Department of Pharmacology & Experimental Therapeutics and The Marlene and Stewart Greenebaum Cancer Center, University of Maryland School of Medicine, Baltimore, MD, USA.
Drug resistance remains a clinical challenge in cancer treatment due to poor understanding of underlying mechanisms. We have established several drug-resistant prostate cancer cell lines by long-term culture in medium containing chemotherapeutic drugs. These resistant lines displayed a significant increase in side population cells due to overexpression of drug efflux pumps including ABCG2/BCRP and MDR1/Pgp. To uncover potential mechanisms underlying drug resistance, we performed microarray analysis to identify differentially expressed genes in 2 drug-resistant lines. We observed that POU5F1/OCT4, a transcription factor key to regulating pluripotency in embryonic stem cells, was upregulated in drug-resistant lines and accompanied by transcriptional activation of a set of its known target genes. Upregulation of OCT4 in drug-resistant cells was validated by RT-PCR and sequencing of PCR products as well as confirmation by Western blot and specific shRNA knockdown. Analysis of the regulatory region of POU5F1/OCT4 revealed a reduction of methylation in drug-resistant cell lines. Furthermore, these drug-resistant cells exhibited a significant increase in tumorigenicity in vivo. Subcutaneous inoculation of as few as 10 drug-resistant cells could initiate tumor formation in SCID mice, whereas no detectable tumors were observed from the parental line under similar conditions, suggesting that these drug-resistant cells may be enriched for tumor-initiating cells. Knocking down OCT4 expression by specific shRNAs attenuated growth of drug-resistant cells. Our data suggest that OCT4 re-expression in cancer cells may play an important role in carcinogenesis and provide one possible mechanism by which cancer cells acquire/maintain a drug-resistant phenotype.
Written by:
Linn DE, Yang X, Sun F, Xie Y, Chen H, Jiang R, Chen H, Chumsri S, Burger AM, Qiu Y. Are you the author?
Reference: Genes Cancer. 2010 Sep;1(9):908-16.
doi: 10.1177/1947601910388271
PubMed Abstract
PMID: 21779471
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