STRESS-INDUCED BINDING OF THE TRANSCRIPTION FACTOR CHOP TO A NOVEL DNA CONTROL ELEMENT

CHOP (GADD153) is a mammalian nuclear protein that dimerizes with memb ers of the C/EBP family of transcription factors, Absent under normal growth conditions, CHOP is induced by the stress encountered during nu trient deprivation, the acute-phase response, and treatment of cells w ith certain toxins, The basic region of CHOP deviates considerably in sequence from that of other C/EBP proteins, and CHOP-C/EBP heterodimer s are incapable of binding to a common class of C/EBP sites, With resp ect to such sites, CHOP serves as an inhibitor of the activity of C/EB P proteins, However, recent studies indicate that certain functions of CHOP, such as the induction of growth arrest by overexpression of the wild-type protein and on transformation by the TLS-CHOP fusion protei n, require an intact basic region, suggesting that DNA binding by CHOP may be implicated in these activities, In this study an in vitro PCR- based site selection assay was used to identify sequences bound by CHO P-C/EBP dimers, These sequences were found to contain a unique core el ement PuPuPuTGCAAT(A/C)CCC, Competition in DNA-binding assays, DNase I footprint analysis, and methylation interference demonstrate that the binding is sequence specific, Deletions in the basic region of CHOP l ead to a loss of DNA binding, suggesting that CHOP participates in thi s process, Stress induction in NIH 3T3 cells leads to the appearance o f CHOP-containing DNA-binding activity, CHOP is found to contain a tra nscriptional activation domain which is inducible by cellular stress, lending further support to the notion that the protein can function as a positively acting transcription factor, We conclude that CHOP may s erve a dual role both as an inhibitor of the ability of C/EBP proteins to activate some target genes and as a direct activator of others.