Carcinogenesis, Vol 19, 1223-1230, Copyright © 1998 by Oxford University Press
CM Benedict, W Pan, SE Loy and GA Clawson
We have been developing triple ribozyme (TRz) constructs which consist of
two cis-acting ribozymes flanking an internal trans-acting ribozyme, which
is targeted to a cellular RNA. Actions of the two cis-acting ribozymes
efficiently liberate the internal ribozyme with minimal non- specific
flanking sequences. The liberated internal targeted ribozyme shows
substantially greater catalytic activity than TRz preparations, constructs
which cannot undergo self-liberation or than single ribozymes with flanking
vector sequences. Here we construct a TRz which was targeted to
retinoblastoma gene (Rb) mRNA, which cleaved Rb target RNA in vitro as
expected. A number of tetracycline-regulatable clones stably transfected
with the Rb-targeted TRz were developed and analyzed. The internal targeted
ribozymes were efficiently liberated in vivo and the stably transfected
clones showed varied reductions in Rb mRNA, which were contingent upon
ribozyme expression and catalytic activity. The two clones showing major
reductions in Rb mRNA (and pRb) levels (>70% reduction) showed abnormal
morphology, loss of contact inhibition and the ability to grow in soft
agar, as well as altered compartmentation of repetitive B2 transcripts, a
phenomenon previously associated with immortalization and/or
transformation. TRz constructs coupled with tissue-specific promoters
should allow development of in vivo models in which Rb function is markedly
reduced in a tissue- specific manner.
ARTICLES
Triple ribozyme-mediated down-regulation of the retinoblastoma gene
Department of Pathology, M.S. Hershey Medical Center, Pennsylvania State University, Hershey 17033, USA.
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