Secretion of pro‐angiogenic extracellular vesicles during hypoxia is dependent on the autophagy‐related protein GABARAPL1

Abstract

Tumour hypoxia is a hallmark of solid tumours and contributes to tumour progression, metastasis development and therapy resistance. In response to hypoxia, tumour cells secrete pro‐angiogenic factors to induce blood vessel formation and restore oxygen supply to hypoxic regions. Extracellular vesicles (EVs) are emerging as mediators of intercellular communication in the tumour microenvironment. Here we demonstrate that increased expression of the LC3/GABARAP protein family member GABARAPL1, is required for endosomal maturation, sorting of cargo to endosomes and the secretion of EVs. Silencing GABARAPL1 results in a block in the early endosomal pathway and impaired secretion of EVs with pro‐angiogenic properties. Tumour xenografts of doxycycline inducible GABARAPL1 knockdown cells display impaired vascularisation that results in decreased tumour growth, elevated tumour necrosis and increased therapy efficacy. Moreover, our data show that GABARAPL1 is expressed on the EV surface and targeting GABARAPL1 + EVs with GABARAPL1 targeting antibodies results in blockade of pro‐angiogenic effects in vitro. In summary, we reveal that GABARAPL1 is required for EV cargo loading and secretion. GABARAPL1 + EVs are detectable and targetable and are therefore interesting to pursue as a therapeutic target.

TBK1 and GABARAP family members suppress Coxsackievirus B infection by limiting viral production and promoting autophagic degradation of viral extracellular vesicles

“…We have shown that knocking down TBK1 enhances CVB release through EVs, and we hypothesized this is due to disruption in GABA1/2-mediated autophagic flux. Based on recent literature that shows that TBK1 directly activates GABARAPL2 through phosphorylation to control autophagosome shedding and that secretion of EVs is dependent on GABARAPL1 [ 24 , 40 ], we hypothesize that TBK1 activates GABARAPL1 and GABARAPL2 to coordinate viral degradation in the host cells by chauffeuring virus-laden autophagosomes to the lysosome to be degraded. Because GABARAPL1 and GABARAPL2 are also required for autophagosome closure, we further hypothesize that silencing GABA1/2 restricts CVB infection early on by limiting the completion of autophagosome structures used by CVB for replication [ 41 – 43 ].…”

Oxidative-Damaged Mitochondria Activate GABARAPL1-Induced NLRP3 Inflammasomes in an Autophagic-Exosome Manner after Acute Myocardial Ischemia

“…The study of Ikeda et al [ 38 ] showed that mitochondria-rich extracellular vesicles from autologous stem cell-derived cardiomyocytes restored the energetics of the ischemic myocardium. The study of Keulers et al [ 39 ] showed that GEC1 is required for EV cargo loading and secretion. Based on these findings, we hypothesized and confirmed that the oxidative-damaged mitochondria block GEC1-mediated autophagy flux and are released by exosomes in exfoliated cardiac CMECs and blood CECs after AMI.…”

Autophagy and autophagy-related pathways in cancer

“…LDELS also requires LC3-dependent activation of neutral sphingomyelinase (nSMase-2, also known as SMPD3), which has been proposed to mediate intraluminal budding at the multivesicular body during EV biogenesis 104 . Although the precise roles of LDELS in cancer still remain unknown, it is noteworthy that the ATG8 family protein GABARAPL1 facilitates both cargo loading and the biogenesis of pro-angiogenic EVs in hypoxic tumour cells 105 . In addition to LDELS, ATG8 family proteins have been implicated in the release of extracellular DNA and histones independently of EVs, although the genetic role of ATG proteins involved in such processes remains obscure 106 .…”