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J Biol Chem. 2015 Sep 11;290(37):22851-61. doi: 10.1074/jbc.M115.656710. Epub 2015 Jul 27.

Divergent roles of CAAX motif-signaled posttranslational modifications in the regulation and subcellular localization of Ral GTPases.

Author information

1
From the Departments of Pharmacology and.
2
the Division of Cardiocirculatory Signaling, Okazaki Institute for Integrative Bioscience (National Institute for Physiological Sciences), National Institutes of Natural Sciences, 5-1 Higashiyama, Myoudaiji-cho, Okazaki, Aichi 444-8787, Japan.
3
From the Departments of Pharmacology and Radiation Oncology, and Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599 and.
4
From the Departments of Pharmacology and Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599 and cjder@med.unc.edu.

Abstract

The Ras-like small GTPases RalA and RalB are well validated effectors of RAS oncogene-driven human cancer growth, and pharmacologic inhibitors of Ral function may provide an effective anti-Ras therapeutic strategy. Intriguingly, although RalA and RalB share strong overall amino acid sequence identity, exhibit essentially identical structural and biochemical properties, and can utilize the same downstream effectors, they also exhibit divergent and sometimes opposing roles in the tumorigenic and metastatic growth of different cancer types. These distinct biological functions have been attributed largely to sequence divergence in their carboxyl-terminal hypervariable regions. However, the role of posttranslational modifications signaled by the hypervariable region carboxyl-terminal tetrapeptide CAAX motif (C = cysteine, A = aliphatic amino acid, X = terminal residue) in Ral isoform-selective functions has not been addressed. We determined that these modifications have distinct roles and consequences. Both RalA and RalB require Ras converting CAAX endopeptidase 1 (RCE1) for association with the plasma membrane, albeit not with endomembranes, and loss of RCE1 caused mislocalization as well as sustained activation of both RalA and RalB. In contrast, isoprenylcysteine carboxylmethyltransferase (ICMT) deficiency disrupted plasma membrane localization only of RalB, whereas RalA depended on ICMT for efficient endosomal localization. Furthermore, the absence of ICMT increased stability of RalB but not RalA protein. Finally, palmitoylation was critical for subcellular localization of RalB but not RalA. In summary, we have identified striking isoform-specific consequences of distinct CAAX-signaled posttranslational modifications that contribute to the divergent subcellular localization and activity of RalA and RalB.

KEYWORDS:

ICMT; RCE1; Ras protein; intracellular trafficking; plasma membrane; protein isoprenylation; protein palmitoylation; proteolytic enzyme; signal transduction; small GTPase

PMID:
26216878
PMCID:
PMC4566255
DOI:
10.1074/jbc.M115.656710
[Indexed for MEDLINE]
Free PMC Article

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