Identification of a truncated β1-chimaerin variant that inactivates nuclear Rac1
- 22 December 2019
- journal article
- research article
- Published by Elsevier BV in Journal of Biological Chemistry
- Vol. 295 (5), 1300-1314
- https://doi.org/10.1074/jbc.ra119.008688
Abstract
β1-chimaerin belongs to the chimaerin family of GTPase-activating proteins (GAPs) and is encoded by the CHN2 gene that also encodes the β2- and β3-chimaerin isoforms. All chimaerin isoforms have a C1 domain that binds diacylglycerol (DAG), as well as the tumor-promoting phorbol esters, and a catalytic GAP domain that inactivates the small GTPase Rac. Nuclear Rac has emerged as a key regulator of various cell functions including cell division, and has a pathological role by promoting tumorigenesis and metastasis. However, how nuclear Rac is regulated has not been fully addressed. Here, using several approaches, including siRNA-mediated gene silencing, confocal microscopy, and subcellular fractionation we identified a nuclear variant of β1-chimaerin, β1-Δ7p-chimaerin, that participates in the regulation of nuclear Rac1. We show that β1-Δ7p-chimaerin is a truncated variant generated by alternative splicing at a cryptic splice site in exon 7. We found that, unlike other chimaerin isoforms, β1-Δ7p-chimaerin lacks a functional C1 domain and is not regulated by DAG. We found that β1-Δ7p-chimaerin localizes to the nucleus via a nuclear localization signal (NLS) in its N-terminus. We also identified a key nuclear export signal (NES) in β1-chimaerin that is absent in β1-Δ7p-chimaerin, causing the nuclear retention of this truncated variant. Functionally analyses revealed that β1-Δ7p-chimaerin inactivates nuclear Rac and negatively regulates the cell cycle. Our results provide important insights into the diversity of chimaerin Rac-GAP regulation and function, and highlight a potential mechanism of nuclear Rac inactivation that may play significant roles in pathologies such as cancer.Keywords
Funding Information
- Consejería de Educación, Junta de Castilla y León (CSI242P18)
- National Institutes of Health (R01-ES026023, R01-CA189765, R01-CA196232)
This publication has 70 references indexed in Scilit:
- The RacGAP β2-Chimaerin Selectively Mediates Axonal Pruning in the HippocampusCell, 2012
- p65 Negatively Regulates Transcription of the Cyclin E GenePublished by Elsevier BV ,2010
- Systematic identification of cell cycle-dependent yeast nucleocytoplasmic shuttling proteins by prediction of composite motifsProceedings of the National Academy of Sciences of the United States of America, 2009
- β2‐Chimaerin binds to EphA receptors and regulates cell migrationFEBS Letters, 2009
- Mechanistic Analysis of the Amplification and Diversification Events Induced by Vav Proteins in B-lymphocytesJournal of Biological Chemistry, 2008
- Role of chimaerins, a group of Rac-specific GTPase activating proteins, in T-cell receptor signalingCellular Signalling, 2008
- GEFs and GAPs: Critical Elements in the Control of Small G ProteinsCell, 2007
- Phospholipase Cγ/diacylglycerol-dependent activation of β2-chimaerin restricts EGF-induced Rac signalingThe EMBO Journal, 2006
- Structural Mechanism for Lipid Activation of the Rac-Specific GAP, β2-ChimaerinCell, 2004
- Crystal structure of the Cys2 activator-binding domain of protein kinase Cδ in complex with phorbol esterCell, 1995