ROCK inhibition promotes microtentacles that enhance reattachment of breast cancer cells
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Lekhana Bhandary1,2, Rebecca A. Whipple1, Michele I. Vitolo1,2,3, Monica S. Charpentier1, Amanda E. Boggs1, Kristi R. Chakrabarti1,2, Keyata N. Thompson1 and Stuart S. Martin1,2,3
1 University of Maryland School of Medicine, Marlene and Stewart Greenebaum National Cancer Institute Cancer Center, University of Maryland, School of Medicine, Baltimore, Maryland, USA
2 Graduate Program in Molecular Medicine, University of Maryland, School of Medicine, Baltimore, Maryland, USA
3 Department of Physiology, University of Maryland, School of Medicine, Baltimore, Maryland, USA
Stuart S. Martin, email:
Keywords: ROCK, microtentacles, Y-27632, breast cancer metastasis, reattachment
Received: November 24, 2014 Accepted: January 12, 2015 Published: January 31, 2015
The presence of circulating tumor cells (CTCs) in blood predicts poor patient outcome and CTC frequency is correlated with higher risk of metastasis. Recently discovered, novel microtubule-based structures, microtentacles, can enhance reattachment of CTCs to the vasculature. Microtentacles are highly dynamic membrane protrusions formed in detached cells and occur when physical forces generated by the outwardly expanding microtubules overcome the contractile force of the actin cortex. Rho-associated kinase (ROCK) is a major regulator of actomyosin contractility and Rho/ROCK over-activation is implicated in tumor metastasis. ROCK inhibitors are gaining popularity as potential cancer therapeutics based on their success in reducing adherent tumor cell migration and invasion. However, the effect of ROCK inhibition on detached cells in circulation is largely unknown. In this study, we use breast tumor cells in suspension to mimic detached CTCs and show that destabilizing the actin cortex through ROCK inhibition in suspended cells promotes the formation of microtentacles and enhances reattachment of cells from suspension. Conversely, increasing actomyosin contraction by Rho over-activation reduces microtentacle frequency and reattachment. Although ROCK inhibitors may be effective in reducing adherent tumor cell behavior, our results indicate that they could inadvertently increase metastatic potential of non-adherent CTCs by increasing their reattachment efficacy.
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