Immune evasion in Kaposi's sarcoma-associated herpes virus associated oncogenesis. Semin Cancer Biol. 2008;18:423-436. [PMID: 18948197 DOI: 10.1016/j.semcancer.2008.09.003]

Update on HHV-8-Associated Malignancies

The human herpesvirus 8 (HHV-8) is the oncogenic virus associated with Kaposi's sarcoma (KS) and lymphoproliferative disorders, namely, primary effusion lymphoma and multicentric Castleman's disease. KS is among the most common malignancies seen in HIV-infected patients despite the decreased incidence of KS in the era of highly active antiretroviral therapy. Advances in molecular pathology reveal HHV-8 tumorigenesis is mediated through molecular mimicry wherein viral-encoded proteins can activate several cellular signaling cascades while evading immune surveillance. This knowledge has led to the evolution of multiple therapeutic strategies against specific molecular targets. Many such therapeutic modalities have shown activity, but none have proven to be curative. Identifying possible prognostic factors is another active area of research. This review summarizes the recent developments in the fields of virus transmission, molecular biology, and treatment of HHV-8-related neoplasms.

Influence of electrostatics on the complement regulatory functions of Kaposica, the complement inhibitor of Kaposi's sarcoma-associated herpesvirus

Kaposica, the complement regulator of Kaposi's sarcoma-associated herpesvirus, inhibits complement by supporting factor I-mediated inactivation of the proteolytically activated form of C3 (C3b) and C4 (C4b) (cofactor activity [CFA]) and by accelerating the decay of classical and alternative pathway C3-convertases (decay-accelerating activity [DAA]). Previous data suggested that electrostatic interactions play a critical role in the binding of viral complement regulators to their targets, C3b and C4b. We therefore investigated how electrostatic potential on Kaposica influences its activities. We built a homology structure of Kaposica and calculated the electrostatic potential of the molecule, using the Poisson-Boltzmann equation. Mutants were then designed to alter the overall positive potential of the molecule or of each of its domains and linkers by mutating Lys/Arg to Glu/Gln, and the functional activities of the expressed mutants were analyzed. Our data indicate that 1) positive potential at specific sites and not the overall positive potential on the molecule guides the CFAs and classical pathway DAA; 2) positive potential around the linkers between complement control protein domains (CCPs) 1-2 and 2-3 is more important for DAAs than for CFAs; 3) positive potential in CCP1 is crucial for binding to C3b and C4b, and thereby its functional activities; 4) conversion to negative or enhancement of negative potential for CCPs 2-4 has a marked effect on C3b-linked activities as opposed to C4b-linked activities; and 5) reversal of the electrostatic potential of CCP4 to negative has a differential effect on classical and alternative pathway DAAs. Together, our data provide functional relevance to conservation of positive potential in CCPs 1 and 4 and the linkers of viral complement regulators.

The inflammatory component of Kaposi sarcoma

Kaposi sarcoma (KS) is intimately linked to several aspects of the host immune system. KS development is linked to immunodeficiency in several clinical-epidemiological settings. The development of KS at local inflammatory sites has also been documented. Inflammatory cells are almost always present within KS lesions. Depending upon the inflammatory milieu, KS lesions may progress or regress. Not surprisingly, iatrogenic manipulation of host immunity with drugs may provoke KS growth and/or flare. Given the close association between KS and the immune system, the etiologic agent Kaposi Sarcoma Herpesvirus has developed a variety of mechanisms to evade the host immune system, all of which have cleverly evolved to promote oncogenesis and viral persistence.