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Objective: Sunitinib, a targeted cancer drug, inhibits tyrosine kinases receptors and is widely used as first‐line treatment for metastatic renal cell carcinoma. Patients undergoing chemotherapy with sunitinib frequently have oral mucosal complications, such as oral stomatitis, though cytotoxic effects of the drug on oral keratinocytes remain unknown. Methods: The effects of sunitinib on immortalized oral keratinocytes, RT7 cells, in regard to cell injury and apoptosis, as well as apoptosis‐mediated signaling pathways were investigated. Results: Sunitinib treatment caused a significant increase in lactate dehydrogenase (LDH) in RT7 cells and primary oral keratinocytes. Additionally, the drug induced apoptosis‐related events, such as DNA fragmentation, decreased anti‐apoptotic Bcl‐2 protein expression, and induction of cleaved PARP and caspase 3/9 in RT7 cells. Furthermore, phosphorylation of p38 MAPK, but not of ERK or JNK, was increased. On the contrary, constitutive phosphorylated STAT3 was decreased by sunitinib treatment, which was recovered by exposure to SB203580, a p38 MAPK inhibitor. Finally, SB203580 was found to reduce sunitinib‐induced cell injury and apoptosis. Conclusion: The present results indicate that sunitinib promotes cell injury and apoptosis in oral keratinocytes via p38 activation and STAT3 downregulation. Sunitinib‐mediated oral complications may be associated with cytotoxic effects of the drug on oral keratinocytes. [ABSTRACT FROM AUTHOR]

Objectives: ACE2, known as a host receptor involved with SARS‐CoV‐2 infection, binds to viral spike proteins for host cell entry. However, details regarding its induction and function in oral mucosal cells remain unknown. Materials and Methods: We examined ACE2 expression and its induction by transfected mimic nucleotides and pro‐inflammatory cytokines in oral keratinocytes (RT7) and fibroblasts (GT1). Subsequently, the effects of viral spike S1 protein via ACE2 on CXCL10 expression induced by pro‐inflammatory cytokines in both cells were examined. Results: ACE2 was constitutively expressed in RT7 and GT1. Transfected Poly(I:C) and Poly(dA:dT) increased ACE2 expression in those cells, while knockdown of RIG‐I decreased ACE2 expression induced by those transfected ds nucleotides. IFN‐γ and TNF‐α enhanced transfected ds nucleotides‐induced ACE2 expression in RT7 but not GT1. S1 protein alone did not affect CXCL10 expression in either cell type, whereas it enhanced IFN‐β‐induced CXCL10 in both, while immune responses of IFN‐γ‐ and TNF‐α‐induced CXCL10 enhanced by S1 protein were different between RT7 and GT1. Finally, knockdown of ACE2 decreased cytokines and S1 protein mediated‐CXCL10 levels in both cells. Conclusions: ACE2 in oral mucosal cells may contribute to development of infection and inflammation in cooperation with pro‐inflammatory cytokines following SARS‐CoV‐2 invasion. [ABSTRACT FROM AUTHOR]

Recognition of nucleic acids as pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) promotes an inflammatory response. On the other hand, LL-37, an antimicrobial peptide, is a multifunctional modulator of immune response, though whether it modulates inflammatory responses induced by nucleic acids in oral keratinocytes is unknown. In this study, we firstly investigated the effect of LL-37 on CXCL10 induced by DAMPs and PAMPs in immortalized oral keratinocytes, RT7. Furthermore, the effects of LL-37 on translocation of exogenous nucleic acids into cytoplasm as well as cytosolic receptor, RIG-I on immune responses mediated by LL-37-nucleic acid complexes were examined. From these results, LL-37 enhanced necrotic cell supernatant (NCS)–induced CXCL10 expression in RT7, while the response was decreased by RNase. Complexes of LL-37 and double-stranded (ds) RNA, Poly(I:C) enhanced CXCL10 expression in comparison with each alone, which were associated with NF-κB activation. Furthermore, LL-37 was shown to bind with ds nucleotides and translocate into cytoplasm. Knockdown of RIG-I decreased expression of CXCL10 induced by LL-37-Poly(I:C) complexes, and RIG-I were co-localized with Poly(I:C) entered by LL-37 in cytoplasm. LL-37 modulates dsRNA-mediated inflammatory response via RIG-I in oral keratinocytes, which may play an important role in the pathogenesis of oral inflammatory diseases. [ABSTRACT FROM AUTHOR]

