Protective effects of mutant ubiquitin in transgenic mice
D.A. Gray, M. Tsirigotis, J. Brun, M. Tang, M. Zhang, M. Beyers, and J. Woulfe
Ottawa Regional Cancer Centre, 503 Smyth Rd, Ottawa ON K1H 1C4, Canada
The ubiquitin/proteasome pathway (UPP) is responsible for elimination
of damaged and misfolded proteins. In yeast it has been established
that mutant isoforms of ubiquitin unable to participate in ubiquitin
chain assembly exert a dominant negative effect on proteolysis (in the
case of a K48R substitution) or on DNA repair (in the case of a K63R
substitution). To explore the consequences of analogous mutations in
the context of mammalian cells in vivo, we have created transgenic
mouse strains in which wild type or mutant ubiquitin is expressed at
high levels in most tissues. These animals are viable and fertile.
Homozygous individuals from all strains have reached three years of
age, arguing against any dramatic reduction in lifespan. The mice
have been tested for sensitivity to various insults likely to present a
burden of misfolded or aberrant protein. Remarkably, mice expressing
ubiquitin bearing a K48R substitution were found to be resistant to
diverse stressors including the amino acid analogue canavanine, a
neuropathogenic retrovirus encoding a misfolded envelope protein, and a
genetically encoded expanded polyglutamine protein. Such resistance
was not observed in mice expressing K63R mutant ubiquitin.
The apparent paradox presented by our in vivo results clearly arises
from an unexpected consequence of the impaired UPP in the K48R mice.
We are currently investigating several systems in which ubiquitin plays
a role, systems possibly perturbed in these mice. Our present
interests include regulation of transcription, endoplasmic reticulum
associated degradation (ERAD), and endocytosis.
Key words:
ubiquitin proteasome transgenic neurodegeneration
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