Mothers against decapentaplegic homolog 7 or SMAD7 is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

that in humans is encoded by the ''SMAD7''

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

. SMAD7 is a protein that, as its name describes, is a homolog of the

Drosophila ''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species ...

gene: "

Mothers against decapentaplegic Mothers against decapentaplegic is a protein from the SMAD family that was discovered in ''Drosophila''. During ''Drosophila'' research, it was found that a mutation in the gene in the mother repressed the gene decapentaplegic in the embryo. The ...

". It belongs to the SMAD family of proteins, which belong to the

TGFβ Transforming growth factor beta (TGF-β) is a multifunctional cytokine belonging to the transforming growth factor superfamily that includes three different mammalian isoforms (TGF-β 1 to 3, HGNC symbols TGFB1, TGFB2, TGFB3) and many other sig ...

superfamily of ligands. Like many other TGFβ family members, SMAD7 is involved in

cell signalling In biology, cell signaling (cell signalling in British English) or cell communication is the ability of a cell to receive, process, and transmit signals with its environment and with itself. Cell signaling is a fundamental property of all cellula ...

. It is a TGFβ type 1

receptor antagonist A receptor antagonist is a type of receptor ligand or drug that blocks or dampens a biological response by binding to and blocking a receptor rather than activating it like an agonist. Antagonist drugs interfere in the natural operation of rece ...

. It blocks TGFβ1 and activin associating with the receptor, blocking access to

SMAD2 Mothers against decapentaplegic homolog 2 also known as SMAD family member 2 or SMAD2 is a protein that in humans is encoded by the ''SMAD2'' gene. MAD homolog 2 belongs to the SMAD, a family of proteins similar to the gene products of the ''Dros ...

. It is an inhibitory SMAD (

I-SMAD I-SMAD or Inhibitor SMAD is a subclass of SMADs that are involved in the modulation of transforming growth factor beta ligands. This class includes SMAD6 and SMAD7. They compete with SMAD4 and consequently regulate the transcription of its gene ...

) and is enhanced by

SMURF2 E3 ubiquitin-protein ligase SMURF2 is an enzyme that in humans is encoded by the ''SMURF2'' gene which is located at chromosome 17q23.3-q24.1. Interactions SMURF2 has been shown to interact with: * Mothers against decapentaplegic homolog 1, * ...

. Smad7 enhances muscle differentiation.

Structure

Smad proteins contain two conserved domains. The Mad Homology domain 1 (MH1 domain) is at the

N-terminal The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide, referring to the free amine group (-NH2) located at the end of a polypeptide. Within a peptide, the ami ...

and the Mad Homology domain 2 (MH2 domain) is at the

C-terminal The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal tail, C-terminal end, or COOH-terminus) is the end of an amino acid chain (protein or polypeptide), terminated by a free carboxyl group (-COOH). When the protein is ...

. Between them there is a linker region which is full of regulatory sites. The MH1 domain has DNA binding activity while the MH2 domain has transcriptional activity. The linker region contains important regulatory peptide motifs including potential

phosphorylation In chemistry, phosphorylation is the attachment of a phosphate group to a molecule or an ion. This process and its inverse, dephosphorylation, are common in biology and could be driven by natural selection. Text was copied from this source, wh ...

sites for mitogen-activated protein kinases(

MAPK A mitogen-activated protein kinase (MAPK or MAP kinase) is a type of protein kinase that is specific to the amino acids serine and threonine (i.e., a serine/threonine-specific protein kinase). MAPKs are involved in directing cellular responses to ...

s), Erk-family MAP kinases, the Ca2+ /calmodulin-dependent protein kinase II (CamKII) and

protein kinase C In cell biology, Protein kinase C, commonly abbreviated to PKC (EC 2.7.11.13), is a family of protein kinase enzymes that are involved in controlling the function of other proteins through the phosphorylation of hydroxyl groups of serine and t ...

(PKC). Smad7 does not have the MH1 domain. A proline-tyrosine (PY) motif presents at its linker region enables its interaction with the WW domains of the E3

ubiquitin Ubiquitin is a small (8.6 kDa) regulatory protein found in most tissues of eukaryotic organisms, i.e., it is found ''ubiquitously''. It was discovered in 1975 by Gideon Goldstein and further characterized throughout the late 1970s and 1980s. Fo ...

ligase, the Smad ubiquitination-related factors (Smurf2). It resides predominantly in the nucleus at basal state and translocates to the

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. The ...

upon TGF-β stimulation.

