Alendronate-induced disruption of actin cytoskeleton and inhibition of migration/invasion are associated with cofilin downregulation in PC-3 prostate cancer cells

// Sanna S. Virtanen 1, 2 , Tamiko Ishizu 1 , Jouko A. Sandholm 3 , Eliisa Loyttyniemi 4 , H. Kalervo Vaananen 1 , Johanna M. Tuomela 1 and Pirkko L. Harkonen 1 1 University of Turku, Institute of Biomedicine, FI-20520 Turku, Finland 2 Turku University of Applied Sciences, Health and Well-being, FI-20520 Turku, Finland 3 Cell Imaging Core, Turku Centre for Biotechnology, University of Turku and Abo Akademi University, FI-20521 Turku, Finland 4 University of Turku, Department of Biostatistics, FI-20520 Turku, Finland Correspondence to: Sanna S. Virtanen, email: Sanna.Virtanen@turkuamk.fi Keywords: bisphosphonate; prostate cancer; invasion; actin cytoskeleton; cofilin Received: March 13, 2017     Accepted: July 28, 2018     Published: August 24, 2018 ABSTRACT Bisphosphonates are used for prevention of osteoporosis and metastatic bone diseases. Anti-invasive effects on various cancer cells have also been reported, but the mechanisms involved are not well-understood. We investigated the effects of the nitrogen-containing bisphosphonate alendronate (ALN) on the regulation of actin cytoskeleton in PC-3 cells. We analyzed the ALN effect on the organization and the dynamics of actin, and on the cytoskeleton-related regulatory proteins cofilin, p21-associated kinase 2 (PAK2), paxillin and focal adhesion kinase. Immunostainings of cofilin in ALN-treated PC-3 cells and xenografts were performed, and the role of cofilin in ALN-regulated F-actin organization and migration/invasion in PC-3 cells was analyzed using cofilin knockdown and transfection. We demonstrate that disrupted F-actin organization and decreased cell motility in ALN-treated PC-3 cells were associated with decreased levels of total and phosphorylated cofilin. PAK2 levels were also lowered but adhesion-related proteins were not altered. The knockdown of cofilin similarly impaired F-actin organization and decreased invasion of PC-3 cells, whereas in the cells transfected with a cofilin expressing vector, ALN treatment did not decrease cellular cofilin levels and migration as in mock transfected cells. ALN also reduced immunohistochemical staining of cofilin in PC-3 xenografts. Our results suggest that reduction of cofilin has an important role in ALN-induced disruption of the actin cytoskeleton and inhibition of the PC-3 cell motility and invasion. These data also support the idea that the nitrogen-containing bisphosphonates could be efficacious in inhibition of prostate cancer invasion and metastasis, if delivered in a pharmacological formulation accessible to the tumors.