Objective Metastasis-associated protein 1(MTA1)has been reported to be upregulated in multiple malignancies and promotes cancer proliferation and metastasis.However,whether and how MTA1 promotes esophageal squamous cell carcinoma(ESCC)tumorigenesis has been unanswered.In this study,we explored the effects of MTA1 to ESCC tumorigenesis and development,and investigated its related mechanism.Methods MTA1 transgenic mice and wild type mice were allowed free access to drinking water containing 4-NQO(100 μ g/ml)for 16-week and fresh drinking water for additional 6 weeks to established ESCC tumorigenesis model and investigated whether MTA1 overexpression promoted mice ESCC tumorigenesis.MTA1-overexpressing and MTA1-silencing cell lines were established by transfected with Lenti-shMTA1,Lenti-MTA1,or Lenti-GFP.Colony formation and Real-Time cell kinetic analyzer xCELLigence(RTCA)assay were used to detect the effects of MTA1 to proliferation and growth of normal esophageal epithelial cells and ESCC cells in vitro.MTA1 knockdown and control cells were subcutaneously injected in the right armpit of each nude mouse to evaluate the role of MTA1 to proliferation of ESCC cells in vivo.Transwell assay was used to verify the role of MTA1 in promoting ESCC cells migration and invasion in vitro.Furthermore,the molecule mechanism of MTA1 regulating ESCC tumorigenesis and development was explored by RNA-sequencing(RNA-seq)analysis and western blot assay.MEK(PD0325901)or ERK(SCH772948)inhibitor were used to further proved that MTA1 promoting ESCC malignant phenotypes by activating MEK/ERK/p90RSK pathway.Immunohistochemistry(IHC)assay was used to detect the expression of different protein in xenograft and ESCC tissues.Results The results indicated that MTA1 was overexpressed in ESCC cells and clinical ESCC samples.MTA1 promoted tumorigenesis in 4-NQO-induced mice ESCC model.The average tumor numbers of MTA1-OE mice(4.63±1.11)(>1mm diameter)were significantly more than those of WT mice(2.88±1.17)in 4-NQO treated groups,IHC staining revealed higher Ki-67 in tumor cells of MTA1-OE mice.Overexpression of MAT1 in KYSE410 and KYSE450 cells increased the colony formation by 318.1%±3.8%and 17.2%±2.8%,the cell migration by 43.7%±12.3%and 66.6%±22.4%,and the invasive capacity by 37.5%±25.6%and 164.3±44.7%,respectively,while knocking down MTA1 in ESCC cells significantly decreased colony formation,invasion and migration in vitro and inhibited growth of xenograft tumor in vivo.RNA-sequencing(RNA-seq)analysis combined with western blot assay uncovered that MTA1 promotes carcinogenesis by enhancing MEK/ERK/p90RSK signaling.Phosphorylation of MEK,ERK and their downstream target p90RSK was significantly decreased after MTA1 knockdown in ESCC cells,while increased in MTA1-overexpressing cells.Moreover,colony formation,invasion and migration potential were dramatically suppressed when cells overexpressed MTA1 were treated with MEK or ERK inhibitors.Conclusions We have identified a novel function of MTA1 overexpressed in ESCC.MTA1 promoted tumorigenesis in 4-NQO-induced mice ESCC model,and increased colony formation and proliferation of normal esophageal epithelial cells.In terms of mechanism,MTA1 enhanced colony formation,migration and invasion of ESCC cells by activating MEK/ERK/p90RSK cascade,and blocking MEK/ERK/p90RSK by target inhibitors suppressed malignant characteristics of ESCC cells overexpressing MTA1 in vitro.Moreover,MTA1 knockdown could significantly inhibit the xenograft growth in vivo.Collectively,MTA1 plays a pivotal oncogenic role in ESCC carcinogenesis through promoting MEK/ERK/p90RSK cascade.MTA1 might serve as a candidate therapeutic target for blocking esophageal cancer initiation and development.