The emerging role of the RAB25 small GTPase in cancer

Abstract

RAB25, a member of the rat sarcoma (RAS) family of small GTPase, has been implicated in the pathophysiology of ovarian, breast and other cancers. Its role in endosomal transport and recycling of cell-surface receptors and signaling proteins presents a novel paradigm for the disruption of cellular pathways and promotion of tumor development and aggressiveness. Variations in structure and post-translational modifications control the localization of RAS superfamily proteins to specific subcellular compartments and recruitment of downstream effectors, allowing these small GTPases to function as sophisticated modulators of a complex and diverse range of cellular processes. Here, we review the link between RAB25 and tumor development and current knowledge regarding its possible roles in cancer.

Figure 1

Biological function of RAB11 family. RAB11 and Rab25, located in the ARE, PRE and TGN, are activated by molecular switches cycling between GDP-bound and GTP-bound states through interaction with the GDP dissociation inhibitor (GDI), guanine nucleotide exchange factor (GEF) and GTPase-activating proteins (GAPs). Once activated, RAB11 and RAB25 recruit specific downstream effectors for different biological functions.

Figure 2

Rab25 regulates EGF signaling. A) Immunofluorescence staining of EGFR (red) and Rab25 (green) in ovarian A2780 cells. Colocalization of EGFR and Rab25 (i.e. yellow) is indicated by arrows. Cells were cultured in complete media, then serum starved for 24 h (0 min), followed by addition of EGF to the final concentration of 100 ng/mL for indicated times. Single scale bar, 10 µm. B) Cell-surface EGFR level detection. Ovarian cancer A2780 cells stably expressing RAB25 or control cells were treated with 100 ng/mL EGF for different time-points. The EGFR level was measured by flow cytometry using a fluorescein isothiocyanate (FITC)-conjugated antibody specific to the extracellular EGFR. *p < 0.05. C) Rab25 expression alters EGFR-induced AKT activity. Ovarian cancer A2780 cells stably expressed Rab25 and control (pcDNA-transfected) cells, detected by western blotting analysis (upper panel), were stimulated with EGF 100 ng/mL for indicated times before total protein isolation and measured by reverse-phase protein lysate array (lower panel). *p < 0.01.

Figure 3

Rab25 Networks. A) Rab25 protein–protein interaction network. The network was constructed by querying the I2D database version 1.71 (http://ophid.utoronto.ca/i2d). Only direct, physical interactions were included, covering human curated, high-throughput, and interologous interactions (further details about interaction sources are present at http://ophid.utoronto.ca/ophidv2.201/statistics.jsp). The core network comprises 23 proteins (square-shape nodes) connected by 29 direct interactions (thick edges). Including interactions among the 23 core proteins results in the network with 1077 proteins and 1421 interactions, which are known (n = 1023), determined by high throughput (HTP) experiments (n = 246) or predicted interologs (n = 142). Individual interaction sources are listed at http://ophid.utoronto.ca/ophidv2.201/statistics.jsp. Importantly, known interactions connect 806 of the 1077 proteins. Node color corresponds to Gene Ontology biological function and edge color represents interaction source, according to legends. Network visualization was done in NAViGaTOR version 2.015 (http://ophid.utoronto.ca/navigator). B) Expression of Rab25 regulates TGF-β-induced promoter activity. P21cip, PAI and CAGA promoter luciferase constructs were transiently transfected in ovarian cancer A2780 stably expressing RAB25 or control (pcDNA) cells. TGF-β (1 µL: 100 ng/mL; 2 µL: 200 ng/mL) was added 24 h post-transfection. Luciferase activity was assayed 48 h post-transfection. *p < 0.01 versus control.