High-throughput ectopic expression screen for tamoxifen resistance identifies an atypical kinase that blocks autophagy

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 108; no. 5; pp. 2058 - 2063
• Main Authors: Gonzalez-Malerva, Laura, Park, Jaehong, Zou, Lihua, Hu, Yanhui, Moradpour, Zahra, Pearlberg, Joseph, Sawyer, Jacqueline, Stevens, Hallam, Harlow, Ed, LaBaer, Joshua
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 01-02-2011; National Acad Sciences
• Subjects: Antineoplastic Agents, Hormonal - pharmacology; Apoptosis; Autophagy; Autophagy - drug effects; Biological Sciences; Breast cancer; Cell death; Cell growth; Cell Line, Tumor; Cell lines; Cohort Studies; Disease free survival; Drug resistance; Drug Resistance, Neoplasm; Estrogens; Gene expression; Gene Silencing; Genetic screening; Health outcomes; Heat-Shock Proteins - genetics; Heat-Shock Proteins - physiology; Human subjects; Humans; Kinases; Oligonucleotide Array Sequence Analysis; Oncology; Protein Kinases - metabolism; Protein-Serine-Threonine Kinases - genetics; Protein-Serine-Threonine Kinases - physiology; Signatures; Studies; Tamoxifen - pharmacology; Tumors
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1018157108

Resistance to tamoxifen in breast cancer patients is a serious therapeutic problem and major efforts are underway to understand underlying mechanisms. Resistance can be either intrinsic or acquired. We derived a series of subcloned MCF7 cell lines that were either highly sensitive or naturally resistant to tamoxifen and studied the factors that lead to drug resistance. Gene-expression studies revealed a signature of 67 genes that differentially respond to tamoxifen in sensitive vs. resistant subclones, which also predicts disease-free survival in tamoxifen-treated patients. High-throughput cell-based screens, in which >500 human kinases were independently ectopically expressed, identified 31 kinases that conferred drug resistance on sensitive cells. One of these, HSPB8, was also in the expression signature and, by itself, predicted poor clinical outcome in one cohort of patients. Further studies revealed that HSPB8 protected MCF7 cells from tamoxifen and blocked autophagy. Moreover, silencing HSBP8 induced autophagy and caused cell death. Tamoxifen itself induced autophagy in sensitive cells but not in resistant ones, and tamoxifen-resistant cells were sensitive to the induction of autophagy by other drugs. These results may point to an important role for autophagy in the sensitivity to tamoxifen.