CHOP-Dependent Stress-Inducible Expression of a Novel Form of Carbonic Anhydrase VI

Abstract

CHOP (also called GADD153) is a stress-inducible nuclear protein that dimerizes with members of the C/EBP family of transcription factors and was initially identified as an inhibitor of C/EBP binding to classic C/EBP target genes. Subsequent experiments suggested a role for CHOP-C/EBP heterodimers in positively regulating gene expression; however, direct evidence that this is the case has so far not been uncovered. Here we describe the identification of a positively regulated direct CHOP-C/EBP target gene, that encoding murine carbonic anhydrase VI (CA-VI). The stress-inducible form of the gene is expressed from an internal promoter and encodes a novel intracellular form of what is normally a secreted protein. Stress-induced expression of CA-VI is both CHOP and C/EBPβ dependent in that it does not occur in cells deficient in either gene. A CHOP-responsive element was mapped to the inducible CA-VI promoter, and in vitro footprinting revealed binding of CHOP-C/EBP heterodimers to that site. Rescue of CA-VIexpression in c/ebpβ^−/− cells by exogenous C/EBPβ and a shorter, normally inhibitory isoform of the protein known as LIP suggests that the role of the C/EBP partner is limited to targeting the CHOP-containing heterodimer to the response element and points to a preeminent role for CHOP in CA-VI induction during stress.

ACKNOWLEDGMENTS

We are indebted to Valeria Poli for the gift of C/EBPβ knockout mice; to Ross Fernley and Thomas Maren for advice on carbonic anhydrases; to Tsonwin Hai for discussions on ATF3; to Edward Skolnik, Lennart Philipson, and members of their lab as well as the other members of the Ron lab for criticism and advice; and to Jue Yee Kim for assistance with the figure layouts.

This work was supported by NIH grants DK47119 and ES08681. J.S. is a trainee in the NYU MSTP program and supported by NIGMS grant GM07308. D.R. is a Stephen Birnbaum Scholar of the Leukemia Society of America.