Inhibitor of Growth 4 (ING4) Plays a Tumor-repressing Role in Oral Squamous Cell Carcinoma via Nuclear Factor Kappa-B (NF-B)/DNA Methyltransferase 1 (DNMT1) Axis-mediated Regulation of Aldehyde Dehydrogenase 1A2 (ALDH1A2)

Background: Inhibitor of growth 4 (ING4) level was reported to he decreased in head and neck squamous cell carcinoma (HNSC) tissue, however, it is unknown whether and how ING4 participates in regulating the development of oral squamous cell carcinoma (OSCC). Objective: This study aimed to investigate the role and mechanism of ING4 in OSCC. Methods: ING4 was forced to up- or down-regulated in two OSCC cell lines, and its effects on the malignant behavior of OSCC cells were investigated in vitro. The ubiquitination level of NF-kappa B p65 in ING4 upregulated cells was measured by co-immunoprecipitation. Moreover, the effects of ING4 on the methylation level of ALDHIA2 were evaluated by methylation-specific polymerase chain reaction (MSP) assay. The role of ING4 in OSCC growth in vivo was observed in nude mice. Results: Our results showed that the expression of ING4 in OSCC cell lines was lower than that in normal oral keratinocyte cells. In vitro, ING4 overexpression inhibited the proliferation, migration, and invasion of OSCC cell lines and ING4 silencing exhibited opposite results. We also demonstrated that ING4 overexpression promoted the ubiquitination and degradation of P65 and reduced DNA methyl-transferase 1 (DNMT1) expression and Aldehyde dehydrogenase 1A2 (ALDHIA2) methylation. Moreover, overexpression of p65 rescued the suppression of malignant behavior, induced by ING4 overexpression. In addition, ING4 negatively regulated the growth of OSCC xenograft tumors in vivo. Conclusion: Our data evidenced that ING4 played a tumor-repressing role in OSCC in vivo and in vitro via NF-kappa B/DNMT1/ALDH1A2 axis.