Hypoxia-induced HIF1α activation regulates small extracellular vesicle release in human embryonic kidney cells

Abstract

Extracellular vesicles (EVs) are membrane enclosures released by eukaryotic cells that carry bioactive molecules and serve to modulate biological responses in recipient cells. Both increased EV release and altered EV composition are associated with the development and progression of many pathologies including cancer. Hypoxia, a feature of rapidly growing solid tumours, increases the release of EVs. However, the molecular mechanisms remain unknown. The hypoxia inducible factors (HIFs) are transcription factors that act as major regulators of the cellular adaptations to hypoxia. Here, we investigated the requirement of HIF pathway activation for EV release in Human Embryonic Kidney Cells (HEK293). Time course experiments showed that EV release increased concomitantly with sustained HIF1α and HIF2α activation following the onset of hypoxia. shRNA mediated knock-down of HIF1α but not HIF2α abrogated the effect of hypoxia on EV release, suggesting HIF1α is involved in this process. However, stabilization of HIF proteins in normoxic conditions through: (i) heterologous expression of oxygen insensitive HIF1α or HIF2α mutants in normoxic cells or (ii) chemical inhibition of the prolyl hydroxylase 2 (PHD2) repressor protein, did not increase EV release, suggesting HIF activation alone is not sufficient for this process. Our findings suggest HIF1α plays an important role in the regulation of EV release during hypoxia in HEK293 cells, however other hypoxia triggered mechanisms likely contribute as stabilization of HIF1α alone in normoxia is not sufficient for EV release.

Strategies to Convert Cells into Hyaline Cartilage: Magic Spells for Adult Stem Cells

“…Due to their unique biological roles, EVs coordinate complex processes, such as development, inflammation, tumorigenesis and even maintenance of a stem cell niche [ 201 ]. EVs release responses to external influences, such as cyclic hydrostatic pressure [ 202 ], oxidative stress [ 203 ] and hypoxia [ 204 ]. Types of EVs are distinguished for subclasses by their fundamental mechanisms of biogenesis, diversity of their composition and size [ 205 ] and selective cargo loading [ 206 , 207 ].…”

Exosome biogenesis: machinery, regulation, and therapeutic implications in cancer

“…Xi et al showed that exosomes secreted by these CAFs promoted migration and invasion of breast cancer cells [ 162 ]. Notably, hypoxia inducible factor 1 (HIF1) was proposed to contribute to exosome generation, but the underlying mechanism remains unclear [ 163 ].…”

Lipid Droplets Fuel Small Extracellular Vesicle Biogenesis

“…Hypoxia also triggers LD formation through HIF1a stabilization. However, despite its role in sEV biogenesis under hypoxic condition, the stabilization of HIF1a in normoxia was not sufficient to support its role in sEV production (47). Overall, while the link between autophagy and LDs has already been well established and characterized, little is known about how LDs could fuel sEV biogenesis.…”