Grp94 as a Target in Human Oral Carcinogenesis

Objectives: A number of Ca²⁺ binding proteins are thought to be implicated in establishing the malignant and metastatic phenotypes of various tumors. In the present study, to explore further the global changes in Ca²⁺ binding protein genes associated with OSCCs, we have employed a pathway-based approach by applying network development tools to expand on microarray analysis.

Methods: To characterize Ca²⁺ binding protein gene expression changes in oral squamous cell carcinomas (OSCCs), we compared gene expression profiles in OSCC-derived cell lines with normal oral tissues using microarray and network analysis. One hundred Ca²⁺ binding protein genes differentially expressed in OSCCs were identified, and genetic pathways associated with expression changes were generated. Among genes mapped to the highest significance network, glucose regulated protein 94 kDa (Grp94) was further evaluated for mRNA and protein expression in the OSCC cell lines, primary OSCCs, and oral premalignant lesions (OPLs).

Results: A significant (P<0.001) increase in Grp94 expression was observed in all cell lines compared to normal oral epithelium. In immunohistochemistry, highly expressed Grp94 was evident in primary OSCCs and OPLs, whereas corresponding normal tissues had very faint or absent of the immunoreactivity for the protein. Real-time quantitative reverse transcriptase-polymerase chain reaction data agree with the protein expression status. Moreover, the presence of overexpression of Grp94 in primary tumor was significantly (P<0.001) correlated with poor disease-free survival.

Conclusion: In summary, we found novel specific networks of the Ca²⁺ binding protein genes in OSCC cells and identified several candidate genes for molecular targeting, especially for Grp94. Our findings may contribute to an understanding of key biologic functions and pathways of certain Ca²⁺ binding protein genes associated with OSCC and should stimulate further investigation into Ca²⁺ binding protein genes relevant to oral carcinogenesis.