IκB kinase complex (IKK) triggers detachment-induced autophagy in mammary epithelial cells independently of the PI3K-AKT-MTORC1 pathway

Autophagy. 2013 Aug;9(8):1214-27. doi: 10.4161/auto.24870. Epub 2013 May 8.

Abstract

Adherent cells require proper integrin-mediated extracellular matrix (ECM) engagement for growth and survival; normal cells deprived of proper ECM contact undergo anoikis. At the same time, autophagy is induced as a survival pathway in both fibroblasts and epithelial cells upon ECM detachment. Here, we further define the intracellular signals that mediate detachment-induced autophagy and uncover an important role for the IκB kinase (IKK) complex in the induction of autophagy in mammary epithelial cells (MECs) deprived of ECM contact. Whereas the PI3K-AKT-MTORC1 pathway activation potently inhibits autophagy in ECM-detached fibroblasts, enforced activation of this pathway is not sufficient to suppress detachment-induced autophagy in MECs. Instead, inhibition of IKK, as well as its upstream regulator, MAP3K7/TAK1, significantly attenuates detachment-induced autophagy in MECs. Furthermore, function-blocking experiments corroborate that both IKK activation and autophagy induction result from decreased ITGA3-ITGB1 (α3β1 integrin) function. Finally, we demonstrate that pharmacological IKK inhibition enhances anoikis and accelerates luminal apoptosis during acinar morphogenesis in three-dimensional culture. Based on these results, we propose that the IKK complex functions as a key mediator of detachment-induced autophagy and anoikis resistance in epithelial cells.

Keywords: anoikis; autophagy; extracellular matrix; integrin; mammary epithelial cells.

Publication types

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

MeSH terms

  • Animals
  • Antibodies / pharmacology
  • Apoptosis / drug effects
  • Autophagy* / drug effects
  • Cell Adhesion / drug effects
  • Embryo, Mammalian / cytology
  • Enzyme Activation / drug effects
  • Epithelial Cells / cytology*
  • Epithelial Cells / drug effects
  • Epithelial Cells / enzymology
  • Extracellular Matrix / drug effects
  • Extracellular Matrix / metabolism
  • Fibroblasts / cytology
  • Fibroblasts / drug effects
  • Fibroblasts / enzymology
  • Humans
  • I-kappa B Kinase / antagonists & inhibitors
  • I-kappa B Kinase / metabolism*
  • Integrin alpha3 / metabolism
  • Integrin beta1 / metabolism
  • MAP Kinase Kinase Kinases / metabolism
  • Mammary Glands, Human / cytology*
  • Mechanistic Target of Rapamycin Complex 1
  • Mice
  • Multiprotein Complexes / metabolism*
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Proto-Oncogene Proteins c-akt / metabolism*
  • Signal Transduction / drug effects
  • Substrate Specificity / drug effects
  • TOR Serine-Threonine Kinases / metabolism*

Substances

  • Antibodies
  • Integrin alpha3
  • Integrin beta1
  • Multiprotein Complexes
  • Mechanistic Target of Rapamycin Complex 1
  • Proto-Oncogene Proteins c-akt
  • TOR Serine-Threonine Kinases
  • I-kappa B Kinase
  • MAP Kinase Kinase Kinases
  • MAP kinase kinase kinase 7