184 Beneficial and Detrimental Effects of Human Endogenous Retroviruses (HERVs)

Abstract

There has been significant recent progress in the elucidation of structure and function of HERVs, especially of their evolutionarily youngest member, HERV-K. Knowing more about structure and function allows a more solid analysis of the benefits HERVs may possess for humans or the damage they may cause. We will discuss recently recognized properties of HERV-K elements and expressed proteins and describe their established and putative roles in gene regulation, evolution and in cancer. A number of expressed envelope protein of several HERVs are bone fide fusion machines able to mediate cell entry and pseudotype lentiviruses. Moreover, its profound expression in placental trophoblasts contributes to syncytia formation and the immunosuppressive domains in the transmembrane subunits might subdue maternal immune responses in this organ to protect embryonic tissue. The accessory Rec protein is highly expressed in several tumors. It not only enhances nucleo-cytoplasmic transport of viral transcripts but also disturbs signaling pathways regulating cellular proliferation. The underlying mechanisms potentially leading to transformation or tumor promotion are already partially revealed. Moreover, large scale transcriptome analyses disclose more and more cases of significant gene disregulation on the one hand and beneficial domestication of several HERV elements on the other.