Role Of HOXB9 In Regulation Of Proliferation And Metastasis Of Human Gastric Cancer

Background and purpose: Gastric cancer(GC)is one of the most common malignant tumors and the second leading cause of cancer death worldwide.In China,the morbidity and motality of gastric cancer are higher than those of other countries,therefore it is more important to improve early diagnosis and prognosis of GC.The outcome of GC has gradually improved,but the survival rate of patients with advanced GC is still disappointing,mainly due to the poor understanding of the molecular mechanism of gastric cancer development.The etiological factors and pathogenesis of gastric cancer are not yet fully understood,and its development is a complex,multistep process involving multiple genetic and epigenetic alterations in oncogenes,tumor suppressor genes,and signaling molecules.Identifing new molecules and signal passways involved in the carcinogenesis of GC will provide the theoretical base and research proof for the novel diagnosis and treatment for GC.HOX genes are a family of homeodomain-containing transcription factors that determine morphogenesis and differentiation during development.Members of Hox gene family were also reported to be close related to malignant tumors by regulating the progression of tumors.Recently,HOXB9,a member belongs to the B clusters of HOX genes,was paid more attention on its role in oncogenesis.HOXB9 can regulate the cancergenesis process in breast cancer and leukemia.To date,the role of HOXB9 in GC is not fully explored.Hence,we presume that the abnormal expression of HOXB9 may be related with the development of GC.The aim of this study is to elucidate the role of HOXB9 in GC and the molecular mechanism in gastric cancer carcinogenesis and development.Methods: The differential expression of HOXB9 in gastric cancer tissues,matched non-tumor tissues and GC cell lines was detected by immunohistochemistry staining,Quantitative real-time PCR and western blot.Then,the relationships between HOXB9 expression level and clinicopathologic variables were analysised.Lentivirus over-expressing HOXB9 and expressing HOXB9-target sh RNA was produced by plasmids.SGC7901 and BGC823 were infected by lentiviruses respectively to upregulate and knock down the expression of HOXB9,then biological effects including proliferation,cell cycle,apoptosis,metastasis and tumorigenicity were investigated in vitro and In vivo,meanwhile the expression of p-Akt,p-GSK3β,Caspase-3 and the expression change of EMT markers were investigated by western blot.Results: Level of HOXB9 protein was found down-regulated in gastric cancer tissues compared with its non-tumor tissues and the expression level of HOXB9 was negatively correlated with tumor size,lymph node metastasis and TNM stages.The expression of HOXB9 is down-regulated among GC cell lines.Overexpression of HOXB9 in gastric cancer cells SGC7901 markedly suppressed cell proliferation and induced apoptosis both in vitro and in vivo.Furthermore,we demonstrate that overexpression of HOXB9 also inhibited the expression of p-Akt and p-GSK3β,but not the expression of total Akt,meanwhile the expression of cleaved-Caspase3 was up-regulated.Knockdown of HOXB9 in BGC823 showed reversed results.Overexpression of HOXB9 markedly inhibited SGC7901 cells invasion and migration in vitro and metastasis in vivo.Moreover,the mesenchymal marker,N-Cadherin and Vimentin were also inhibited by HOXB9 and overexpressing HOXB9 up-regulated E-Cadherin,a notable marker of epithelial tissue.Down regulating HOXB9 promoted cell migration and invasion in vitro and In vivo,and inhibited E-cadherin,while increased the expression of N-Cadherin and Vimentin.Conclusions: The expression level of HOXB9 is downregulated in gastric cancer and is negatively correlated with tumor size,lymph node metastasis and TNM stages.Overexpression of HOXB9 in gastric cancer cells dramatically suppresses cell proliferation and induces cell apoptosis both under the possible mechanism of suppressing the Akt signaling pathway and activation of Caspase-3.HOXB9 inhibits cell metastasis both in vitro and in vivo is related to prevention of EMT of GC cells.