STRING 9.05 
SMAD4 [ENSP00000341551]
SMAD family member 4; Common mediator of signal transduction by TGF-beta (transforming growth factor) superfamily; SMAD4 is the common SMAD (co-SMAD). Promotes binding of the SMAD2/SMAD4/FAST-1 complex to DNA and provides an activation function required for SMAD1 or SMAD2 to stimulate transcription. May act as a tumor suppressor
SMAD2 [ENSP00000262160]
SMAD family member 2; Transcriptional modulator activated by TGF-beta and activin type 1 receptor kinase. SMAD2 is a receptor-regulated SMAD (R-SMAD). May act as a tumor suppressor in colorectal carcinoma
Evidence suggesting a functional link:
Neighborhood in the Genome:  
none / insignificant.
Gene Fusions:  
none / insignificant.
Cooccurence Across Genomes:  
none / insignificant.
Co-Expression:   yes (score 0.264).  
Experimental/Biochemical Data:   yes (score 0.999). In addition, putative homologs were found interacting in other species (score 0.108).  
Association in Curated Databases:   yes (score 0.900).  
Co-Mentioned in PubMed Abstracts:   yes (score 0.976).  
Combined Score:
Note: the two proteins have some sequence similarity (300.7 bits over 423 amino acids. click here to see the alignment).
Evidence for specific actions:
Expression:yes (score: 0.800)  
Activation:yes (score: 0.800)  
Binding:yes (score: 0.999)