Transcriptional regulation of the mouse αA-crystallin gene: Activation dependent on a cyclic AMP-responsive element (DE1/CRE) and a Pax-6-binding site

Two cis-acting promoter elements (-108 to -100 and -49 to -33) of the mouse αA-crystallin gene, which is highly expressed in the ocular lens, were studied. Here we show that DE1 (-108 to -100; 5'TGACGGTG3'), which resembles the consensus cyclic AMP (cAMP)-responsive element sequence (CRE; 5'TGACGT[A/C][A/G]3'), behaves like a functional CRE site. Transfection experiments and electrophoretic mobility shift assays (EMSAs) using site- specific mutations correlated a loss of function with deviations from the CRE consensus sequence. Results of EMSAs in the presence of antisera against CREB, ΔCREB, and CREM were consistent with the binding of CREB-like proteins to the DE1 sequence. Stimulation of αA-crystallin promoter activity via 8- bromo-cAMP, forskolin, or human T-cell leukemia virus type I Tax₁ in transfections and reduction of activity of this site in cell-free transcription tests by competition with the somatostatin CRE supported the idea that DE1 is a functional CRE. Finally, Pax-6, a member of the paired- box family of transcription factors, activated the mouse αA-crystallin promoter in cotransfected COP-8 fibroblasts and bound to the -59 to -29 promoter sequence in EMSAs. These data provide evidence for a synergistic role of Pax-6 and CREB-like proteins for high expression of the mouse αA- crystallin gene in the lens.