The role of protein kinase B/Akt in pathogenesis of coxsackievirus B3 myocarditis

• Main Author: Esfandiarei, Mitra
• Language: English
• Published: 2010
• Online Access: http://hdl.handle.net/2429/18256

Viral myocarditis is a major cause of sudden cardiac death in children and young adults. Among viruses, coxsackievirus B3 (CVB3), a small non-enveloped single-stranded RNA enterovirus in the Picornaviridae family, is the most prominent infective agent for myocarditis, causing myocardial injury that, at times leads to end-stage dilated cardiomyopathy. Recently, more consideration has been devoted to the role of signalling pathways in the pathogenesis of enteroviral myocarditis as a route for identifying new potential therapeutic targets. The role of signalling proteins including the extracellular signal-regulated kinase (ERKI/2 MAPK), stress-activated protein kinase c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (p38 MAPK) during CVB3 infection has been comprehensively studied by us and others. However, the potential regulatory function of other kinases such as the survival signalling molecule protein kinase B/Akt remains elusive. In the present study, we have investigated the potential regulatory function of the PI3K/Akt pathway in progression of CVB3-induced myocarditis. Our findings demonstrate that CVB3 enhances Akt phosphorylation through a phosphatidylinositol-3 kinase (PI3K)-dependent mechanism. Inhibition of Akt significantly suppresses viral RNA expression and progeny release while increasing apoptosis of infected cells. Interestingly, inhibition of apoptotic events does not reverse the inhibitory effect of Akt inhibition on virus life replication, suggesting that the observed regulatory role of Akt is not dependent on the anti-apoptotic function of this protein kinase. Virus-induced Akt phosphorylation in mouse cardiomyocytes and HeLa cells is also mediated through the integrin-linked kinase (ILK). Inhibition of ILK significantly reduces viral replication and progeny release and improves viability of infected cardiomyocytes. Over-expression of a constitutively active form of Akt protein within virus-infected cells has provided evidence that the protective effect of ILK inhibition is dependent on associated down-regulation of virus-induced Akt activation. In the present study, we also investigated the role of the transcription factor nuclear factor kappa-B (NFkB) as a candidate downstream mediator of signals through the PI3K/Akt cascade in regulating CVB3 replication and virus-mediated cytopathic effects. Our findings suggest that activation of NFkB is an early event with an anti-apoptotic function. Inhibition of PI3K and Erk1/2 pathways significantly blocks virus-induced NFkB activation, proposing a major role for these kinases in regulation of host transcriptional events during CVB3 infection. Most importantly, short-term treatment of infected cells with tumor necrosis factor-α [i.e. tumour necrosis factor-α] (TNF-α), a potent activator of NFkB, rescues infected cells, apparently through increasing the DNA-binding activity of NFkB. Long-term treatment with TNF-α, however, has been shown to be detrimental to the host cell, emphasizing the importance of the delicate balance between deleterious and protective effects of NFkB activation. In summary, this dissertation presents the first report on the regulatory role of the PI3K/Akt pathway during the course of enteroviral infection, provides valuable information on molecular mechanisms underlying CVB3 pathogenesis, and offers new insights to our effort in establishing an effective therapeutic approach to alleviate enteroviral myocarditis. === Medicine, Faculty of === Pathology and Laboratory Medicine, Department of === Graduate