This thesis concerns gene 176R from camelpox virus (CMLV) that encodes a protein
known as viral schlafen (v-slfn). v-slfn has an N-terminal domain related to the p26
protein from baculovirus and a C-terminal domain related to mammalian schlafen
proteins. A full length v-slfn is expressed by all sequenced orthopoxviruses except
vaccinia virus (VACV) and variola virus. The baculovirus p26 proteins are poorly
characterised, with no known function. In contrast, murine schlafen (m-slfn) proteins
are upregulated in response to infection and the promoter for m-slfn2 has NF-κB and
AP-1 binding sites. The prototypic slfn, m-slfn1, halts cellular proliferation by
inhibition of cyclin D1 expression in vitro and both m-slfn1 and m-slfn8 reduce
thymocyte proliferation in vivo.
v-slfn is a predominantly cytoplasmic protein of 57 kDa that is expressed both early
and late during CMLV infection. Expression of v-slfn reverses the growth arrest
resulting from m-slfn1 expression, and this is a result of a reversal of the inhibition of
cyclin D1 expression. This effect can be seen following overexpression of various
transcription factors that upregulate cyclin D1 expression.
Recombinant VACV expressing enhanced levels of v-slfn replicated and spread at a
comparable rate to control viruses in vitro, but was less virulent than controls in the
intranasal model of infection in vivo. A group of viruses based on VACV WR were
constructed, which lack the gene fragments (B2R and B3R) corresponding to CMLV
176R. The undisrupted sequence for 176R was also re-inserted at this locus,
resulting in a virus that expresses v-slfn from its natural promoter. In vitro
characterisation showed no differences in replication or spread when compared to
controls.
Thus, v-slfn is an orthologue of mammalian slfn proteins, and may exert its effect by
reversing their inhibition of cellular proliferation
