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J. Virol., Jun 1997, 4193-4198, Vol 71, No. 6
D Godden-Kent, SJ Talbot, C Boshoff, Y Chang, P Moore, RA Weiss and S Mittnacht
Kaposi's sarcoma-associated herpesvirus (KSHV or human herpesvirus 8) is a
novel gammaherpesvirus implicated in the cause of Kaposi's sarcoma and
certain malignancies of lymphatic origin. One of the candidate genes
possibly involved in promoting tumor development is an open reading frame
(ORF) with sequence similarity to human type D cyclin genes. This
cyclin-like gene, when expressed in tissue culture cells, promotes
phosphorylation and inactivation of the retinoblastoma tumor suppressor
protein and thereby may result in deregulation of cell division control. We
report here the biochemical characterization of this cyclin (KSHV-cyc) and
the kinase activity that it elicits upon expression in tissue culture
cells. We demonstrate that the kinase activity associated with KSHV-cyc is
sensitive to the cdk inhibitor p27 (KIP) and due to activation of cdk6.
However, in contrast to cdk6 activated by cellular type D cyclins, the cdk6
activated by KSHV-cyc is capable of phosphorylating not only the
retinoblastoma protein but also histone H1. This finding implies that
activation by KSHV-cyc alters the substrate preference of this cdk. This
may have important physiological consequences in that the kinase activity
triggered by this viral cyclin may abrogate cell cycle checkpoints in
addition to those targeted by cellular cyclin D-cdk6 kinase.
Copyright © 1997, American Society for Microbiology
The cyclin encoded by Kaposi's sarcoma-associated herpesvirus stimulates cdk6 to phosphorylate the retinoblastoma protein and histone H1
Centre for Molecular and Cell Biology, The Institute of Cancer Research, Chester Beatty Laboratories, London, United Kingdom.
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