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Mol. Cell. Biol., 08 1997, 4859-4869, Vol 17, No. 8
M Ruthardt, U Testa, C Nervi, PF Ferrucci, F Grignani, E Puccetti, F Grignani, C Peschle and PG Pelicci
Fusion proteins involving the retinoic acid receptor alpha (RAR alpha) and
the PML or PLZF nuclear protein are the genetic markers of acute
promyelocytic leukemias (APLs). APLs with the PML-RAR alpha or the PLZF-
RAR alpha fusion protein are phenotypically indistinguishable except that
they differ in their sensitivity to retinoic acid (RA)-induced
differentiation: PML-RAR alpha blasts are sensitive to RA and patients
enter disease remission after RA treatment, while patients with PLZF- RAR
alpha do not. We here report that (i) like PML-RAR alpha expression,
PLZF-RAR alpha expression blocks terminal differentiation of hematopoietic
precursor cell lines (U937 and HL-60) in response to different stimuli
(vitamin D3, transforming growth factor beta1, and dimethyl sulfoxide);
(ii) PML-RAR alpha, but not PLZF-RAR alpha, increases RA sensitivity of
hematopoietic precursor cells and restores RA sensitivity of RA-resistant
hematopoietic cells; (iii) PML-RAR alpha and PLZF-RAR alpha have similar RA
binding affinities; and (iv) PML-RAR alpha enhances the RA response of RA
target genes (those for RAR beta, RAR gamma, and transglutaminase type II
[TGase]) in vivo, while PLZF- RAR alpha expression has either no effect
(RAR beta) or an inhibitory activity (RAR gamma and type II TGase). These
data demonstrate that PML- RAR alpha and PLZF-RAR alpha have similar
(inhibitory) effects on RA- independent differentiation and opposite
(stimulatory or inhibitory) effects on RA-dependent differentiation and
that they behave in vivo as RA-dependent enhancers or inhibitors of
RA-responsive genes, respectively. Their different activities on the RA
signalling pathway might underlie the different responses of PML-RAR alpha
and PLZF-RAR alpha APLs to RA treatment. The PLZF-RAR alpha fusion protein
contains an approximately 120-amino-acid N-terminal motif (called the POZ
domain), which is also found in a variety of zinc finger proteins and a
group of poxvirus proteins and which mediates protein-protein interactions.
Deletion of the PLZF POZ domain partially abrogated the inhibitory effect
of PLZF-RAR alpha on RA-induced differentiation and on RA-mediated type II
TGase up-regulation, suggesting that POZ- mediated protein interactions
might be responsible for the inhibitory transcriptional activities of
PLZF-RAR alpha.
Copyright © 1997, American Society for Microbiology
Opposite effects of the acute promyelocytic leukemia PML-retinoic acid receptor alpha (RAR alpha) and PLZF-RAR alpha fusion proteins on retinoic acid signalling
Istituto di Medicina Interna e Scienze Oncologiche, Policlinico Monteluce, Perugia University, Italy.
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