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

Belkhiri A, Dar AA, Peng DF, Razvi MH, Rinehart C, Arteaga CL, El-Rifai W
Clin Cancer Res. 2008 14 (14): 4564-71

PMID: 18579663 · PMCID: PMC2842884 · DOI:10.1158/1078-0432.CCR-08-0121

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 > or =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 (Ser(473)) 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 (Ser(473)), and BCL2 protein levels with a significant decrease in cell viability (P < or = 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.

MeSH Terms (22)

Animals Antibodies, Monoclonal Antibodies, Monoclonal, Humanized Antineoplastic Agents Apoptosis Blotting, Western Breast Neoplasms Cell Line, Tumor Dopamine and cAMP-Regulated Phosphoprotein 32 Drug Resistance, Neoplasm Female Gene Expression Humans Immunoprecipitation In Situ Nick-End Labeling Mice Protein Isoforms Receptor, ErbB-2 Reverse Transcriptase Polymerase Chain Reaction RNA, Small Interfering Trastuzumab Xenograft Model Antitumor Assays

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