Endosomal adaptor proteins APPL1 and APPL2 are novel activators of beta-catenin/TCF-mediated transcription.
Canonical Wnt signaling regulates many aspects of cellular physiology and tissue homeostasis during development and in adult organisms. In molecular terms, stimulation by Wnt ligands leads to the stabilization of beta-catenin, its translocation to the nucleus, and stimulation of TCF (T-cell factor)-dependent transcription of target genes. This process is controlled at various stages by a number of regulatory proteins, including transcriptional activators and repressors. Here we demonstrate that the endosomal proteins APPL1 and APPL2 are novel activators of beta-catenin/TCF-mediated transcription. APPL proteins are multifunctional adaptors and effectors of the small GTPase Rab5, which localize to a subpopulation of early endosomes but are also capable of nucleocytoplasmic shuttling. Overexpression of APPL1 or APPL2 protein stimulates the activity of beta-catenin/TCF-dependent reporter construct, whereas silencing of APPL1 reduces it. Both APPL proteins interact directly with Reptin, a transcriptional repressor binding to beta-catenin and HDAC1 (histone deacetylase 1), and this interaction was mapped to the pleckstrin homology domain of APPL1. Moreover, APPL proteins are present in an endogenous complex containing Reptin, beta-catenin, HDAC1, and HDAC2. Overexpression of either APPL protein relieves Reptin-dependent transcriptional repression and correlates with the reduced amounts of HDACs and beta-catenin associated with Reptin as well as with the lower levels of Reptin and HDAC1 on the promoters of beta-catenin target genes. We propose that APPL proteins exert their stimulatory effects on beta-catenin/TCF-dependent transcription by decreasing the activity of a Reptin-containing repressive complex.
Laboratory of Cell Biology, International Institute of Molecular and Cell Biology, Ks. Trojdena 4, 02-109 Warsaw, Poland.
Sajid
S
Rashid
Iwona
I
Pilecka
Anna
A
Torun
Marta
M
Olchowik
Beata
B
Bielinska
Marta
M
Miaczynska
D000074183:ATPases Associated with Diverse Cellular Activities; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology; D006367:HeLa Cells; D006655:Histone Deacetylases / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007668:Kidney / Q000166:cytology; D008156:Luciferases / Q000235:genetics; D051379:Mice; D046912:Multiprotein Complexes / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000502:physiology; D017434:Protein Structure, Tertiary; D015398:Signal Transduction / Q000502:physiology; D051820:TCF Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation / Q000502:physiology*; D014162:Transfection; D051153:Wnt Proteins / Q000378:metabolism; D051176:beta Catenin / Q000378:metabolism*
C464801:APPL1 protein, human; C528555:APPL2 protein, human; D048868:Adaptor Proteins, Signal Transducing; C495270:CTNNB1 protein, human; D002352:Carrier Proteins; D046912:Multiprotein Complexes; D051820:TCF Transcription Factors; D051153:Wnt Proteins; D051176:beta Catenin; D008156:Luciferases; D006655:Histone Deacetylases; D000074183:ATPases Associated with Diverse Cellular Activities; D004265:DNA Helicases; C122079:RUVBL2 protein, human