Kenneth L. Tyler

Professor M.D., Johns Hopkins University

Current Research

Our laboratory uses reoviruses as an experimental model system to understand how discrete viral genes and the proteins they encode determine the capacity of viruses to produce disease in the host (pathogenesis) and injure cells.

A major focus of our laboratory has been the study of virus-induced apoptosis. We have shown that reoviruses can induce apoptosis both in vitro and in vivo, and that reovirus strains differ in this capacity.

We have used reassortant viruses to identify specific viral genes that play a major role in determining the capacity of reoviruses to induce apoptosis. One of the strengths of the reovirus system is the availability of murine models of key human viral diseases including encephalitis, myelitis, myocarditis. We have studied the role of apoptosis in viral pathogenesis in vivo, with a particular emphasis on the CNS and heart. We have found that following infection the sites of tissue injury, viral antigen distribution, and apoptotic cells all co-localize within the same regions within both the mouse brain and heart, indicating that apoptosis is an important mechanism of viral injury to target tissues. We have also shown that manipulation of apoptotic pathways by the use of pharmacologic agents (e.g. inhibitors of caspases, calpain, MAP kinases, neuroprotective agents) as well as in mice with targeted disruptions in key apoptotic proteins, can reduce virus-induced tissue injury in vivo.

We have recently shown that reoviruses selectively activate specific mitogen activated protein kinase (MAPK) pathways and their associated transcription factors including c-Jun in infected cells, and that inhibition of this activation can inhibit apoptosis. Viral infection also results in a complex regulation of NF-kappaB, with apoptosis inducing viral strains initially activating and then inhibiting NF-kappaB activation. These results suggest that both induction of pro-apoptotic and inhibition of the expression of anti-apoptotic genes may play a critical role in reovirus apoptosis. We are currently using genomic and other approaches to identify the specific cellular genes and proteins involved.
We are using both primary neuronal and cardiac cultures and continuous lines to investigate cellular mechanisms and pathways of apoptosis. The availability of both primary culture systems and in vivo models of infection, allows results obtained in cell culture to be tested for their applicability to pathogenesis in vivo. Regardless of cell type, reovirus-induced apoptosis involves members of the TNF superfamily of cell death receptors. In epithelial and cancer cell lines death receptors 4 and 5 (DR4, DR5) and their apoptosis-inducing ligand TRAIL appear to play a critical role in the initiation of reovirus-induced apoptosis. In neuronal cells the Fas/FasL system plays an analogous role. Death-receptor activation results in activation of the death-receptor associated initiator caspase, caspase 8. Caspase 8 activation cleaves the Bcl-2 family protein Bid, which in turn translocates to the mitochondria and promotes cystosolic release of Smac/DIABLO and other pro-apoptotic mitochondrial factors. These factors in turn potentiate reovirus apoptosis through mechanisms including their inhibition of cellular inhibitor of apoptosis proteins (IAPs).

Studies are currently underway to analyze: (1) the cellular mechanisms involved in apoptosis induction including the role of MAP kinase signal transduction pathways, JAK/STAT and TGF-beta signaling pathways, the role of reactive oxygen species and of c-JUN, NF-kappa B and other transcription factors, (2) the mechanisms by which mitochondrial apoptotic events are triggered, including the role of Bcl-2 family proteins and how they are regulated by MAPK activation pathways, (3) the precise genes whose regulation is altered during apoptosis, and (4) the significance of apoptotic events on pathogenesis in vivo, and the effects on viral infection and injury of manipulating apoptotic pathways.


More about the Tyler Lab

Recent Publications

Click here For An Updated List Of Dr. Tyler's Publications

Zimmermann AK, Loucks FA, Schroeder EK, Bouchard RJ, Tyler KL, Linseman DA. Glutathione binding to the Bcl-2 homology-3 domain groove: A molecular basis for Bcl-2 antioxidant function at mitochondria. J Biol Chem. 2007 Aug 9; [Epub ahead of print]PMID: 17690097

Beckham JD, Goody RJ, Clarke P, Bonny C, Tyler KL. Novel strategy for treatment of viral central nervous system infection by using a cell-permeating inhibitor of c-Jun N-terminal kinase. J Virol. 2007 Jul;81(13):6984-92.

Clarke P, Tyler KL. Down-regulation of cFLIP following reovirus infection sensitizes human ovarian
cancer cells to TRAIL-induced apoptosis. Apoptosis. 2007 Jan;12(1):211-23.

Goody RJ, Hoyt CC, Tyler KL. Reovirus infection of the CNS enhances iNOS expression in areas of virus-induced injury. Exp Neurol. 2005 Oct;195(2):379-90.

Clarke P, Debiasi RL, Meintzer SM, Robinson BA, Tyler KL. Inhibition of NF-kappa B activity and cFLIP expression contribute to viral-induced apoptosis. Apoptosis. 2005 May;10(3):513-24.

Clarke P, Debiasi RL, Goody R, Hoyt CC, Richardson-Burns S, Tyler KL. Mechanisms of reovirus-induced cell death and tissue injury: role of apoptosis and virus-induced perturbation of host-cell signaling and transcription factor activation. Viral Immunol. 2005;18(1):89-115.

Richardson-Burns SM, Tyler KL. Minocycline delays disease onset and mortality in reovirus encephalitis. Exp Neurol. 2005 Apr;192(2):331-9.

Hoyt CC, Richardson-Burns SM, Goody RJ, Robinson BA, Debiasi RL, Tyler KL. Nonstructural protein sigma1s is a determinant of reovirus virulence and influences the kinetics and severity of apoptosis induction in the heart and central nervous system. J Virol. 2005 Mar;79(5):2743-53.

Clarke P, Meintzer SM, Wang Y, Moffitt LA, Richardson-Burns SM, Johnson GL, Tyler KL.
JNK regulates the release of proapoptotic mitochondrial factors in reovirus-infected cells. J Virol. 2004 Dec;78(23):13132-8.

DeBiasi RL, Robinson BA, Sherry B, Bouchard R, Brown RD, Rizeq M, Long C, Tyler KL.
Caspase inhibition protects against reovirus-induced myocardial injury in vitro and in vivo. J Virol. 2004 Oct;78(20):11040-50.