INTERFERON GAMMA (IFNΓ) ANTITUMOR EFFECTS ON ORAL CANCER CELLS ARE ACCOMPANIED BY ER STRESS RESPONSE MODULATION AND DSPP ACTIVITY SUPPRESSION

Abstract

Objectives Expression of proinflammatory cytokines in various malignant neoplasms is widely considered to represent a host immune response to control tumor development. Recently, the role of interferon gamma (IFNγ) in oral squamous cell carcinoma (OSCC) and its relation with endoplasmic reticulum (ER) stress pathways were investigated. Dentin sialophosphoprotein (DSPP) has been involved in malignant transformation, invasion and metastasis of OSCC. The present study examined the effects of IFNγ treatment on ER stress, Unfolded Protein Response (UPR) and calcium homeostasis regulating mechanisms and the potential interaction with DSPP in OSCC cells. Findings Oral cancer OSC2 cells were assessed following IFNγ treatment at specific time-points. DSPP and MMP20 mRNA expression levels, as well as ER stress, UPR and calcium homeostasis-related proteins, including GRP78, SERCA2b, IP3r, PERK and IRE1, were assayed by RT-PCR, while Bcl-2, Bax, PCNA and Cytochrome C protein expression levels were analyzed by Western blot. IFNγ treatment significantly downregulated mRNA levels of major ER stress regulator GRP78, and, to a lesser extent, UPR-related molecule IRE1, but without significant effect on PERK. Furthermore, IFNγ affected the mRNA expression levels of important ER calcium homeostasis molecules, downregulating SERCA2b and upregulating IP3r. Additionally, DSPP and MMP20 mRNA levels were significantly reduced by IFNγ. IFNγ treatment also hampered OSC2 migration (assessed by wound-healing assay), reduced cell viability (evaluated by MTT), and enhanced apoptosis (assayed by Annexin V/FITC flow cytometry). These changes were accompanied by induction of Bax and Cytochrome c and downregulation of PCNA and Bcl-2 protein levels. Conclusions IFNγ appears to inhibit oral cancer cell viability and migration, and drive apoptosis, possibly by regulating ER stress and UPR mechanisms. DSPP and MMP20 downregulation appears to correspond to the IFNγ-induced changes in ER calcium homeostasis in OSCC.