1α,25(OH) 2 D 3 Induces Actin Depolymerization in Endometrial Carcinoma Cells by Targeting RAC1 and PAK1

Abstract

Background: Cell proliferation and motility require actin reorganization, which is under control of various signalling pathways including ras-related C3 botulinum toxin substrate 1 (RAC1), p21 protein-activated kinase 1 (PAK1) and actin related protein 2 (ARP2). Tumour cell proliferation is modified by 1α,25-Dihydroxy-Vitamin D3 (1α,25(OH) 2 D 3 ), a steroid hormone predominantly known for its role in calcium and phosphorus metabolism. The present study explored whether 1α,25(OH) 2 D 3 modifies actin cytoskeleton in Ishikawa cells, a well differentiated endometrial carcinoma cell line. Methods: To this end, actin cytoskeleton was visualized by confocal microscopy. Globular over filamentous actin ratio was determined utilizing Western blotting and flow cytometry, transcript levels by qRT-PCR and protein abundance by immunoblotting. Results: A 24 hour treatment with 1α,25(OH) 2 D 3 (100 nM) significantly decreased RAC1 and PAK1 transcript levels and activity, decreased ARP2 protein levels and depolymerized actin. The effect of 1α,25(OH) 2 D 3 on actin polymerization was mimicked by pharmacological inhibition of RAC1 and PAK1. Conclusions: 1α,25(OH) 2 D 3 leads to disruption of RAC1 and PAK1 activity with subsequent actin depolymerization of endometrial carcinoma cells.