Monomer; in the absence of TGF-beta. Homooligomer; in the presence of TGF-beta. Heterotrimer; forms a heterotrimer in the presence of TGF-beta consisting of two molecules of C-terminally phosphorylated
SMAD2 or
SMAD3 and one of
SMAD4 to form the transcriptionally active
SMAD2/
SMAD3-
SMAD4 complex. Interacts with
TGFBR1. Part of a complex consisting of AIP1,
ACVR2A,
ACVR1B and
SMAD3. Interacts with AIP1,
TGFB1I1, TTRAP,
FOXL2,
PML,
PRDM16,
HGS,
WWP1 and
SNW1. Interacts (via MH2 domain) with
CITED2 (via C-terminus). Interacts with
NEDD4L; the interaction requires TGF-beta stimulation. Interacts (via the MH2 domain) with
ZFYVE9. Interacts with
HDAC1, TGIF and
TGIF2,
RUNX3,
CREBBP,
SKOR1,
SKOR2, SNON,
ATF2,
SMURF2 and
TGFB1I1. Interacts with
DACH1; the interaction inhibits the TGF-beta signaling. Forms a complex with
SMAD2 and
TRIM33 upon addition of TGF-beta. Found in a complex with
SMAD3,
RAN and
XPO4. Interacts in the complex directly with
XPO4. Interacts (via the MH2 domain) with
LEMD3; the interaction represses
SMAD3 transcriptional activity through preventing the formation of the heteromeric complex with
SMAD4 and translocation to the nucleus. Interacts with
RBPMS. Interacts (via MH2 domain) with
MECOM. Interacts with
WWTR1 (via its coiled-coil domain). Interacts (via the linker region) with
EP300 (C-terminal); the interaction promotes
SMAD3 acetylation and is enhanced by TGF-beta phosphorylation in the C-terminal of
SMAD3. This interaction can be blocked by competitive binding of adenovirus oncoprotein E1A to the same C-terminal site on
EP300, which then results in partially inhibited
SMAD3/
SMAD4 transcriptional activity. Interacts with
SKI; the interaction represses
SMAD3 transcriptional activity. Component of the multimeric complex
SMAD3/
SMAD4/
JUN/
FOS which forms at the AP1 promoter site; required for synergistic transcriptional activity in response to TGF-beta. Interacts (via an N-terminal domain) with
JUN (via its basic DNA binding and leucine zipper domains); this interaction is essential for DNA binding and cooperative transcriptional activity in response to TGF-beta. Interacts with
PPM1A; the interaction dephosphorylates
SMAD3 in the C-terminal SXS motif leading to disruption of the
SMAD2/3-
SMAD4 complex, nuclear export and termination of TGF-beta signaling. Interacts (dephosphorylated form via the MH1 and MH2 domains) with
RANBP3 (via its C-terminal R domain); the interaction results in the export of dephosphorylated
SMAD3 out of the nucleus and termination of the TGF-beta signaling. Interacts with
MEN1. Interacts with IL1F7. Interaction with
CSNK1G2. Interacts with
PDPK1 (via PH domain). Interacts with
DAB2; the interactions are enhanced upon TGF-beta stimulation. Interacts with
USP15. Interacts with
PPP5C; the interaction decreases
SMAD3 phosphorylation and protein levels. Interacts with
LDLRAD4 (via the SMAD interaction motif). Interacts with
PMEPA1. Interacts with
ZC3H3 (By similarity). Interacts with
ZNF451 (PubMed:24324267). Identified in a complex that contains at least
ZNF451,
SMAD2,
SMAD3 and
SMAD4 (PubMed:24324267). Interacts with
ZFHX3. Interacts weakly with
ZNF8 (PubMed:12370310). Interacts (when phosphorylated) with
RNF111;
RNF111 acts as an enhancer of the transcriptional responses by mediating ubiquitination and degradation of
SMAD3 inhibitors (By similarity). Interacts with
STUB1,
HSPA1A,
HSPA1B,
HSP90AA1 and
HSP90AB1 (PubMed:24613385).
UniProt