Mechanisms of tumor induction by human retroviruses

Oncogenesis can be induced by chronic and acute RNA tumor viruses through a promoter/enhancer insertion mechanism and through a transforming protein coded by a viral oncogene (v-onc), respectively. A hypothetical trans-activating mechanism is invoked by retroviruses with trans-activating regulatory proteins. So far, in humans only HTLV-I has been firmly linked to a malignancy. The same virus is also implicated in slowly progressing neurological disorders. Except for transformation by viral oncogenes, these mechanisms give rise to monoclonal tumors.