Klaus Früh, Ph.D.

Biography
Following undergraduate studies at the University of Konstanz and the University of Heidelberg, Dr. Klaus Früh received his Ph.D. from the University of Heidelberg in 1990 studying the immune response to the malaria parasite. He then spent four years as a postdoctoral fellow: one year at the Center for Molecular Biology in Heidelberg and three years at the Scripps Research Institute in La Jolla, CA where he studied molecular pathways of antigen presentation. Dr. Früh then became a Senior Scientist at the R.W. Johnson Pharmaceutical Research Institute, eventually becoming the Group Leader for Molecular Virology at the same company. During this time he developed research programs in viral immune modulation and in antiviral drug discovery. He joined OHSU in 2000 as an Associate Scientist at the VGTI and as Director of the Gene Microarray Shared Resource. Dr. Früh became full Professor for Microbiology and Immunology in 2006.

Research Overview
Our immune system is extremely efficient at fighting off viruses, yet some viruses are able to overcome innate or adaptive immune response mechanisms and create disease. We study the molecular mechanisms used by viruses to evade host immune responses. Most acute viral infections are eventually cleared by the immune system and generate long-lasting immunity. However, such viruses might cause significant morbidity, or even death in some instances. Examples of such viruses are flaviruses (Dengue, West Nile and Yellow Fever virus) and poxviruses (smallpox and monkeypoxvirus). However, other viruses establish a chronic infection whereby a balance is established in which the host's immune system controls, but is unable to eradicate the virus. Such viruses are often asymptomatic in immune competent individuals but cause disease upon immune suppression, e.g. in AIDS patients. Examples of such chronic infections are viruses of the herpesvirus family, e.g. cytomegalovirus and Kaposi’s sarcoma herpesvirus. Large DNA viruses, such as poxviruses and herpesviruses,  encode numerous, often host-related, modulators of the host’s immune response whereas small RNA viruses, such as flaviviruses, have a limited set of immune modulators but might additionally escape immune control by mutation. Our research aims at identifying the function of such viral gene products as well as their related host gene products. We are particularly interested in human and rhesus cytomegalovirus (CMV), Kaposi’s sarcoma herpesvirus (KSHV), West Nile Virus and the orthopoxviruses Cowpoxvirus and Monkeypoxvirus. To characterize how these viruses manage to escape or delay immunity we apply the whole arsenal of modern molecular biology, functional genomics, genetics, cell imaging and in vivo models. Stripping viruses of their stealth mechanisms will be a new approach to anti-viral therapy and vaccine development. Additionally, viral immune modulatory protein can be used to modulate unwanted auto-immune responses.

Inhibition of antigen presentation
The intricate balance between the host's ability to control the virus and the virus' defense measures is illustrated by the many different viral mechanisms to escape the detection of infected cells by cytotoxic T cells which destroy virally infected cells in tissues. Infected cells are recognized via the T cell receptor that "sees" viral peptides presented by major histocompatibility complex class I (MHC I) molecules on the cell surface. The process by which viral fragments are presented at the cell surface is shown in Figure 1 . Since viruses evolved under the selective pressure of the MHC system, both herpesviruses and poxviruses developed counter defense mechanisms against antigen presentation (reviewed in Früh et al. 1999, and Früh et al. Virus Res 88(1-2), 55-69 (2002)). A focus of the laboratory is therefore to identify and characterize viral inhibitors of antigen presentation and examine the role of these inhibitors for viral infection.

Immune modulation by Cytmegalovirus
CMVs are among the most successful viruses since they manage to establish themselves in a large part of the population (up to 90%) and remain in the host for life despite enormous CMV-specific immune responses. Both human and rhesus CMVs encode several gene products of the US6 glycoprotein family that independently interfere with MHC class I antigen presentation (Pande et al. J Virol 79(9), 5786-98 (2005)) (Figure 2). The US2 protein and the US11 protein mediate the proteasomal degradation of newly synthesized MHC class I molecules. US3 retains assembled proteins in the lumen of the endoplasmic reticulum. US6 inhibits peptide translocation by the TAP transporter. In addition, we discovered a novel MHC-I inhibitory mechanism encoded by rhesus CMV, but not HCMV, which seems to act prior to the US6-family proteins. Current work aims at characterizing this novel mechanism and identifying the responsible gene product. Using the rhesus model we are also studying the role of these immune modulators in vivo.
A second aspect of our studies of CMV is the evasion of innate immune responses, particularly interferon responses, by rhesus and human CMV (see page by Dr. Victor DeFilippis).

Immune modulation and tumorigenesis by Kaposi’s sarcoma herpesvirus
KSHV encodes two proteins, K3 and K5, which inhibit antigen presentation by MHC I. K3 and K5 are transmembrane RING-type ubiquitin ligases that ubiquitinate the MHC I molecule resulting in their internalization and lysosomal destruction (Figure 3). Interestingly, vertebrate and non-vertebrate genomes contain genes of hitherto unknown function that are homologous to K3 and K5 which we named membrane-associated RING-CH (MARCH) proteins (Bartee J Virol 78(3), 1109-20 (2004). Current work aims at elucidating the function of these MARCH proteins. To identify the targets of these ubiquitin ligases we developed a quantitative proteomics approach to monitor the changes in the plasma-membrane proteome (Bartee PLoS Pathog 2(10), e107 (2006)). Using this and other approaches we identified novel cellular targets for MARCH proteins as well as their viral homologues. For instance, we reported that the KSHV protein K5 eliminates the intercell adhesion molecule CD31/PECAM-1 from the surface of endothelial cells, a cell type that is transformed in Kaposi’s sarcoma (Mansouri Blood 108(6), 1932-40 (2006)). This and other work demonstrates that K5 introduces profound changes into the plasma membrane proteome of virally infected endothelial cells. These proteomic changes occur in addition to changes in the cellular transcriptome which were observed by DNA microarrays in an in vitro model of Kaposi’s sarcoma (Moses J Virol 76(16), 8383-99. (2002). Based on these array studies we used a combination of DNA microarrays, antisense molecules and small interfering RNAs to identify host cell pathways that are dysregulated during KSHV-mediated tumorigenesis (Rose Oncogene 26(14), 1995-2005 (2007); Rose J. Virol. in press (2007); Raggo Cancer Res 65(12), 5084-95 (2005)). This work is done in collaboration with Dr. Ashlee Moses. .

Immune modulation by poxviruses
Members of the Yatapoxvirus and leporipoxvirus family encode homologues of MARCH protein family of transmembrane ubiquitin ligases that interfere with antigen presentation and T cell stimulation (Mansouri  J Virol 77(2), 1427-40 (2003). While such RING-CH proteins are not found in orthopoxvirus genomes, all poxviruses encode a second RING protein, p28, which acts as ubiquitin ligase (Nerenberg J Virol 79(1), 597-601 (2005)). However, the function of p28 is currently not known and work in progress aims at identifying host or viral proteins that are ubiquitinated by p28.
In collaboration with Dr. Mark Slifka, we demonstrated for the first time that some members of the orthopoxvirus family inhibit antigen presentation by MHC class I molecules. In particular, we observed that cowpoxvirus efficiently prevented stimulation of poxvirus-specific cytotoxic T cells and inhibited intracellular exit of MHC class I molecules (Dasgupta J Immunol 178(3), 1654-61 (2007)). Current work aims at elucidating the molecular mechanism and identifying the gene responsible for this immune modulator. 

Früh main

HCMV

KSHV

References