Cell surface interactions of Coxsackie A9 virus

An understanding of how viruses interact with their receptors is vital as this step is a major determinant of host susceptibility and disease. Coxsackievirus A9 (CAV9), an enterovirus, harbours an integrin- recognition motif, RGD (Arg-Gly-Asp), in the capsid protein VP1 and although modes of transmission and pathogenesis are still largely unknown, this motif is believed to be primarily responsible for integrins αvβ6 and αvβ3 binding. The conservation of the RGD +1 position in CAV9 and other picornaviruses showed evidence that this is related to viral tropism and infectiousness of the virus. CAV9 has also been reported to interact with the heparan sulphate/heparin class of proteoglycans (HSPG). This thesis describes work designed to improve our understanding of the involvement of a) the RGD motif and more specifically the RGDX position in CAV9 infection, using a large panel of different RGDX variants and a number of cell lines not previously used in CAV9 research b) the significance of possible interactions between CAV9 and HSPG in infection. Several CAV9 variants were tested in a panel of 8 different cell lines. Infection in each cell line was observed to follow either an RGD- dependant or RGD- independent pathway, although the results did not fully correlate with the receptor expression found on the cell lines used. The RGDX position was found to be critical for efficient infection in cells when an RGD- dependent pathway is used. To understand which integrin is likely to be involved in entry, into one of the RGD-dependent cell lines, A549, blocking antibodies against αvβ3 and αvβ6 were used. Neither antibody gave full protection against CAV9, as has been reported previously, suggesting that other integrins might also be used. Two new HSPG-binding CAV9 mutants were discovered, showing that binding to HSPG can be achieved by several mechanisms. Binding to HSPG was found to be significant in some cells, but not others, again illustrating the complexity of interactions between CAV9 and the cell surface. The results obtained have greatly improved our understanding of how CAV9 infects cells. This will be useful in the design of antivirus drugs and also gives a framework for the modification of CAV9 or other RGD containing picornaviruses for specific targeting of cancer cells for oncolytic therapy.