The role of human herpesvirus-8, (HHV-8), in multiple myeloma pathogenesis

Kaposi's sarcoma and other manifestations of human herpesvirus 8

Kaposi's sarcoma (KS) was described by Moritz Kaposi in 1872 and was known for an entire century as a rare disorder of older men usually of Eastern European, Mediterranean, and/or Jewish origin. In the early 1980s, the prevalence of KS began to increase dramatically and soon became the most common malignancy in patients with AIDS, especially those who were male homosexuals. In 1994, a new human herpesvirus (HHV) was found to be present in almost 100% of KS lesions. This virus was found to be a gammaherpesvirus, closely related to Epstein-Barr virus, and was designated HHV-8. Subsequently, HHV-8 DNA was found in almost all specimens of classic KS, endemic KS, and iatrogenic KS, as well as epidemic KS (ie, AIDS KS). It is now believed that HHV-8 is necessary, but not sufficient, to cause KS and that other factors such as immunosuppression play a major role. The use of highly active antiretroviral therapy (HAART) since 1996 has markedly reduced the prevalence of AIDS KS in western countries, but because 99% of the 40 million patients with AIDS in the world cannot afford HAART, KS is still a very common problem. Primary effusion lymphoma and multicentric Castleman's disease are also thought to be due to HHV-8. Although HHV-8 DNA has been described in a number of other cutaneous disorders, there is little evidence that HHV-8 is of etiologic significance in these diseases. The mechanism by which HHV-8 causes KS, primary effusion lymphoma, and multicentric Castleman's disease is not well understood but is thought to involve a number of molecular events, the study of which should further our understanding of viral oncology. (J Am Acad Dermatol 2002;47:641-55.)

LEARNING OBJECTIVE

At the completion of this learning activity, participants should be familiar with Kaposi's sarcoma and other manifestations of human herpesvirus 8.

HHV-8 encoded vIRF-1 represses the interferon antiviral response by blocking IRF-3 recruitment of the CBP/p300 coactivators

Human herpes virus 8 (HHV-8) has developed unique mechanisms for altering cellular proliferative and apoptotic control pathways by incorporating viral homologs to several cellular regulatory genes into its genome. One of the important pirated genes encoded by the ORF K9 reading frame is a viral homolog of the interferon regulatory factors (IRF), a family of cellular transcription proteins that regulates expression of genes involved in pathogen response, immune modulation and cell proliferation. vIRF-1 has been shown to downregulate the interferon- and IRF-mediated transcriptional activation of ISG and murine IFNA4 gene promoters. In this study we demonstrate that vIRF-1 efficiently inhibited virus-induced expression of endogenous interferon B, CC chemokine RANTES and CXC chemokine IP-10 genes. Co-expression analysis revealed that vIRF-1 selectively blocked IRF-3 but not IRF-7-mediated transactivation. vIRF-1 was able to bind to both IRF-3 and IRF-7 in vivo as detected by coimmunoprecipitation analysis, but did not affect IRF-3 dimerization, nuclear translocation and DNA binding activity. Rather, vIRF-1 interacted with the CBP/p300 coactivators and efficiently inhibited the formation of transcriptionally competent IRF-3-CBP/p300 complexes. These results illustrate that vIRF-1 is able to block the early stages of the IFN response to virus infection by interfering with the activation of IRF-3 responsive, immediate early IFN genes.