en 30555655 <p>Background: The Human Epidermal growth factor Receptor-3 (HER-3) is a member of ErbB receptor family and has deficient kinase activity. HER-3 should heterodimerize with other members of ErbB receptor family, especially with HER-2, to transduce downstream signaling pathways. HER-3 co-expresses with other ErbB receptors in different cancers and overexpresses while the oncogenic signaling pathways such as Jak/Stat, MAPK, and PI3K/Akt are activated and promoted. Here, the expression level of HER-3 was evaluated in Iranian gastric adenocarcinoma&#39;s patients and the effects of HER-3 knocking down was investigated on cell cycle and cell viability of human gastric adenocarcinoma cell line of MKN45.<br /> Methods: In this study, 38 paraffin-embedded surgical adenocarcinoma specimens and their marginal non-tumor tissue samples were collected. Total RNAs were extracted and cDNAs were synthesized. Finally, the expression level of HER-3 was evaluated by real time PCR approach. Moreover, the human adenocarcinoma cell line of MKN45 was transfected with siRNA against HER-3 and the effects of its down-regulation were evaluated using MTT assay and cell-cycle analysis.<br /> Results: The data obtained from this study revealed HER-3 is significantly overexpressed in gastric tumors rather than non-tumor marginal tissues. Also, it was found that the expression level of HER-3 is elevated with tumor depth of invasion. Moreover, HER-3 knocking down promotes cell accumulation in G2/M phase of cell cycle and decreases cell viability in MKN45 cells which suggests a potential role for HER-3 in gastric adenocarcinoma tumorigenesis.<br /> Conclusion: Taken together, these results emphasize the importance of HER-3 receptor in diagnosis and prognosis of gastric adenocarcinoma.</p> Epidermal growth factor, Gastric adenocarcinoma, HER-3, Iran 227 232 https://www.ajmb.org/En/Article.aspx?id=329 https://www.ajmb.org/PDF/En/FullText/329.pdf EhsanMokhtariDepartment of Biology, Faculty of Biological Sciences, Islamic Azad University, East Tehran Branch, Tehran, Iran1321HesamodinMokhtariInternational Campus, Shahid Sadoughi University of Medical Sciences, Yazd, Iran1322ElhamMoslemiDepartment of Biology, Faculty of Biological Sciences, Islamic Azad University, East Tehran Branch, Tehran, Iran1323