Methods to Investigate Thrombin Cleavage of Osteopontin (OPN)

Osteopontin (OPN) is a matricellular protein containing binding sites for a variety of ligands including an RGD sequence for binding to αvβ3 integrins. OPN is a conserved substrate for thrombin, the effector protease of the coagulation cascade. Thrombin cleaves OPN at a single site revealing new functionalities such as a previously cryptic α4β1 and α9β1 integrin-binding site. That integrin-binding site is abolished upon treatment with a basic carboxypeptidase. The thrombin cleavage of OPN has been demonstrated to play a role in regulating tumor growth. This report describes methods for production of full-length OPN as well as the enzymatically cleaved OPN fragments resulting from thrombin and carboxypeptidase treatments. Quantification procedures for the various OPN proteins are described as well as functional assays on mouse melanoma and myeloid cell lines.