Oral squamous cell carcinoma (OSCC) has emerged as one of the major malignant tumors of
the head and neck cancers. However, the molecular mechanism behind tumorigenesis of OSCC is not fully
understood. The aim of this study was to investigate the role of calreticulin (CRT), an endoplasmic
reticulum-resident protein, in OSCC cells.
Materials and methods: Sixteen paired samples of tumor and non-cancerous matched tissue (NCMT), six
OSCC cell lines and normal human oral keratinocytes (NHOKs), and oral tissue microarray were used to
reveal the expression of CRT by Western blotting and immunohistochemistry. Later, shRNA-mediated
stable knockdown of CRT in OSCC cells was generated. The knockdown cell line was used to analyze cell
proliferation, colony formation, anchorage-independent growth and cell migration in vitro.
Results: CRT was differentially expressed in fresh tumor samples and six OSCC cell lines but not adjacent
NCMTs and NHOKs. In oral tissue microarray, we showed that there was positive CRT staining in the vast
majority of tumor cases (99/103), in sharp contrast to that in NCMT cases (29/92) (p < 0.001). Stable
knockdown of CRT in oral cancer cells resulted in significantly reduced growth rate, colony-forming
capacity and anchorage-independent growth. This may be attributed to the induction of G0/G1 cell cycle
arrest when CRT was depleted in the cells. Both horizontal and vertical movements of the CRTknockdown
stable line were markedly impaired. The phosphorylation levels of focal adhesion kinase
(FAK), paxillin and ERK1/2 and the activity of matrix metalloproteinase-2 and -9 (MMP-2 and MMP-9)
were decreased in the CRT-knockdown cells. These results suggest that CRT can regulate oral cancer cell
migration through activation of the FAK signaling pathway accompanied with proteolytic degradation of
the extracellular matrix (ECM) by MMP-2 and MMP-9.
Conclusion: Together, this study has defined a novel biological role for CRT in oral cancer. CRT is a potential
biomarker and may contribute to the malignant phenotypes of OSCC cells.