Function

SMAD7 inhibits TGF-β signaling by preventing formation of Smad2/

Smad4 SMAD4, also called SMAD family member 4, Mothers against decapentaplegic homolog 4, or DPC4 (Deleted in Pancreatic Cancer-4) is a highly conserved protein present in all metazoans. It belongs to the SMAD family of transcription factor proteins, ...

complexes which initiate the TGF-β signaling. It interacts with activated TGF-β type I receptor therefore block the association, phosphorylation and activation of Smad2. By occupying type I receptors for Activin and

bone morphogenetic protein Bone morphogenetic proteins (BMPs) are a group of growth factors also known as cytokines and as metabologens. Originally discovered by their ability to induce the formation of bone and cartilage, BMPs are now considered to constitute a group of piv ...

(BMP), it also plays a role in

negative feedback Negative feedback (or balancing feedback) occurs when some function (Mathematics), function of the output of a system, process, or mechanism is feedback, fed back in a manner that tends to reduce the fluctuations in the output, whether caused by ...

of these pathways. Upon TGF- β treatment, Smad7 binds to discrete regions of Pellino-1 via distinct regions of the Smad MH2 domains. The interaction blocks the formation of the

IRAK1 Interleukin-1 receptor-associated kinase 1 (IRAK-1) is an enzyme in humans encoded by the ''IRAK1'' gene. IRAK-1 plays an important role in the regulation of the expression of inflammatory genes by immune cells, such as monocytes and macrophages, ...

-mediated

IL-1R Interleukin-1 receptor (IL-1R) is a cytokine receptor which binds interleukin 1 The Interleukin-1 family (IL-1 family) is a group of 11 cytokines that plays a central role in the regulation of immune and inflammatory responses to infections ...

/ TLR signaling complex therefore abrogates NF-κB activity, which subsequently causes reduced expression of pro- inflammatory genes. While Smad7 is induced by TGF-β, it is also induced by other stimuli, such as

epidermal growth factor Epidermal growth factor (EGF) is a protein that stimulates cell growth and differentiation by binding to its receptor, EGFR. Human EGF is 6-k Da and has 53 amino acid residues and three intramolecular disulfide bonds. EGF was originally descr ...

(EGF),

interferon-γ Interferon gamma (IFN-γ) is a dimerized soluble cytokine that is the only member of the type II class of interferons. The existence of this interferon, which early in its history was known as immune interferon, was described by E. F. Wheelock ...

and tumor necrosis factor (

TNF Tumor necrosis factor (TNF, cachexin, or cachectin; formerly known as tumor necrosis factor alpha or TNF-α) is an adipokine and a cytokine. TNF is a member of the TNF superfamily, which consists of various transmembrane proteins with a homolog ...

)-α. Therefore, it provides a cross-talk between TGF-β signaling and other cellular signaling pathways.

Role in cancer

A mutation located in SMAD7 gene is a cause of susceptibility to

colorectal cancer Colorectal cancer (CRC), also known as bowel cancer, colon cancer, or rectal cancer, is the development of cancer from the colon or rectum (parts of the large intestine). Signs and symptoms may include blood in the stool, a change in bowel m ...

(CRC) type 3. Perturbation of Smad7 and suppression of TGF-β signaling was found to be evolved in CRC. Case control studies and

meta-analysis A meta-analysis is a statistical analysis that combines the results of multiple scientific studies. Meta-analyses can be performed when there are multiple scientific studies addressing the same question, with each individual study reporting me ...

in Asian and European populations also provided evidence that this mutation is associated with colorectal cancer risk. TGF-β is one of the important growth factors in

pancreatic cancer Pancreatic cancer arises when cell (biology), cells in the pancreas, a glandular organ behind the stomach, begin to multiply out of control and form a Neoplasm, mass. These cancerous cells have the malignant, ability to invade other parts of t ...

. By controlling the TGF-β pathway, smad7 is believed to be related to this disease. Some previous study showed over-expression of Smad7 in pancreatic cells but there was a recent study showed a low Smad7 expression. The role of Smad7 in pancreatic cancer is still controversial. Over-expression or constitutive activation of

epidermal growth factor receptor The epidermal growth factor receptor (EGFR; ErbB-1; HER1 in humans) is a transmembrane protein that is a receptor for members of the epidermal growth factor family (EGF family) of extracellular protein ligands. The epidermal growth factor recept ...

