Human endogenous retrovirus type K encoded Np9 oncoprotein induces DNA damage response

Human endogenous retrovirus sequences (HERVs) constitute up to 8% of the human genome, yet not all HERVs remain silent passengers within our genomes. Some HERVs, especially the HERV type K (HERV-K), have been found to be frequently transactivated in a variety of inflammatory diseases and human cancers. Np9, a 9-kDa HERV-K encoded protein, has been reported as an oncoprotein and found present in a variety of tumors and transformed cells. In the current study, we for the first time reported that ectopic expression of Np9 protein was able to induce DNA damage response from host cells especially through upregulation of γH2AX. Furthermore, we found that direct knockdown of Np9 by RNAi in Kaposi's Sarcoma-associated herpesvirus (KSHV) infected cells effectively reduced LANA expression, the viral major latent oncoprotein in vitro and in vivo, which may represent a novel strategy against virus-associated malignancies.