Exosome-dependent immune surveillance at the metastatic niche requires BAG6 and CBP/p300-dependent acetylation of p53

Abstract

Extracellular vesicles released by tumor cells contribute to the reprogramming of the tumor microenvironment and interfere with hallmarks of cancer including metastasis. Notably, melanoma cell-derived EVs are able to establish a pre-metastatic niche in distant organs, or on the contrary, exert anti-tumor activity. However, molecular insights into how vesicles are selectively packaged with cargo defining their specific functions remain elusive.Methods: Here, we investigated the role of the chaperone Bcl2-associated anthogene 6 (BAG6, synonym Bat3) for the formation of pro- and anti-tumor EVs. EVs collected from wildtype cells and BAG6-deficient cells were characterized by mass spectrometry and RNAseq. Their tumorigenic potential was analyzed using the B-16V transplantation mouse melanoma model.Results: We demonstrate that EVs from B-16V cells inhibit lung metastasis associated with the mobilization of Ly6Clow patrolling monocytes. The formation of these anti-tumor-EVs was dependent on acetylation of p53 by the BAG6/CBP/p300-acetylase complex, followed by recruitment of components of the endosomal sorting complexes required for transport (ESCRT) via a P(S/T)AP double motif of BAG6. Genetic ablation of BAG6 and disruption of this pathway led to the release of a distinct EV subtype, which failed to suppress metastasis but recruited tumor-promoting neutrophils to the pre-metastatic niche.Conclusion: We conclude that the BAG6/CBP/p300-p53 axis is a key pathway directing EV cargo loading and thus a potential novel microenvironmental therapeutic target.

Regulation of exosome production and cargo sorting

“…The ability of Nedd4 family recognizes the late (L) domaincontaining proteins through the WW domain and the PY motif and sorts into exosomes [96][97][98]. The BAG6 plays a regulatory role on exosome cargoes loading via association with components of the ESCRT complex [99]. As described, the motif P(S/T)AP of BAG6 to be crucial for the direct association with Tsg101, an interaction mechanism reminiscent to the ESCRT recruitment during virus assembly [99].…”

Exosomes in Immune Regulation

“…This mechanism required the activation of the transcription factor Nr4a1 and was dependent on pigment epithelium-derived factor [PEDF] on the outer surface of ExVs. Likewise, Schuldner et al [ 147 ] also investigated the inhibitory effect of melanoma-derived ExVs on lung metastasis mediated by the mobilization of Ly6C low . In this case, the formation of anti-tumor-ExVs was dependent on acetylation of p53 to elicit an immune response.…”

p53’s Extended Reach: The Mutant p53 Secretome

“…For instance, wild-type p53 enhances exosome production in response to DNA-damage via transcriptional upregulation of TSAP-6 and CHMP4C [185,186]. In addition, p53 alters the exosomal content and size in colorectal carcinoma cells via HGS, a key component of the endosomal sorting complex [187]. Intriguingly, loading of EVs with anti-metastatic cargo, such as metalloproteinase inhibitor TIMP-3, was shown to be dependent on p53 acetylation by the BAG6/CBP/p300 complex followed by recruitment of the ESCRT (endosomal sorting complex required for transport) machinery [187].…”