(EGFR) can promote tumor processes. EGF-induced

MMP-9 Matrix metallopeptidase 9 (MMP-9), also known as 92 kDa type IV collagenase, 92 kDa gelatinase or gelatinase B (GELB), is a matrixin, a class of enzymes that belong to the zinc-metalloproteinases family involved in the degradation of the extracel ...

expression enhances tumor invasion and

metastasis Metastasis is a pathogenic agent's spread from an initial or primary site to a different or secondary site within the host's body; the term is typically used when referring to metastasis by a cancerous tumor. The newly pathological sites, then, ...

in some kinds of tumor cells such as

breast cancer Breast cancer is cancer that develops from breast tissue. Signs of breast cancer may include a lump in the breast, a change in breast shape, dimpling of the skin, milk rejection, fluid coming from the nipple, a newly inverted nipple, or a re ...

and

ovarian cancer Ovarian cancer is a cancerous tumor of an ovary. It may originate from the ovary itself or more commonly from communicating nearby structures such as fallopian tubes or the inner lining of the abdomen. The ovary is made up of three different c ...

. Smad7 exerts an inhibitory effect on the EGF signaling pathway. Therefore, it may play a role in prevention of cancer metastasis.

Use in Pharmacology

SMAD7 signaling has been studied in a recent Celgene Phase III trial, NCT ID number 94, which interacts with the SMAD7 pathway. This drug (Mongersen) was studied in patients with Crohn's disease.

Interactions

Mothers against decapentaplegic homolog 7 has been shown to

interact Advocates for Informed Choice, dba interACT or interACT Advocates for Intersex Youth, is a 501(c)(3) nonprofit organization using innovative strategies to advocate for the legal and human rights of children with intersex traits. The organizati ...

with: *

CTNNB1 Catenin beta-1, also known as beta-catenin (β-catenin), is a protein that in humans is encoded by the ''CTNNB1'' gene. Beta-catenin is a dual function protein, involved in regulation and coordination of cell–cell adhesion and gene transcripti ...

, *

EP300 Histone acetyltransferase p300 also known as p300 HAT or E1A-associated protein p300 (where E1A = adenovirus early region 1A) also known as EP300 or p300 is an enzyme that, in humans, is encoded by the ''EP300'' gene. It functions as histone ace ...

, *

TAB1 Mitogen-activated protein kinase kinase kinase 7-interacting protein 1 is an enzyme that in humans is encoded by the ''TAB1'' gene. Function The protein encoded by this gene was identified as a regulator of the MAP kinase kinase kinase MAP3K7/ ...

, *

PIAS4 E3 SUMO-protein ligase PIAS4 is one of several protein inhibitor of activated STAT (PIAS) proteins. It is also known as protein inhibitor of activated STAT protein gamma (PIASg or PIASy), and is an enzyme that in humans is encoded by the ''PIAS4' ...

, * RNF111, *

SMAD3 Mothers against decapentaplegic homolog 3 also known as SMAD family member 3 or SMAD3 is a protein that in humans is encoded by the SMAD3 gene. SMAD3 is a member of the SMAD family of proteins. It acts as a mediator of the signals initiated by t ...

. *

SMAD6 SMAD family member 6, also known as SMAD6, is a protein that in humans is encoded by the ''SMAD6'' gene. SMAD6 is a protein that, as its name describes, is a homolog of the Drosophila gene " mothers against decapentaplegic". It belongs to the SM ...

, *

STRAP A strap, sometimes also called strop, is an elongated wikt:flap, flap or ribbon, usually of leather or other flexible materials. Thin straps are used as part of clothing or baggage, or bedding such as a sleeping bag. See for example spaghetti s ...

, *

TGFBR1 Transforming growth factor beta receptor I (activin A receptor type II-like kinase, 53kDa) is a membrane-bound TGF beta receptor protein of the TGF-beta receptor family for the TGF beta superfamily of signaling ligands. ''TGFBR1'' is its human ...

, and *

YAP1 YAP1 (yes-associated protein 1), also known as YAP or YAP65, is a protein that acts as a transcription coregulator that promotes transcription of genes involved in cellular proliferation and suppressing apoptotic genes. YAP1 is a component in th ...

Structure

Function

Role in cancer

Use in Pharmacology

Interactions

References

Further reading