Distinct functions of CCAAT enhancer-binding protein isoforms in the regulation of manganese superoxide dismutase during interleukin-1beta stimulation.
The mitochondrial antioxidant enzyme manganese superoxide dismutase (Mn-SOD) is crucial in maintaining cellular and organismal homeostasis. Mn-SOD expression is tightly regulated in a manner that synchronizes its cytoprotective functions during inflammatory challenges. Induction of Mn-SOD gene expression by the proinflammatory cytokine IL-1beta is mediated through a complex intronic enhancer element. To identify and characterize the transcription factors required for Mn-SOD enhancer function, a yeast one-hybrid assay was utilized, and two CCAAT enhancer-binding protein (C/EBP) members, C/EBP beta and C/EBP delta, were identified. These two transcription factors responded to IL-1beta treatment with distinct expression profiles, different temporal yet inducible interactions with the endogenous Mn-SOD enhancer, and also opposite effects on Mn-SOD transcription. C/EBP beta is expressed as three isoforms, LAP* (liver-activating protein), LAP, and LIP (liver-inhibitory protein). Our functional analysis demonstrated that only the full-length C/EBP beta/LAP* served as a true activator for Mn-SOD, whereas LAP, LIP, and C/EBP delta functioned as potential repressors. Finally, our systematic mutagenesis of the unique N-terminal 21 amino acids further solidified the importance of LAP* in the induction of Mn-SOD and emphasized the crucial role of this isoform. Our data demonstrating the physiological relevance of the N-terminal peptide also provide a rationale for revisiting the role of LAP* in the regulation of other genes and in pathways such as lipogenesis and development.
Qiu
Xiaolei
X
McKnight Brian Institute, University of Florida, Gainesville, Florida 32610, USA.
Aiken
Kimberly J
KJ
Chokas
Ann L
AL
Beachy
Dawn E
DE
Nick
Harry S
HS
D000818:Animals; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000378:metabolism; D051743:CCAAT-Enhancer-Binding Protein-delta / Q000378:metabolism; D022762:CCAAT-Enhancer-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D007249:Inflammation; D053583:Interleukin-1beta / Q000378:metabolism*; D008274:Magnesium / Q000737:chemistry; D008954:Models, Biological; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D051381:Rats; D013482:Superoxide Dismutase / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
D022763:CCAAT-Enhancer-Binding Protein-alpha; D022762:CCAAT-Enhancer-Binding Proteins; D053583:Interleukin-1beta; D020033:Protein Isoforms; D051743:CCAAT-Enhancer-Binding Protein-delta; D013482:Superoxide Dismutase; D008274:Magnesium