Upregulation of PKC-delta contributes to antiestrogen resistance in mammary tumor cells

Oncogene. 2005 Apr 28;24(19):3166-76. doi: 10.1038/sj.onc.1208502.


Acquired resistance to tamoxifen (Tam) in breast cancer patients is a serious therapeutic problem. We have previously reported that protein kinase C-delta (PKC-delta) plays a major role in estrogen (E2)-mediated cell proliferation. To determine if PKC-delta is one of the major alternate signaling pathways that supports cell growth in the presence of Tam, we determined the levels of PKC isoforms in four different models of antiestrogen-resistant cells. Three out of four antiestrogen resistance cell lines (Tam/MCF-7, ICI/MCF-7 and HER-2/MCF-7) expressed significantly high levels of both total and activated PKC-delta levels compared to sensitive cells. Estrogen receptor (ER) alpha content and function are maintained in all the antiestrogen-resistant cell lines. Overexpressing active PKC-delta in Tam-sensitive MCF-7 cells (PKC-delta/MCF-7) led to Tam resistance both in vitro and in vivo. Inhibition of PKC-delta by rottlerin (a relatively specific inhibitor of PKC-delta) or siRNA significantly inhibited estrogen- and Tam-induced growth in antiestrogen-resistant cells. PKC-delta levels are significantly higher in Tam-resistant tumors compared to Tam-sensitive tumors in xenograft model (P<0.05). Taken together, these data suggest that PKC-delta plays a major role in antiestrogen resistance in breast tumor cells and thus provides a new target for treatment.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acetophenones / pharmacology
  • Animals
  • Benzopyrans / pharmacology
  • Blotting, Western
  • Cell Line, Tumor
  • Cell Proliferation
  • DNA / metabolism
  • Drug Resistance, Neoplasm*
  • Estrogen Receptor Modulators / pharmacology*
  • Female
  • Gene Expression Regulation, Neoplastic*
  • Humans
  • MAP Kinase Signaling System
  • Mammary Neoplasms, Animal / metabolism*
  • Mice
  • Mice, Nude
  • Microscopy, Confocal
  • Microscopy, Fluorescence
  • Neoplasm Transplantation
  • Phosphorylation
  • Protein Isoforms
  • Protein Kinase C / biosynthesis*
  • Protein Kinase C-delta
  • RNA Interference
  • RNA, Small Interfering / metabolism
  • Signal Transduction
  • Time Factors
  • Transfection
  • Up-Regulation*


  • Acetophenones
  • Benzopyrans
  • Estrogen Receptor Modulators
  • Protein Isoforms
  • RNA, Small Interfering
  • DNA
  • rottlerin
  • Prkcd protein, mouse
  • PRKCD protein, human
  • Protein Kinase C
  • Protein Kinase C-delta