Human epidermal growth factor receptor 2 (HER2) is a type of membrane glycoprotein, and belongs to the epidermal growth factor (EGF) receptor family. HER2 plays a key role in development, cell proliferation and differentiation. HER2 has been reported to associate with malignancy and a poor prognosis in numerous carcinomas, including breast, prostate, ovarian, lung cancers and so on. HER2 is activated by dimerization and not activated by EGF, TGF-alpha and amphiregulin. Interaction with PTK6 increases its intrinsic kinase activity.It is heterodimer with EGFR, ERBB3 and ERBB4. HER2 associates with the 5'-TCAAATTC-3' sequence in the PTGS2/COX-2 promoter and activates its transcription. It implicated in transcriptional activation of CDKN1A and the function of the protein involves STAT3 and SRC. And also it involved in the transcription of rRNA genes by RNA Pol I and enhances protein synthesis and cell growth.