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Txr1: a transcriptional regulator of thrombospondin-1 that modulates cellular sensitivity to taxanes

¹ Department of Genetics, Stanford University School of Medicine, Stanford University, Stanford, California 94305, USA; ² Department of Medicine, Stanford University School of Medicine, Stanford University, Stanford, California 94305, USA

Using transcripts initiated at a chromosomally integrated retrovirus-based promoter to perturb gene expression randomly in human prostate cancer cells, we isolated cell clones resistant to taxane lethality and discovered the role of a previously uncharacterized gene, txr1, in this phenotype. We show that txr1 impedes taxane-induced apoptosis in tumor cells by transcriptionally down-regulating the production of thrombospondin-1 (TSP-1)—known earlier for both its anti-angiogenic and proapoptotic actions. Decrease of Txr1 or treatment with TSP-1 or TSP-1 mimetic peptide sensitized cells to taxane cytotoxicity by activating signaling through the CD47 receptor (also known as the integrin-associated protein), whereas interference with CD47 function reduced taxane-induced cell death. Cellular abundance of Txr1 and TSP-1 varied inversely, and alteration of the level of both proteins correlated highly with taxol resistance in 13 of 19 NCI-60 cancer cell lines. Our results reveal a hitherto unsuspected mechanism of taxane resistance, elucidate the role of txr1 in this resistance, and identify txr1 as a regulator of TSP-1 production and an agent for its chemotherapeutic modulation.

[Keywords: Thrombospondin-1; CD47; taxanes; microarray; angiogenesis; Txr1]

Received April 17, 2006; revised version accepted June 5, 2006.

E-MAIL sncohen{at}stanford.edu; FAX (650) 725-1536.

Supplemental material is available at http://www.genesdev.org.

Article published online ahead of print. Article and publication date are online at http://www.genesdev.org/cgi/doi/10.1101/gad.1441306

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