title: Role of the translational repressor 4E-BP1 in the regulation of p21(Waf1/Cip1) expression by retinoids.
abstract: The mechanisms by which retinoids regulate initiation of mRNA translation for proteins that mediate their biological effects are not known. We have previously shown that all-trans-retinoic acid (ATRA) induces mTOR-mediated activation of the p70 S6 kinase, suggesting the existence of a mechanism by which retinoids may regulate mRNA translation. We now demonstrate that treatment of acute promyelocytic leukemia (APL)-derived NB4 cells with ATRA results in dissociation of the translational repressor 4E-BP1 from the eukaryotic initiation factor eIF4E, and subsequent formation of eIF4G-eIF4E complexes. We also show that siRNA-mediated inhibition of 4E-BP1 expression enhances ATRA-dependent upregulation of p21(Waf1/Cip1), a protein that plays a key role in the induction of retinoid-dependent responses. Our data also establish that ATRA- or cis-RA-dependent p21(Waf1/Cip1) protein expression is enhanced in mouse embryonic fibroblasts with targeted disruption of the 4e-bp1 gene, in the absence of any effects on the transcriptional regulation of the p21(Waf1/Cip1) gene. Moreover, generation of ATRA- or cis-retinoic acid (cis-RA)-antiproliferative responses is enhanced in 4E-BP1 knockout cells. Altogether, these findings strongly suggest a key regulatory role for the translational repressor 4E-BP1 in the generation of retinoid-dependent functional responses.
authors.affiliation: Robert H. Lurie Comprehensive Cancer Center and Division of Hematology-Oncology, Northwestern University Medical School and Jesse Brown VA Medical Center, 303 East Superior, Chicago, IL, USA.
authors.forename: Padma
authors.initials: P
authors.lastname: Kannan-Thulasiraman
authors.forename: Blazej
authors.initials: B
authors.lastname: Dolniak
authors.forename: Surinder
authors.initials: S
authors.lastname: Kaur
authors.forename: Antonella
authors.initials: A
authors.lastname: Sassano
authors.forename: Dhananjaya V
authors.initials: DV
authors.lastname: Kalvakolanu
authors.forename: Nissim
authors.initials: N
authors.lastname: Hay
authors.forename: Leonidas C
authors.initials: LC
authors.lastname: Platanias
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000502:physiology*; D000818:Animals; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000096:biosynthesis*; D039561:Eukaryotic Initiation Factor-4E / Q000378:metabolism; D015973:Gene Expression Regulation, Leukemic / Q000187:drug effects; D006801:Humans; D015473:Leukemia, Promyelocytic, Acute; D051379:Mice; D018345:Mice, Knockout; D010750:Phosphoproteins / Q000502:physiology*; D014212:Tretinoin / Q000494:pharmacology*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; C087000:EIF4EBP1 protein, human; D039561:Eukaryotic Initiation Factor-4E; D010750:Phosphoproteins; D014212:Tretinoin