Human RecQ helicase family, consisting of RECQL, RECQL4, RECQL5, BIM and WRN, has critical roles in genetic stability and tumorigenesis. Although RECQL5 has been reported to correlate with the susceptibility to malignances including osteosarcoma, the specific effect on tumor genesis and progression is not yet clarified. Here we focused on the relationship between RECQL5 expression and osteosarcoma disease progression, and further investigated the function of RECQL5 on MG-63 cell proliferation and apoptosis. By immunohistochemical analysis, qRT-PCR and western blot, we found that RECQL5 expression was downregulated in osteosarcoma tissues and cells. Patients with advanced tumor stage and low grade expressed lower RECQL5. To construct a stable RECQL5 overexpression osteosarcoma cell line (MG-63-RECQL5), RECQL5 gene was inserted into the human AAVS1 safe harbor by CRISPR/Cas9 system. The overexpression of RECQL5 was verified by qRT-PCR and western blot. Cell proliferation, cell cycle and apoptosis assay revealed that RECQL5 overexpression inhibited proliferation, induced G1-phase arrest and promoted apoptosis in MG-63 cells. Collectively, our results suggested RECQL5 as a tumor suppressor in osteosarcoma and may be a potential therapeutic target for osteosarcoma treatment. (C) 2015 Elsevier Inc. All rights reserved.