¹Department of Orthopaedic Surgery, Graduate School of Medical and Dental Sciences, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima 890-8520, Japan

Correspondence: Dr T Setoguchi, E-mail: setoro@m2.kufm.kagoshima-u.ac.jp

²These authors contributed equally to this work

Received 9 January 2009; Revised 19 March 2009; Accepted 30 March 2009; Published online 19 May 2009.

Abstract

The study shows constitutive activation of the Notch pathway in various types of malignancies. However, it remains unclear how the Notch pathway is involved in the pathogenesis of osteosarcoma. We investigated the expression of the Notch pathway molecules in osteosarcoma biopsy specimens and examined the effect of Notch pathway inhibition. Real-time PCR revealed overexpression of Notch2, Jagged1, HEY1, and HEY2. On the other hand, Notch1 and DLL1 were downregulated in biopsy specimens. Notch pathway inhibition using -secretase inhibitor and CBF1 siRNA slowed the growth of osteosarcomas in vitro. In addition, -secretase inhibitor-treated xenograft models exhibited significantly slower osteosarcoma growth. Cell cycle analysis revealed that -secretase inhibitor promoted G1 arrest. Real-time PCR and western blot revealed that -secretase inhibitor reduced the expression of accelerators of the cell cycle, including cyclin D1, cyclin E1, E2, and SKP2. On the other hand, p21^cip1 protein, a cell cycle suppressor, was upregulated by -secretase inhibitor treatment. These findings suggest that inhibition of Notch pathway suppresses osteosarcoma growth by regulation of cell cycle regulator expression and that the inactivation of the Notch pathway may be a useful approach to the treatment of patients with osteosarcoma.