PARP1 ADP-ribosylates SMAD3 and SMAD4 in SMAD2/3:SMAD4 heterotrimer. ADP-ribosyl group is attached to glutamic acid residues E50 and E52 of SMAD3 and unknown amino acid residues of SMAD4. ADP-ribose monomer attached to SMAD3 and SMAD4 is subsequently extended to poly (ADP-ribosyl) chains (i.e. PAR chains) by PARP1, which is not shown here. ADP-ribosylation (PARylation) of SMAD3 and SMAD4 by PARP1 inhibits binding of SMAD2/3:SMAD4 heterotrimers to SMAD binding elements (SBEs) in promoters of SMAD-target genes.
Lönn, P, van der Heide, LP, Dahl, M, Hellman, U, Heldin, CH, Moustakas, A
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