Rasal2 inhibits autophagic-exosomes secretion via regulating Rab27a in triple-negative breast cancer progression.

BACKGROUND: Triple-negative breast cancer (TNBC) is a subtype with the worst prognosis and there is still a lack of effective treatment. Exosomes (Exos) secreted by cancer cells to tumor microenvironment play an important role in cancer progression. We have demonstrated that the function of Rasal2 in the modulation of breast cancer progression is exos-mediated, but the relationship between Rasal2 and exosome secretion remains elusive. METHODS: Rasal2 knock-out (KO) MDA-MB-231 cells were conducted by crispr-cas9 technique and Rab27a knock-down (KD) in Rasal2 KO MDA-MB-231 cells (KO + KD) were further established by siRNA-mate plus transfection Reagent. Control (CT)/KO MDA-MB-231 cells stably overexpressing GFP-LC3 were generated by using GFP-LC3 plamisd. Transmission electron microscope (TEM), nanoparticle tracking analysis (NTA) and western blot analysis (WB) were used to identify exos derived from TNBC. Confocal microscopy was used to observe the autophagic flux and the colocalization of autophagosomes and multivesicular bodies (MVBs). Co-immunoprecipitation analysis was performed to determine the interaction between Rasal2 and Rab27a. Immunohistochemical analysis were used to detect the expression levels of autophagy-related proteins in tumor tissues of xenograft mice inoculated with CT/KO/KO + KD MDA-MB-231 cells. RESULTS: In this paper, we found that Rasal2 KO disrupts autophagic flux and induces secretory autophagy to promote autophagic-exos secretion in TNBC. Moreover, Rasal2 inhibits the activity of Rab27a which regulates vesicles transport and fusion, and Rab27a mediates Rasal2 KO-induced autophagic-exos secretion. Additionally, Rab27a KD inhibits Rasal2 KO-induced secretory autophagy, thereby promoting TNBC progression both in vivo and in vitro. CONCLUSIONS: Collectively, these findings delineated the role of Rab27a in TNBC progression modulated by Rasal2 through autophagy-exos pathway and suggested that it is of great significance for the early diagnosis, targeted therapy and prognosis judgement of TNBC from the perspective of tumor microenvironment.