Dean Kedes Research Interests
Dean Kedes Research Interests
The research in my laboratory focuses on a recently described human herpesvirus associated with Kaposi's sarcoma (KS), the most common AIDS-associated malignancy. This tumor has a complex pathology exhibiting mixed cellularity and abnormal angiogenesis and its genesis likely depends on viral replication within an immunologically impaired host. Epidemiological evidence has long implicated a transmissible agent in the etiology of Kaposi's sarcoma. Its high prevalence in homosexual men with AIDS and relative scarcity in their hemophiliac counterparts is one such suggestive observation. Kaposi's sarcoma-associated herpesvirus (KSHV) also termed human herpesvirus 8 (HHV-8) has been implicated by our work and that of others as the major etiologic agent in the development of this disease. In addition, KSHV, a gammaherpesvirus, is associated with a rare type of AIDS-associated body-cavity based B cell lymphoma (BCBL) also known as primary effusion lymphoma (PEL). These lymphomas have allowed the development of cell lines that, with appropriate stimuli, produce KSHV in culture.
Our investigations include two major areas. The first is the determination of the protein composition, spatial arrangement and assembly of both enveloped virions and subviral particles with special emphasis on the inner icosahedral capsid. This structure represents the completion of the first step in viral assembly and its formation is absolutely essential for replication. Our approaches include the coupling of classical molecular biology and biochemistry with electron microscopy (EM), immuno-EM and cryo-EM. The second is the isolation and characterization of viral genes and their protein products that are potentially involved in KSHV pathogenesis. In particular we are interested in the mechanisms underlying the virus's ability to evade host cell defenses, including apoptosis, the self-induced death of infected cells. We approach these aims by examining viral gene expression and viral-host protein interactions.
The capsid of Kaposi's sarcoma-associated herpesvirus (KSHV) was visualized at 24-A resolution by cryoelectron microscopy. Despite limited sequence similarity between corresponding capsid proteins, KSHV has the same T=16 triangulation number and much the same capsid architecture as herpes simplex virus (HSV) and cytomegalovirus (CMV). Its capsomers are hexamers and pentamers of the major capsid protein, forming a shell with a flat, close-packed, inner surface (the "floor") and chimney-like external protrusions. Overlying the floor at trigonal positions are (alpha beta(2)) heterotrimers called triplexes. The floor structure is well conserved over all three viruses, and the most variable capsid features reside on the outer surface, i.e., in the shapes of the protrusions and triplexes, in which KSHV resembles CMV and differs from HSV. Major capsid protein sequences from the three subfamilies have some similarity, which is closer between KSHV and CMV than between either virus and HSV. The triplex proteins are less highly conserved, but sequence analysis identifies relatively conserved tracts. In alphaherpesviruses, the alpha-subunit (VP19c in HSV) has a 100-residue N-terminal extension and an insertion near the C terminus. The small basic capsid protein sequences are highly divergent: whereas the HSV and CMV proteins bind only to hexons, difference mapping suggests that the KSHV protein, ORF65, binds around the tips of both hexons and pentons.