AUTOREGULATION OF THE HUMAN C EBP-ALPHA GENE BY STIMULATION OF UPSTREAM STIMULATORY FACTOR-BINDING/

The human C/EBP alpha gene promoter shares significant sequence homolo gy with that of the mouse but has a different mechanism of autoregulat ion, Activation of the murine promoter by direct binding of C/EBP alph a to a site within 200 bp of the transcriptional start was shown to el evate activity by approximately threefold (R. J. Christy, K. H. Kaestn er, D. E. Geiman, and M. D. Lane, Proc. Natl. Acad. Sci. USA 88:2593-2 597, 1991; K. Legraverend, P. Antonson, P. Flodby, and K. G. Xanthapou los, Nucleic Acids Res. 21:1735-1742, 1993). Unlike its murine counter part, the human C/EBP alpha gene promoter does not contain a cis eleme nt that binds the C/EBP alpha protein. Neither C/EBP alpha nor C/EBP b eta (NF-II-6) binds the human C/EBP alpha promoter within 437 bp. Howe ver, cotransfection studies show that C/EBP alpha stimulates transcrip tion of a reporter gene driven by 437 bp of the C/EBP alpha promoter, Our studies show that the human C/EBP alpha protein stimulates USF to bind to a USF consensus element within C/EBP alpha promoter and activa tes it by two- to threefold, We propose that the human gene employs th e ubiquitously expressed DNA-binding protein factor USF to carry out a utoregulation, Autoregulation of the human C/EBP alpha promoter was ab olished by deletion of the USF binding site, CACGTG. Expression of hum an C/EBP beta following transfection did not stimulate USF binding, Th ese studies suggest a mechanism whereby tissue-specific autoregulation can be achieved via a trans-acting factor that is expressed in all ce ll types. Thus, direct binding of the C/EBP alpha protein to the promo ter of the C/EBP alpha gene is not required for autoregulation.