1. ¹Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
2. ²Winship Cancer Institute, Department of Dermatology, Emory University School of Medicine, Atlanta, Georgia, USA
3. ³Department of Surgery, University of Florida School of Medicine, Gainesville, Florida, USA
4. ⁴Department of Surgery and Winship Cancer Institute, Emory University School of Medicine, Atlanta, Georgia, USA

Correspondence: Jack E. Arbiser, Department of Dermatology, Winship Cancer Institute, Emory University School of Medicine, WMB 5309, 101 Woodruff Circle, Atlanta, Georgia 30322, USA. E-mail: jarbise@emory.edu

Received 18 May 2007; Revised 13 June 2007; Accepted 16 June 2007; Published online 4 October 2007.

Abstract

The Shb adapter protein is an Src homology 2-domain containing signaling intermediate operating downstream of several tyrosine kinase receptors, including vascular endothelial growth factor receptor-2. Shb is multifunctional and apoptosis is one response that Shb regulates. Inhibition of angiogenesis can be used in cancer therapy, and one way to achieve this is by inducing endothelial cell apoptosis. The angiosarcoma cell line SVR is of endothelial origin and can be used as a tool for studying in vivo inhibition of angiogenesis, and we thus employed an Shb-knockdown strategy using an inducible lentiviral system to reduce Shb levels in SVR cells and to study their responses. Shb knockdown increases the susceptibility of SVR cells to the apoptotic agents, cisplatin and staurosporine. Simultaneously, Shb knockdown causes reduced focal adhesion kinase (FAK) activation, monitored as phosphorylation of the regulatory residues tyrosines 576/577. No detectable effects on Akt or extracellular signal-regulated kinase activity were noted. The altered FAK activity coincided with an elongated cell phenotype that was particularly noticeable in the presence of staurosporine. In order to relate the effects of Shb knockdown to in vivo tumorigenicity, cells were exposed to the angiogenesis inhibitor honokiol, and again the cells with reduced Shb content exhibited increased apoptosis. Tumor growth in vivo was strongly reduced in the Shb-knockdown cells upon honokiol treatment. It is concluded that Shb regulates apoptosis and cell shape in tumor endothelial cells via FAK, and that Shb is a potential target for inhibition of angiogenesis.