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Calmodulin controls liver proliferation via interactions with C/EBPbeta-LAP and C/EBPbeta-LIP
Daniel Orellana1, Xiaoying Liu, Gou-Li Wang
1Huffington Center on Aging and Department of Pathology and Immunology, Baylor College of Medicine, Houston, Texas 77030, USA.
The Journal of Biological Chemistry
|May 26, 2010
Summary
Calmodulin (CaM) inhibits liver proliferation by interacting with C/EBPbeta-LIP, a protein driving liver growth. This calcium-CaM signaling pathway regulates liver cell activity, supporting quiescence.
Area of Science:
- Hepatology
- Molecular Biology
- Cell Signaling
Background:
- The truncated C/EBPbeta-LIP isoform promotes liver proliferation and is elevated in tumors and during the acute phase response (APR).
- Mechanisms regulating C/EBPbeta-LIP activity in the liver, particularly during APR, are not fully understood.
Purpose of the Study:
- To elucidate the molecular mechanisms by which liver proliferation is regulated by C/EBPbeta-LIP.
- To investigate the role of calmodulin (CaM) and calcium signaling in controlling C/EBPbeta-LIP activity.
Main Methods:
- Investigated interactions between C/EBPbeta-LIP and calmodulin (CaM) in liver cells.
- Utilized mutant CaM and mouse models (LPS-treated) to assess the impact on liver proliferation.
- Examined the effect of C/EBPbeta-LIP on E2F-Rb complexes and cell cycle gene regulation.
Main Results:
- Calmodulin directly inhibits C/EBPbeta-LIP-driven liver proliferation during APR via Ca(2+)-dependent interactions.
- Reduced nuclear Ca(2+) during APR impairs CaM's inhibitory function, while increased Ca(2+) in proliferating livers enhances it.
- CaM down-regulation or C/EBPbeta-LIP overexpression in LPS-treated mice induces liver proliferation.
- C/EBPbeta-LIP disrupts E2F-Rb complexes to promote cell cycle gene expression, an effect inhibited by CaM.
Conclusions:
- Calcium-CaM signaling represents a novel regulatory pathway for liver proliferation by modulating C/EBPbeta-LIP activity.
- CaM's regulation of both C/EBPbeta-LIP and C/EBPbeta-LAP isoforms suggests a broad role in liver biology.
- This pathway offers potential therapeutic targets for liver diseases characterized by aberrant proliferation.
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