Osteopontin influences cell migration dynamics in human salivary gland cancer

Salivary gland cancer although rare, is a disease with a high mortality rate, and a survival rate ranging from 20 to 40% at five or more years after diagnosis. A family of secreted glycoproteins known as SIBLING proteins has shown potential to be viable biomarkers in human salivary gland cancer. SIBLINGs are small, integrin-binding ligands with a soluble RGD motif that are expressed in mineralized tissue such as bone and teeth, and also in epithelial cells. They include DMP-1, DSPP, BSP, MEPE, and OPN. In human epithelial cancers such as breast, lung, and prostate, these proteins are known to play an important role in cell survival, proliferation, and migration. Our study of SIBLING proteins as potential biomarkers suggest that osteopontin (OPN) may be responsible for enhancing cancer progression. The current study focuses on the role of OPN in the microenvironment of human salivary gland cancer cells, especially with regard to cancer cell migration. Evaluation of cancer tissue samples, cancer cell lines, and the cancer extracellular matrix indicate that OPN is present in abundance. Our evaluation of OPN’s role in influencing cell migration reveals that OPN may be responsible for cell spreading characteristics, as well the enhanced cell migration seen in cancer. Additionally, silencing the expression of OPN resulted in abrogating specific changes seen in human salivary gland cancer cell migration. The data suggest that OPN has a very critical role to play in progression and potential metastasis of human salivary gland cancers, and could serve as a valuable prognostic indicator.