Indole-3-carbinol and its N-alkoxy derivatives preferentially target ERα-positive breast cancer cells

Cell Cycle. 2014;13(16):2587-99. doi: 10.4161/15384101.2015.942210.

Abstract

Indole-3-carbinol (I3C) is a natural anti-carcinogenic compound found at high concentrations in Brassica vegetables. I3C was recently reported to inhibit neutrophil elastase (NE) activity, while consequently limiting the proteolytic processing of full length cyclin E into pro-tumorigenic low molecular weight cyclin E (LMW-E). In this study, we hypothesized that inhibition of NE activity and resultant LMW-E generation is critical to the anti-tumor effects of I3C. LMW-E was predominately expressed by ERα-negative breast cancer cell lines. However, ERα-positive cell lines demonstrated the greatest sensitivity to the anti-tumor effects of I3C and its more potent N-alkoxy derivatives. We found that I3C was incapable of inhibiting NE activity or the generation of LMW-E. Therefore, this pathway did not contribute to the anti-tumor activity of I3C. Gene expression analyzes identified ligand-activated aryl hydrocarbon receptor (AhR), which mediated sensitivity to the anti-tumor effects of I3C in ERα-positive MCF-7 cells. In this model system, the reactive oxygen species (ROS)-induced upregulation of ATF-3 and pro-apoptotic BH3-only proteins (e.g. NOXA) contributed to the sensitivity of ERα-positive breast cancer cells to the anti-tumor effects of I3C. Overexpression of ERα in MDA-MB-231 cells, which normally lack ERα expression, increased sensitivity to the anti-tumor effects of I3C, demonstrating a direct role for ERα in mediating the sensitivity of breast cancer cell lines to I3C. Our results suggest that ERα signaling amplified the pro-apoptotic effect of I3C-induced AhR signaling in luminal breast cancer cell lines, which was mediated in part through oxidative stress induced upregulation of ATF-3 and downstream BH3-only proteins.

Keywords: AhR, aryl hydrocarbon receptor; CYP, cytochrome p450 oxidases; DIM, 3,3-diindoylmethane; ERα, estrogen receptor α; HMECs, human mammary epithelial cells; I3C, indole-3-carbinol; LMW-E, low molecular weight cyclin E; NE, neutrophil elastase; ROS, reactive oxygen species; RPPA, reverse phase protein array; TNBC, triple-receptor negative breast cancer; aryl hydrocarbon receptor; estrogen receptor α; indole-3-carbinol; neutrophil elastase.

MeSH terms

  • Alcohols / chemistry
  • Alcohols / pharmacology*
  • Antineoplastic Agents / chemistry
  • Antineoplastic Agents / pharmacology*
  • Apoptosis / drug effects
  • Breast Neoplasms / metabolism*
  • Breast Neoplasms / pathology
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Cyclin E / metabolism
  • Estrogen Receptor alpha / metabolism*
  • Female
  • Gene Expression Regulation, Neoplastic / drug effects
  • Humans
  • Indoles / chemistry
  • Indoles / pharmacology*
  • Leukocyte Elastase / metabolism
  • Metabolic Networks and Pathways / drug effects*
  • Receptors, Aryl Hydrocarbon / metabolism
  • Signal Transduction / drug effects

Substances

  • Alcohols
  • Antineoplastic Agents
  • Cyclin E
  • Estrogen Receptor alpha
  • Indoles
  • Receptors, Aryl Hydrocarbon
  • alkoxyl radical
  • estrogen receptor alpha, human
  • indole-3-carbinol
  • Leukocyte Elastase