Hypoxia inducible factor-1α regulates autophagy via the p27-E2F1 signaling pathway

Mol Med Rep. 2017 Aug;16(2):2107-2112. doi: 10.3892/mmr.2017.6794. Epub 2017 Jun 15.

Abstract

Autophagy is a highly conserved process by which the cell contents are delivered to lysosomes for degradation, or are used to provide macromolecules for energy generation under conditions of nutritional starvation. It has previously been demonstrated that cancer cells in hypoxic regions, with an oxygen concentration below the normal physiological level, express hypoxia inducible factor (HIF)‑1α, in order to adapt and survive. HIF‑1α is important in the regulation of oxygen homeostasis and the transcription of hundreds of genes in response to conditions of hypoxia, hence maintaining energy and redox homeostasis. To determine if HIF‑1α modulates autophagy and the underlying molecular mechanisms regulating this process, the human esophageal cancer EC109 and IMR90 human diploid fibroblast cell lines were exposed to normoxic or hypoxic conditions and the expression levels of various proteins subsequently examined. Small interfering RNA was used to silence p27, in order to investigate its role in the process of HIF‑1α regulated autophagy. Hypoxia induced autophagy in IMR90 cells and it was revealed that immature IMR90 cells demonstrated an increased rate of autophagy compared with mature cells. HIF‑1α promoted EC109 cell autophagy via positively modulating p27, whereas silencing of p27 abolished the autophagy induced by hypoxia. The present study identified the primary components of the p27‑E2F1 signaling pathway by which HIF‑1α regulates autophagy. A previously unidentified mechanism is here presented, via which cancer cells may generate energy, or obtain macromolecules for survival.

MeSH terms

  • Animals
  • Autophagy*
  • Carcinogenesis
  • Cell Hypoxia*
  • Cell Line
  • Cyclin-Dependent Kinase Inhibitor p27 / antagonists & inhibitors
  • Cyclin-Dependent Kinase Inhibitor p27 / genetics
  • Cyclin-Dependent Kinase Inhibitor p27 / metabolism*
  • E2F1 Transcription Factor / metabolism*
  • Humans
  • Hypoxia-Inducible Factor 1, alpha Subunit / metabolism*
  • Mice
  • Mice, Inbred NOD
  • Mice, SCID
  • Microtubule-Associated Proteins / metabolism
  • Neoplasms / pathology
  • RNA Interference
  • RNA, Small Interfering / metabolism
  • RNA-Binding Proteins / metabolism
  • Signal Transduction*
  • Transplantation, Heterologous

Substances

  • E2F1 Transcription Factor
  • E2F1 protein, human
  • Hypoxia-Inducible Factor 1, alpha Subunit
  • Microtubule-Associated Proteins
  • P62 protein, human
  • RNA, Small Interfering
  • RNA-Binding Proteins
  • Cyclin-Dependent Kinase Inhibitor p27