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Mol. Cell. Biol., Jun 1995, 3138-3146, Vol 15, No. 6
GN Barber, M Wambach, S Thompson, R Jagus and MG Katze
Recently we reported that introduction of catalytically inactive PKR
molecules into NIH 3T3 cells causes malignant transformation and the
development of tumors in nude mice. We have proposed that PKR may be a
tumor suppressor gene possibly because of its translational inhibitory
properties. We have now designed and characterized a number of PKR mutants
encoding proteins that retain their catalytic competence but are mutated in
their regulatory double-stranded RNA (dsRNA) binding domains (RBDs). RNA
binding analysis revealed that PKR proteins either lacking or with point
mutations in the first RBD (RBD-1) bound negligible amounts of dsRNA
activator or adenovirus VAI RNA inhibitor. Despite the lack of binding,
such variants remained functionally competent but were much less active
than wild-type PKR. PKR variants completely lacking RBD-1 were largely
unresponsive to dsRNA in activation assays but could be activated by
heparin. To complement these studies, we evaluated the effects of point
mutations in RBD-1 or the removal of either RBD-1 or RBD-2 on the
proliferation rate of mouse 3T3 cells. We were unsuccessful at isolating
stably transformed cells expressing RBD-1 point mutants or RBD-2-minus
mutants. In contrast, NIH 3T3 cells, which constitutively expressed PKR
proteins that lacked RBD- 1, were selected. These cells displayed a
transformed phenotype and caused tumors after inoculation in nude mice.
Further, levels of endogenous eIF-2 alpha phosphorylation in RBD-1-minus
cell lines were reduced, suggesting that such mutants act in a dominant
negative manner to inhibit the function of endogenous PKR.(ABSTRACT
TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
Mutants of the RNA-dependent protein kinase (PKR) lacking double- stranded RNA binding domain I can act as transdominant inhibitors and induce malignant transformation
Department of Microbiology, School of Medicine, University of Washington, Seattle 98195, USA.
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