Expression of t-DARPP mediates trastuzumab resistance in breast cancer cells

Abbes Belkhiri, Altaf A. Dar, Dun Fa Peng, Mohammad H. Razvi, Cammie Rinehart, Carlos L. Arteaga, Wael El-Rifai

Research output: Contribution to journalArticlepeer-review

35 Scopus citations


Purpose: We have investigated the role of t-DARPP in trastuzumab resistance in ERBB2-amplified and overexpressed breast cancer cell lines. Experimental Design: We have used the HR-5 and HR-6 trastuzumab-resistant cells that were established from tumors that recurred in the presence of trastuzumab therapy following xenografts of BT-474 cells in nude mice. In addition, SKBR-3 cells, engineered for stable expression of t-DARPP, and HCC-1569 cells, which have constitutive expression of t-DARPP and are de novo resistant to trastuzumab, were used. Results: We reported ≥15-fold up-regulation of mRNA and protein levels of t-DARPP in HR-5 and HR-6 cells compared with their progenitor BT-474 trastuzumab-sensitive cells. The t-DARPP expression was not regulated by changes in its promoter DNA methylation levels. The SKBR-3 cells stably expressing t-DARPP developed resistance to trastuzumab compared with their parental cells and empty vector controls (P < 0.01). The trastuzumab-resistant cell lines showed a significant increase in pAKT (Ser473) and BCL2 protein levels. The small interfering RNA knockdown of t-DARPP in all trastuzumab-resistant cells led to a significant reduction in ERBB2, pAKT (Ser473), and BCL2 protein levels with a significant decrease in cell viability (P ≤ 0.001) and an increase in cleaved caspase-3 levels, indicating the progression of these cells toward apoptosis. The t-DARPP protein was associated with both heat shock protein 90 and ERBB2 forming a potential protein complex. This association may play a role in regulating ERBB2 protein in trastuzumab-resistant cells. Conclusion: We conclude that t-DARPP is a novel molecular target that can mediate the therapeutic resistance to trastuzumab in breast cancer cells.

Original languageEnglish (US)
Pages (from-to)4564-4571
Number of pages8
JournalClinical Cancer Research
Issue number14
StatePublished - Jul 15 2008

ASJC Scopus subject areas

  • Oncology
  • Cancer Research


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