Ral GTPases promote metastasis by controlling biogenesis and organ colonization of exosomes

Abstract

<jats:p>Cancer extracellular vesicles (EVs) mainly exert pro-tumoral functions by changing the phenotypes of stromal cells to the benefit of tumor growth and metastasis. In particular, they shuttle to distant organs and seed pre-metastatic niches facilitating subsequent colonization by circulating tumor cells. The levels of tumor secreted EVs have been correlated with tumor aggressiveness, however, the link between EV secretion mechanisms and their capacity to form pre-metastatic niches remains obscure. Here, we show that GTPases of the Ral family control, through the phospholipase D1 (PLD1), multi-vesicular bodies homeostasis and thereby tune the biogenesis and secretion of pro-metastatic EVs. Mice experiments revealed that RalA and RalB promote lung metastasis of mammary carcinoma cells without affecting their invasive behaviors. Importantly, we demonstrate that EVs from RalA or RalB depleted cells have limited organotropic capacities in vivo and, as a consequence, are less efficient in seeding lung metastasis. Furthermore, we show that such EVs lack the adhesion molecule MCAM/CD146, which is responsible for EVs organotropism. Finally, we observe that RalA and RalB have increased expression in human breast cancer patients with lung metastasis. Altogether, our study identifies Ral GTPases as central molecules linking the mechanisms of EVs secretion, cargo loading to their capacity to disseminate and induce pre-metastatic niches.</jats:p>

The Small G-Protein RalA Promotes Progression and Metastasis of Triple Negative Breast Cancer

“…Our ndings are dissimilar from those reported in three recent studies where RALA and RALB were found to play similar roles in BC cell line models [20,21] or transient silencing of RALB was found to decrease BC cell line invasion [22]. In silico analyses utilizing the large TCGA and METABRIC breast cancer patient gene expression databases uncovered paradoxical associations between survival and RALA and RALB expression in support of our in vitro and in vivo ndings.…”

“…Additional studies will be needed determine if these disparate ndings are the result of cell line speci c effects or due to differences in study design. It has also been reported [20] [40]. Aurora A phosphorylates RALA on serine residues to alter subcellular localization and activity, and these target residues are not shared with RALB [41].…”

“…Recently, the C. elegans RAL homolog, RAL-1, was found to be required for the biogenesis and release of extracellular vesicles, important mediators of cell-cell communication [36]. This group has also shown that shRNA knockdown of either RALA or RALB in 4T1 mammary tumor cells leads to a signi cant reduction in secreted exosome-like vesicles and reduced lung metastatic capacity [20,36]. Our results suggest that RALA but not RALB contributes to metastatic outgrowth of BC, particularly TNBC, cell lines in the lungs.…”

The NANOTUMOR consortium – Towards the Tumor Cell Atlas

“…Identified alterations will guide us towards the molecular machineries/complexes that sustain higher order organelle alterations of cancer cells. Based on recently published work of the consortium (Ghoroghi et al., 2021), we have unanimously selected two GTPases of the Ral family (RalA and RalB) acting downstream of RAS, as proof of concept for the top‐down efforts of WP2. More generally, potent approaches such as localisation of organelle proteins by isotope tagging (Geladaki et al., 2019; Mulvey et al., 2017) as well as proximal interaction technologies using TurboID coupled to mass spectrometry will allow the identification of such complexes (Branon et al., 2018).…”

Tasmanian devil facial tumor-derived extracellular vesicles reveal mesenchymal transition markers and adhesion molecules related to metastasis

“…Several of the cell adhesion-related proteins highly enriched in DFTD EVs have been implicated in EVassociated metastasis, specifically in preparing the pre-metastatic niche in the lungs. In particular, the rasrelated proteins Ra1A and Ra1B, shown to promote lung metastasis in breast cancer (46) were upregulated in both DFT1 and DFT2 EVs relative to fibroblast EVs. We also found that the integrin subunit ITGA6, which can moderate tumor EV organotropism to the lung (20), was also significantly upregulated.…”