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CHOP-Dependent stress-inducible expression of a novel form of carbonic anhydrase VI
J Sok1, X Z Wang, N Batchvarova
1Skirball Institute of Biomolecular Medicine, Departments of Medicine and Cell Biology, and Kaplan Cancer Center, New York University Medical Center, New York, New York 10016, USA.
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/EBPbeta 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-VI expression in c/ebpbeta-/- cells by exogenous C/EBPbeta 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.
Insights
The study identifies carbonic anhydrase VI (CA-VI) as a direct target gene regulated by the stress-inducible protein CHOP (GADD153) and C/EBP transcription factors. This reveals a novel role for CHOP in positively controlling gene expression during cellular stress.
Area of Science:
- Molecular Biology
- Gene Regulation
- Cellular Stress Response
Background:
- CHOP (GADD153) is a stress-inducible protein known to dimerize with C/EBP transcription factors.
- CHOP was initially thought to inhibit C/EBP binding, but later studies suggested a positive regulatory role, lacking direct evidence.
- The function of CHOP-C/EBP heterodimers in gene regulation remained unclear.
Purpose of the Study:
- To identify a direct target gene positively regulated by CHOP-C/EBP heterodimers.
- To investigate the role of CHOP and C/EBPbeta in the stress-induced expression of a novel gene.
- To elucidate the mechanism of CHOP-mediated gene activation.
Main Methods:
- Identification and characterization of the murine carbonic anhydrase VI (CA-VI) gene as a direct target.
- Analysis of stress-induced CA-VI expression in cells deficient in CHOP or C/EBPbeta.
- Mapping of a CHOP-responsive element in the CA-VI promoter and in vitro footprinting assays.
- Rescue experiments using C/EBPbeta and its isoform LIP.
Main Results:
- Murine carbonic anhydrase VI (CA-VI) was identified as a novel, positively regulated, direct target gene of CHOP-C/EBP heterodimers.
- Stress-induced CA-VI expression is dependent on both CHOP and C/EBPbeta.
- A specific CHOP-responsive element was found in the CA-VI promoter, with evidence of CHOP-C/EBP heterodimer binding.
- C/EBPbeta's role appears to be targeting CHOP to the response element, highlighting CHOP's primary role in induction.
Conclusions:
- CHOP plays a crucial role in the positive regulation of the CA-VI gene during cellular stress.
- The study provides direct evidence for CHOP-C/EBP heterodimers positively regulating gene expression.
- A novel intracellular form of CA-VI is produced under stress conditions, regulated by CHOP.