiation of THP1 monocytes to a macrophage phenotype is accompa nied by increased apolipoprotein E gene transcription. Using transfect ion analysis with 5' deletion mutations of the 5' control region of th e apo E gene in THP1 cells, we show that the -651 to +86 chloramphenic ol acetyltransferase (CAT) construct is efficiently expressed in the m onocyte; as has been reported for other cell types. Further, we found that an 176 bp region between -623 to -447 was required for the induct ion of apolipoprotein E gene transcription during 12-O-tetradecanoylph orbol-13-acetate-induced differentiation of monocytes to macrophages. Gel-retardation patterns of the apolipoprotein E promoter region using nuclear extracts from differentiated or undifferentiated THP1 cells r evealed altered binding of Ap1-like nuclear factor/s to the -620 to -5 83 bp region after macrophage differentiation. Mutation of an Ap1 elem ent at position -602 abolished specific binding of Ap1-like proteins t o the -620 to -583 bp fragment of the apo E gene and significantly red uced expression of a -623 to +86 apo E-CAT construct during differenti ation. These data indicate that differentiation-related expression of the apolipoprotein E gene following phorbol ester stimulation is trans duced by gene elements between -623 and -447. Furthermore, the data in dicate that transcriptional activation of the apo E gene during macrop hage differentiation is associated with induction of Ap1-like proteins which bind to the Ap1 response element present at -602 in the apolipo protein E gene and importantly contribute to enhanced gene expression.