Dual functions of autophagy in the response of breast tumor cells to radiation: cytoprotective autophagy with radiation alone and cytotoxic autophagy in radiosensitization by vitamin D 3

Autophagy. 2012 May 1;8(5):739-53. doi: 10.4161/auto.19313. Epub 2012 Apr 13.


In MCF-7 breast tumor cells, ionizing radiation promoted autophagy that was cytoprotective; pharmacological or genetic interference with autophagy induced by radiation resulted in growth suppression and/or cell killing (primarily by apoptosis). The hormonally active form of vitamin D, 1,25D 3, also promoted autophagy in irradiated MCF-7 cells, sensitized the cells to radiation and suppressed the proliferative recovery that occurs after radiation alone. 1,25D 3 enhanced radiosensitivity and promoted autophagy in MCF-7 cells that overexpress Her-2/neu as well as in p53 mutant Hs578t breast tumor cells. In contrast, 1,25D 3 failed to alter radiosensitivity or promote autophagy in the BT474 breast tumor cell line with low-level expression of the vitamin D receptor. Enhancement of MCF-7 cell sensitivity to radiation by 1,25D 3 was not attenuated by a genetic block to autophagy due largely to the promotion of apoptosis via the collateral suppression of protective autophagy. However, MCF-7 cells were protected from the combination of 1,25D 3 with radiation using a concentration of chloroquine that produced minimal sensitization to radiation alone. The current studies are consistent with the premise that while autophagy mediates a cytoprotective function in irradiated breast tumor cells, promotion of autophagy can also confer radiosensitivity by vitamin D (1,25D 3). As both cytoprotective and cytotoxic autophagy can apparently be expressed in the same experimental system in response to radiation, this type of model could be utilized to distinguish biochemical, molecular and/or functional differences in these dual functions of autophagy.

Publication types

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

MeSH terms

  • Autophagy / drug effects
  • Autophagy / genetics
  • Autophagy / radiation effects*
  • Breast Neoplasms / genetics
  • Breast Neoplasms / pathology*
  • Calcitriol / analogs & derivatives
  • Calcitriol / pharmacology
  • Cell Line, Tumor
  • Cholecalciferol / pharmacology*
  • Cytoprotection / drug effects*
  • Cytoprotection / radiation effects*
  • Drug Screening Assays, Antitumor
  • Female
  • Gene Silencing / drug effects
  • Humans
  • Phagosomes / drug effects
  • Phagosomes / radiation effects
  • Phagosomes / ultrastructure
  • Radiation Tolerance / drug effects*
  • Radiation Tolerance / radiation effects
  • Radiation, Ionizing*
  • Receptor, ErbB-2 / metabolism
  • Transfection
  • Vacuoles / drug effects
  • Vacuoles / radiation effects
  • Vacuoles / ultrastructure


  • Cholecalciferol
  • ERBB2 protein, human
  • Receptor, ErbB-2
  • Calcitriol
  • seocalcitol