BackgroundThe　role　of　TMEM176A　in　human　hepatocellular　carcinoma　(HCC)　is　unknown.　This　study　explored　the　epigenetic　regulation　and　function　of　TMEM176A　in　human　HCC.Materials　and　methodsTwelve　HCC　cell　lines　and　126　cases　of　primary　cancer　were　analyzed.　Methylation-specific　PCR,　immunohistochemistry,　flow　cytometry,　and　xenograft　mouse　models　were　employed.ResultsTMEM176A　was　highly　expressed　in　SNU387,　SNU182,　Huh1,　and　SNU475　cells;　reduced　expression　was　observed　in　HepG2　and　PLC/PRF/5　cells;　and　no　expression　was　found　in　SNU449,　HBXF344,　SMMC7721,　Huh7,　and　LM3　cells.　Unmethylation　of　the　TMEM176A　promoter　was　detected　in　SNU387,　SNU182,　Huh1,　and　SNU475　cells;　partial　methylation　was　observed　in　HepG2　and　PLC/PRF/5　cells;　and　complete　methylation　was　found　in　SNU449,　HBXF344,　SMMC7721,　Huh7,　and　LM3　cells.　Upon　treatment　with　5-Aza-2-deoxycytidine,　re-expression　of　TMEM176A　was　detected　in　SNU449,　HBXF344,　SMMC7721,　Huh7,　and　LM3　cells;　increased　expression　of　TMEM176A　was　observed　in　HepG2　and　PLC/PRF/5　cells;　and　no　expression　changes　were　found　in　SNU387,　SNU182,　Huh1,　and　SNU475　cells.　The　TMEM176A　promoter　region　was　methylated　in　75.4%　(95/126)　of　primary　human　HCC.　Reduced　expression　of　TMEM176A　was　associated　with　promoter　region　methylation　(P＜0.05).　No　association　was　found　between　TMEM176A　promoter　methylation　and　age,　gender,　HBV　infection,　liver　cirrhosis,　tumor　size,　lymph　node　metastasis,　vessel　cancerous　embolus,　number　of　lesions,　and　TNM　stage　(all　P＞0.05).　These　results　demonstrated　that　the　expression　of　TMEM176A　is　regulated　by　promoter　region　methylation.　Methylation　of　the　TMEM176A　promoter　was　significantly　associated　with　tumor　cell　differentiation　(P＜0.05)　and　was　an　independent　prognostic　factor　for　poor　3-year　overall　survival　(OS,　P＜0.05).　TMEM176A　expression　induced　cell　apoptosis;　inhibited　cell　proliferation,　migration,　and　invasion;　suppressed　human　HCC　cell　xenograft　growth　in　mice;　and　inhibited　ERK　signaling　in　HCC　cells.ConclusionThe　promoter　region　of　TMEM176A　is　frequently　methylated　in　human　HCC,　and　the　expression　of　TMEM176A　is　regulated　by　promoter　region　methylation.　Methylation　of　the　TMEM176A　promoter　may　serve　as　a　diagnostic　and　prognostic　marker　in　HCC.　TMEM176A　suppresses　HCC　growth　by　inhibiting　the　ERK　signaling　pathway.