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Mol. Cell. Biol., 01 1995, 35-44, Vol 15, No. 1
S Vagner, MC Gensac, A Maret, F Bayard, F Amalric, H Prats and AC Prats
Alternative initiations of translation of the human fibroblast growth
factor 2 (FGF-2) mRNA, at three CUG start codons and one AUG start codon,
result in the synthesis of four isoforms of FGF-2. This process has
important consequences on the fate of FGF-2: the CUG-initiated products are
nuclear and their constitutive expression is able to induce cell
immortalization, whereas the AUG-initiated product, mostly cytoplasmic, can
generate cell transformation. Thus, the different isoforms probably have
distinct targets in the cell. We show here that translation initiation of
the FGF-2 mRNA breaks the rule of the cap- dependent ribosome scanning
mechanism. First, translation of the FGF-2 mRNA was shown to be cap
independent in vitro. This cap-independent translation required a sequence
located between nucleotides (nt) 192 and 256 from the 5' end of the
318-nt-long 5' untranslated region. Second, expression of bicistronic
vectors in COS-7 cells indicated that the FGF-2 mRNA is translated through
a process of internal ribosome entry mediated by the mRNA leader sequence.
By introducing additional AUG codons into the RNA leader sequence, we
localized an internal ribosome entry site to between nt 154 and 318 of the
5' untranslated region, just upstream of the first CUG. The presence of an
internal ribosome entry site in the FGF-2 mRNA suggests that the process of
internal translation initiation, by controlling the expression of a growth
factor, could have a crucial role in the control of cell proliferation and
differentiation.
Copyright © 1995, American Society for Microbiology
Alternative translation of human fibroblast growth factor 2 mRNA occurs by internal entry of ribosomes
INSERM U397, Endocrinologie et Communication Cellulaire, Institut Louis Bugnard, Centre Hospitalier Universitaire de Rangueil, Toulouse, France.
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