Cloning of hamster osteopontin and expression distribution in normal tissues and experimentally induced oral squamous-cell carcinoma

Osteopontin is Critical for Hyperactive mTOR-Induced Tumorigenesis in Oral Squamous Cell Carcinoma

Mechanistic target of rapamycin (mTOR) plays a critical role in the development of oral squamous cell carcinoma (OSCC), but the underlying mechanisms remain poorly understood. Here we have demonstrated that the expression of osteopontin (OPN) was dramatically up-regulated in OSCC tissues and cell lines. Moreover, reduction of OPN suppressed cell proliferation, colony formation, and in vivo tumorigenic ability of OSCC cell lines Tca8113. In addition, there was a strong positive correlation between mTORC1 activity and OPN expression in OSCC tissues and cell lines. Furthermore, mTOR complex 1 (mTORC1) enhanced OPN expression through up-regulation of ERRα. Therefore, OPN is a downstream target of mTORC1 and is crucial for OSCC development. mTORC1, ERRα, and OPN may be potential targets for treatment of OSCC with aberrant mTORC1 signaling.

Osteopontin gene expression determines spontaneous metastatic performance of orthotopic human breast cancer xenografts

A major problem in the therapeutic management of cancer is the growth of metastases in distant organs, but the genes orchestrating the process need to be identified for the rational design of new treatment. Here, we provide decisive experimental evidence demonstrating the causal involvement of a specific gene, osteopontin (OPN), in the pathogenesis of metastasis by human breast cancer cells and implicating some of its probable partners. Stable long-term depletion, or up-regulation, of OPN gene expression in a matched, isogenic pair of human breast cancer cell lines of differing metastatic proficiency reproducibly changed their ability to colonize distant organs. OPN down-regulation was achieved by transduction of the metastatic line with a DNA construct encoding a small hairpin RNA in a vector labeled with red fluorescent protein and resulted in a marked reduction of metastatic load (P < 0.01). Up-regulation of OPN in the negligibly metastatic line, with a green fluorescent protein-marked retroviral vector containing OPN cDNA driven by a strong promoter, resulted in heavy colonization of the lungs and lymph nodes (P < 0.005). The reciprocal changes in behavior of these matched cell lines cross-corroborate each other. Concomitant changes were seen in the expression of other metastasis-related genes in both modulated lines. The data indicate that therapeutic targeting of tumor OPN molecules could reset metastatically relevant gene networks, resulting in clinical benefit.

Up-regulation of SIBLING proteins and correlation with cognate MMP expression in oral cancer

Various combinations of the SIBLING family of proteins have been found to be up-regulated in many human cancers and have been linked to different stages of tumor progression, including metastasis. Bone sialoprotein (BSP), osteopontin (OPN) and dentin matrix protein 1 (DMP1) specifically bind and activate MMP-2, MMP-3, and MMP-9, respectively. These proteases have also been shown to play important roles in oral squamous cell carcinoma (OSCC) invasion and metastasis. However, with the exception of OPN, there are no reports on the expression of the family of five SIBLING proteins in OSCC. This study examines the expression patterns of the SIBLING family (and MMP partners when known) in OSCC, correlating expression to outcome variables. Archived paraffin sections of 87 cases of primary OSCC were screened by immunohistochemistry for the SIBLINGs and their MMP partners. Three SIBLINGs (BSP, DSPP, and OPN), were expressed in OSCC, while DMP1 and MEPE expression were never observed. Furthermore, BSP and OPN were always expressed with their known MMP partners, MMP-2 and MMP-3, respectively. Poorly differentiated tumors exhibited reduced or no immunoreactivity for BSP and OPN but increased immunoreactivity for DSPP. Seventy eight (90%) cases were positive for BSP and DSPP, while 79 cases (91%) were positive for OPN. Overall, 91% of the cases were positive for at least one SIBLING. There were no correlations between SIBLING expression and tumor size ("T"; of the Union Internationale Contre le Cancer [UICC]-TNM classification for OSCC), and between SIBLING expression and lymph node spread for the T1/T2 tumors. The levels of DSPP expression for floor of mouth and retromolar region tumors were higher than for tongue tumors. Statistically significant correlations were, however, found between the expression levels of BSP and MMP-2 (p<0.0001), BSP and MMP-3 (p<0.0001), and OPN and MMP-3 (p<0.0024). We conclude that BSP, DSPP, and OPN are highly up-regulated in OSCC. While the production of these SIBLINGs is independent of T, they correlate with oral location of tumor, cognate MMP expression, and for DSPP, the degree of tumor differentiation.