Downregulation Of VAP-1 Suppresses The Progression Of Oral Squamous Cell Carcinoma And Reduces Neutrophil Infiltration In Tumor Microenvironment

Background and Objective: Vascular adhesion protein-1(VAP-1)is a unique molecule since it acts as an adhesion molecule as well as an ectoenzyme catalyzing oxidative deamination of primary amines.As VAP-1 participates in the transformation of sites of leukocyte rolling,adhesion,and transmigration into sites of inflammation,most studies of VAP-1 have focused on its inflammatory properties.VAP-1 activity is now considered a potential target for anti-inflammatory therapy.Other studies have shown that VAP-1 expression is higher in tumors than in normal tissues and has a correlation with disease stage,patient survival and poorer prognosis in tumors.Studies suggest that VAP-1-mediated activation dependent upon nuclear factor-κB(NF-κB)and lead to secretion of the chemokine interleukin 8(IL-8).However,whether NF-κB is also activated in tumors has not been reported.Our previous study found that overexpression expression of IL-8 and infiltrated neutrophils in the oral cancer microenvironment have promoted the progression of oral cancer.But whether VAP-1 is involved in the regulation of this process has not been elucidated.Therefore,this study aimed to explore the role of VAP-1 on the growth and metastasis of oral squamous cell carcinoma(OSCC)and its possible mechanism,and further explored whether VAP-1 is involved in regulating the expression of IL-8 and the migration ability of neutrophils in tumor microenvironment(TME).This study provides a new research idea for developing the mechanism of oral cancer progression and offers a promising strategy for cancer therapy.Methods: Immunochemistry staining was used to observe VAP-1 expression in OSCC tissues.VAP-1 was inhibited by si RNA in OSCC cells.We examined the effect of silencing VAP-1 on cell proliferation,migration and invasion by CCK8 and TRANSWELL assays.OSCC xenograft mouse model was established to examine the therapeutic efficacy of the VAP-1 inhibitor in vivo.RT q PCR and western blot analysis were used to examine NF-κB and IL-8 expression in OSCC cells and OSCC xenograft tumors.IL-8 expression in the supernatant of OSCC cells was examined by ELISA assays.VAP-1 and neutrophils in human OSCC tissues were examined by immunofluorescence staining.The migration ability of neutrophils was detected by TRANSWELL assay.Infiltrated neutrophils in OSCC xenograft tumors were examined by immunofluorescence staining.Results:(1)Immunohistochemical staining showed that VAP-1 was overexpressed in human OSCC tissues,and the expression of VAP-1 in specimens from patients with lymph node metastasis was higher than that in non-metastatic tissues;(2)When downregulation of VAP-1 in OSCC cells,the proliferation,migration and invasion ability of OSCC cells were inhibited;(3)The in vivo data from the xenograft mice models proved that VAP-1 inhibitor administration suppressed the tumor growth and lymph node metastasis;(4)Downregulation of VAP-1 in OSCC cells,the mRNA and protein levels of NF-κB and IL-8 were decreased,and the amount of IL-8 secreted in the cell supernatant was also decreased;(5)The expression of mRNA and protein levels of NF-κB and IL-8 in OSCC xenograft tumors after treatment with the VAP-1inhibitor were reduced;(6)Immunofluorescence staining showed that expression of VAP-1 and neutrophils were significantly higher in OSCC tissues than in normal mucosa;(7)Downregulation of VAP-1 in OSCC cells,the migration ability of neutrophils was weakened;(8)Immunofluorescence staining showed that neutrophil infiltration in OSCC xenograft tumors was reduced by VAP-1 inhibitor administration.Conclusions: Downregulation of VAP-1 suppresses tumor growth and metastasis in OSCC and reduces neutrophil infiltration in tumor microenvironment and the mechanism may involve in NF-κB/IL-8 signaling pathway.