Osteosarcoma cell-calcium signaling through tissue factor–factor VIIa complex and factor Xa

The cells responsible for bone formation express protease-activated receptors. Although serine protease thrombin has been shown to elicit functional responses in bone cells that impact on cell survival and alkaline phosphatase activity, nothing is known about tissue factor, factor VIIa, and factor Xa, the serine proteases that act upstream of thrombin in the coagulation cascade. This paper demonstrates that tissue factor is expressed in the osteoblast-like cell line SaOS-2 and, that tissue factor in a factor VIIa-bound complex induces a transient intracellular Ca2+ increase through protease-activated receptor-2. In SaOS-2 cells, factor Xa induced a sustained intracellular Ca2+ response, as does SLIGRL, a PAR2-activating peptide, and PAR-1-dependent cell viability.