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PMID: 10022857 Published · ppublish English Journal Article Research Support, U.S. Gov't, P.H.S.

C/EBPalpha regulates generation of C/EBPbeta isoforms through activation of specific proteolytic cleavage.

Molecular and cellular biology ·Vol. 19 ·No. 3 ·1999-03-00 ·Pages 1695-704

Welm AL, Timchenko NA, Darlington GJ

Abstract

C/EBPalpha and C/EBPbeta are intronless genes that can produce several N-terminally truncated isoforms through the process of alternative translation initiation at downstream AUG codons. C/EBPbeta has been reported to produce four isoforms: full-length 38-kDa C/EBPbeta, 35-kDa LAP (liver-enriched transcriptional activator protein), 21-kDa LIP (liver-enriched transcriptional inhibitory protein), and a 14-kDa isoform. In this report, we investigated the mechanisms by which C/EBPbeta isoforms are generated in the liver and in cultured cells. Using an in vitro translation system, we found that LIP can be generated by two mechanisms: alternative translation and a novel mechanism-specific proteolytic cleavage of full-length C/EBPbeta. Studies of mice in which the C/EBPalpha gene had been deleted (C/EBPalpha-/-) showed that the regulation of C/EBPbeta proteolysis is dependent on C/EBPalpha. The induction of C/EBPalpha in cultured cells leads to induced cleavage of C/EBPbeta to generate the LIP isoform. We characterized the cleavage activity in mouse liver extracts and found that the proteolytic cleavage activity is specific to prenatal and newborn livers, is sensitive to chymostatin, and is completely abolished in C/EBPalpha-/- animals. The lack of cleavage activity in the livers of C/EBPalpha-/- mice correlates with the decreased levels of LIP in the livers of these animals. Analysis of LIP production during liver regeneration showed that, in this system, the transient induction of LIP is dependent on the third AUG codon and most likely involves translational control. We propose that there are two mechanisms by which C/EBPbeta isoforms might be generated in the liver and in cultured cells: one that is determined by translation and a second that involves C/EBPalpha-dependent, specific proteolytic cleavage of full-length C/EBPbeta. The latter mechanism implicates C/EBPalpha in the regulation of posttranslational generation of the dominant negative C/EBPbeta isoform, LIP.

MeSH Terms
Animals Animals, Newborn CCAAT-Enhancer-Binding Protein-beta CCAAT-Enhancer-Binding Proteins Cell Line Cell-Free System Cysteine Endopeptidases/metabolism Cysteine Proteinase Inhibitors/pharmacology DNA/metabolism DNA-Binding Proteins/genetics,metabolism Dimerization Enzyme Activation Liver/metabolism,physiology Liver Regeneration Mice Mice, Knockout Nuclear Proteins/genetics,metabolism Oligopeptides/pharmacology Protein Biosynthesis Protein Isoforms Repressor Proteins/biosynthesis Serine Proteinase Inhibitors/pharmacology Tissue Extracts
Chemicals
CCAAT-Enhancer-Binding Protein-beta CCAAT-Enhancer-Binding Proteins Cysteine Proteinase Inhibitors DNA-Binding Proteins Nuclear Proteins Oligopeptides Protein Isoforms Repressor Proteins Serine Proteinase Inhibitors Tissue Extracts DNA chymostatin Cysteine Endopeptidases
Authors & Affiliations
3 authors, click to expand affiliations / ORCID
Welm A L
Department of Pathology, Baylor College of Medicine, Houston, Texas 77030, USA.
Timchenko N A
Darlington G J
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Article Info
Journal
Molecular and cellular biology
Abbr.
Mol Cell Biol
ISSN
0270-7306
DOI
10.1128/MCB.19.3.1695
Published
1999-03-00
Pages
1695-704
Language
English
Region
United States
NLM ID
8109087
PMCID
PMC83963
Subset
IM
Grants
NIDDK NIH HHS · R01 DK053045 · United States
NIGMS NIH HHS · R01 GM055188 · United States
NIDDK NIH HHS · R01-DK53045 · United States
Intramural NIH HHS · Z01 AG000766 · United States
NIGMS NIH HHS · GM55188 · United States
External Links
PubMed source DOI: 10.1128/MCB.19.3.1695 PMC Full Text View journal details
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