SMADs are a novel set of mammalian proteins that act downstream of TGF-beta family ligands. These proteins can be categorized into three distinct functional sets, receptor-activated SMADs (SMADs 1,2,3,5, and 8), the common mediator SMAD (SMAD 4), and inhibitory SMADs (SMADs 6 and 7). SMAD proteins are thought to play a role in vertebrate development and tumorigenesis.

One of the research tools our NIH inventors have prepared is the Smad3-null mice model, created by disrupting exon 8 on the Smad3 gene. Symptomatic mice exhibit leukocytosis, with massive inflammation and pyogenous abscess formation adjacent to mucosal surfaces. Smad3 plays an important role in mediating TGF-beta signals in T lymphocytes and in neutrophils, and demonstrate that Smad3 deficiency results in immune dysregulation and susceptibility to opportunistic infection, ultimately leading to the lethality of the mice between 1 and 8 months. TGF-beta signals also play a role in cancer formation in multiple organs and tissues. Smad3-null mice could be used to clone downstream target genes for TGF-beta signals, which may be used in gene therapy and chemoprevention studies.

Smad4-null mice die around embryonic day 6.5, so the inventors prepared the SMAD4-conditional mice model, created by a Smad4 conditional knockout allele at exon 8 using Cre-mediated recombination. PCR analysis determined Cre-mediated recombination in the pancreas but not in a number of other organs, indicating that the Smad4 conditional allele can be recombined to delete exon 8 in a tissue-specific fashion. This knockout mouse could be used to test the function of TGF-beta/Smad4 signals at all stages of mouse development. Interestingly, mutation of human Smad4 has been found in approximately half of all pancreatic cancers, 30% of colon cancers, and about 10% in other cancers. The Smad4-conditional mice could be used to study pathways that are involved in formation of these tumors or to clone downstream target genes that may be used in gene therapy and chemoprevention studies.