Everolimus induces G1 cell cycle arrest through autophagy-mediated protein degradation of cyclin D1 in breast cancer cells

Am J Physiol Cell Physiol. 2019 Aug 1;317(2):C244-C252. doi: 10.1152/ajpcell.00390.2018. Epub 2019 May 22.


Everolimus inhibits mammalian target of rapamycin complex 1 (mTORC1) and is known to cause induction of autophagy and G1 cell cycle arrest. However, it remains unknown whether everolimus-induced autophagy plays a critical role in its regulation of the cell cycle. We, for the first time, suggested that everolimus could stimulate autophagy-mediated cyclin D1 degradation in breast cancer cells. Everolimus-induced cyclin D1 degradation through the autophagy pathway was investigated in MCF-10DCIS.COM and MCF-7 cell lines upon autophagy inhibitor treatment using Western blot assay. Everolimus-stimulated autophagy and decrease in cyclin D1 were also tested in explant human breast tissue. Inhibiting mTORC1 with everolimus rapidly increased cyclin D1 degradation, whereas 3-methyladenine, chloroquine, and bafilomycin A1, the classic autophagy inhibitors, could attenuate everolimus-induced cyclin D1 degradation. Similarly, knockdown of autophagy-related 7 (Atg-7) also repressed everolimus-triggered cyclin D1 degradation. In addition, everolimus-induced autophagy occurred earlier than everolimus-induced G1 arrest, and blockade of autophagy attenuated everolimus-induced G1 arrest. We also found that everolimus stimulated autophagy and decreased cyclin D1 levels in explant human breast tissue. These data support the conclusion that the autophagy induced by everolimus in human mammary epithelial cells appears to cause cyclin D1 degradation resulting in G1 cell cycle arrest. Our findings contribute to our knowledge of the interplay between autophagy and cell cycle regulation mediated by mTORC1 signaling and cyclin D1 regulation.

Keywords: autophagy; cell cycle; cyclin D1; everolimus; mTORC1 inhibitor.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • Autophagy / drug effects*
  • Autophagy-Related Protein 7 / genetics
  • Autophagy-Related Protein 7 / metabolism
  • Breast Neoplasms / drug therapy*
  • Breast Neoplasms / genetics
  • Breast Neoplasms / metabolism
  • Breast Neoplasms / pathology
  • Cell Proliferation / drug effects*
  • Cyclin D1 / genetics
  • Cyclin D1 / metabolism*
  • Everolimus / pharmacology*
  • Female
  • G1 Phase Cell Cycle Checkpoints / drug effects*
  • Humans
  • MCF-7 Cells
  • Mechanistic Target of Rapamycin Complex 1 / antagonists & inhibitors
  • Mechanistic Target of Rapamycin Complex 1 / metabolism
  • Protein Kinase Inhibitors / pharmacology*
  • Proteolysis
  • Signal Transduction
  • Tissue Culture Techniques


  • Antineoplastic Agents
  • CCND1 protein, human
  • Protein Kinase Inhibitors
  • Cyclin D1
  • Everolimus
  • Mechanistic Target of Rapamycin Complex 1
  • ATG7 protein, human
  • Autophagy-Related Protein 7