Background: Melatonin is a hormone that is primarily produced in the pineal gland and is involved in wide range of biological functions. However, the impact of melatonin on chemotherapy‐induced cell death remains to be elucidated in oral squamous cell carcinoma (OSCC) cells. The objective of this study was to clarify the role of melatonin in cisplatin‐induced cytotoxicity in CD44high OSCC cells. Methods: CD44high OSCC cells were cultured on fibronectin‐coated hydrogel. A lactate dehydrogenase cytotoxicity assay was performed to evaluate cisplatin‐induced cell death. The effect of melatonin on cisplatin‐induced cell death and Derlin‐1 (DERL1) endoplasmic reticulum membrane protein expression was investigated. Results: CD44high OSCC cells exhibited mesenchymal‐like features when cultured on fibronectin‐coated hydrogel. Mesenchymal‐like CD44high OSCC cells demonstrated strong resistance to cisplatin‐induced cell death compared with epithelial‐like CD44high OSCC cells. DERL1 mRNA and DERL1 protein expression levels were significantly higher in mesenchymal‐like CD44high cells compared with epithelial‐like CD44high cells. Cisplatin‐induced cell death was significantly enhanced after DERL1 siRNA knockdown, suggesting that DERL1 is involved in resistance to cisplatin‐induced cell death. Melatonin significantly inhibited DERL1 expression and enhanced cisplatin‐induced cell death in mesenchymal‐like CD44high cells. miR‐181c‐5p expression was significantly upregulated in the presence of melatonin. Furthermore, melatonin‐inhibited DERL1 expression was significantly recovered by miR‐181c‐5p inhibitor. In addition, melatoninenhanced cisplatin‐induced cell death was attenuated by miR‐181c‐5p inhibitor. These results suggest that melatonin‐induced miR‐181c‐5p enhances cisplatin‐induced cell death through inhibition of DERL1 in mesenchymal‐like CD44high cells. Conclusions: Melatonin plays a vital role in promoting cisplatin‐induced cytotoxicity in mesenchymal‐like CD44high OSCC cells. [ABSTRACT FROM AUTHOR]

Innate immune systems in the oral cavity have important roles in the host defense against viral invasion of oral mucosa. Poly(ADP-ribose) polymerase 13 (PARP13), which has a strong antiviral ability, has been reported to possess two isoforms; a full-length protein, zinc-finger antiviral protein long (ZAPL), and a shorter protein (ZAPS). However, the expression and function of these two isoforms in oral mucosa remain unknown. In the present study, the expression levels of ZAPL and ZAPS induced by transfected double-stranded (ds) RNA, Poly(I:C), and dsDNA, Poly(dA:dT), in immortalized oral keratinocytes and fibroblasts (RT7 and GT1 cell lines, respectively) were investigated. Subsequently, the effects of the knockdown of ZAPL and ZAPS on transfected nucleotide-induced antiviral factors were examined. The results demonstrated constitutive expression of ZAPL and ZAPS in RT7 and GT1 cells, and their expression in both cell types was notably increased by transfection of Poly(I:C) and Poly(dA:dT) when compared with no transfection. Specific knockdown of ZAPL and ZAPS in RT7 cells decreased IFN-β and C-X-C motif chemokine ligand 10 (CXCL10) expression induced by transfected Poly(I:C) and Poly(dA:dT). On the other hand, knockdown of ZAPL and ZAPS in GT1 cells decreased the expression of CXCL10 induced by the transfected nucleotides, whereas that had no effect on IFN-β expression induced by Poly(dA:dT). Their knockdown was also associated with transfected nucleotides-induced IFN regulatory factor 3 phosphorylation in both cell types. Taken together, these results indicate that ZAPL and ZAPS, isoforms of PARP13, in oral mucosal cells participate in host defense against viral infection of oral mucosa. [ABSTRACT FROM AUTHOR]