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Genes in the SMAD gene family provide instructions for producing proteins that help regulate the activity of particular genes as well as cell growth and division (proliferation). The proteins carry out these functions as part of the transforming growth factor beta (TGF-β) pathway, which transmits signals from the outside of the cell to the nucleus. This type of signaling pathway allows the environment outside the cell to affect how the cell produces other proteins.
The signaling process begins when a protein called TGF-β attaches (binds) to a receptor on the surface of the cell, which then turns on (activates) a group of SMAD proteins (called receptor-regulated SMADs or R-SMADs). The R-SMADs include the SMAD1, SMAD2, SMAD3, SMAD5, and SMAD8 proteins. These R-SMADs then bind together in multiple protein groups (or complexes) with another SMAD protein, SMAD4, also called the common mediator SMAD (or Co-SMAD). Once the SMAD protein complexes form, they are transported to the nucleus. In the nucleus, the SMAD complexes bind to specific areas of DNA, where they control the activity of particular genes and regulate cell proliferation.
When the signaling pathway needs to be turned off, two SMAD proteins, SMAD6 and SMAD7 (known as the inhibitory SMADs or I-SMADs), inactivate the receptors for the TFG-β protein on the cell surface. The I-SMADs are also thought to interfere with the formation of SMAD-SMAD4 complexes and interfere with the interaction between the SMAD complex and DNA in the cell nucleus.
The HUGO Gene Nomenclature Committee (HGNC) provides an index of gene families (http://www.genenames.org/cgi-bin/genefamilies/) and their member genes.
Genetics Home Reference summarizes the normal function and health implications of these members of the SMAD gene family: SMAD3 and SMAD4.
Genetics Home Reference includes these conditions related to genes in the SMAD gene family:
You may find the following resources about the SMAD gene family helpful.
cell ; cell nucleus ; cell proliferation ; DNA ; domain ; gene ; growth factor ; homologs ; ligand ; nucleus ; proliferation ; protein ; receptor ; transcription ; transcription factor ; tumor
You may find definitions for these and many other terms in the Genetics Home Reference Glossary.
These sources were used to develop the Genetics Home Reference summary for the SMAD gene family.
The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.