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APC
APC regulator of Wnt signaling pathway
The APC gene, or APC regulator of Wnt signalling pathway, is crucial for regulating cell growth and division, acting as a tumour suppressor primarily associated with familial adenomatous polyposis (FAP). The APC gene provides instructions for the APC protein, which is vital in controlling cell proliferation and differentiation by regulating the Wnt signalling pathway.
APC is located on the long (q) arm of chromosome 5, at band 5q22.2. Arm ratio per GRCh38 - banding schematic.
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Overview
The APC gene, formally known as the APC regulator of Wnt signalling pathway, plays a fundamental role in maintaining cellular homeostasis by regulating critical processes such as cell growth, division, and differentiation [PMID:20301390]. It functions as a tumour suppressor, meaning it helps prevent uncontrolled cell proliferation, which is a hallmark of cancer development. The protein encoded by the APC gene is a key component in controlling the Wnt signalling pathway, a complex network that governs various cellular activities [PMID:10072352].
Dysregulation of the APC gene's function, often through inherited pathogenic variants, is primarily associated with familial adenomatous polyposis (FAP), a hereditary condition predisposing individuals to developing hundreds to thousands of precancerous growths, known as polyps, in the colon and rectum [PMID:20301390]. Without appropriate management, these polyps commonly progress to colorectal cancer. Understanding the APC gene's normal function and the implications of its variants is therefore crucial for early detection, diagnosis, and management of associated conditions.
What the gene does
The APC protein is a critical component of several fundamental cellular processes, acting primarily as a tumour suppressor to prevent uncontrolled cell growth and division. Its main mechanism of action involves regulating the Wnt signalling pathway, which is instrumental in promoting cell proliferation and influencing the expression of specific genes. The APC protein achieves this by interacting with various other proteins to form a complex responsible for controlling the levels of beta-catenin, a key protein within the Wnt pathway.
Beta-catenin is central to numerous cell functions, including proliferation, gene expression, and cellular differentiation. When the APC protein complex binds beta-catenin, it promotes its degradation once the protein has fulfilled its signalling role, thereby downregulating Wnt signalling [PMID:10072352]. This regulatory action ensures that cell growth and division remain tightly controlled. A specific region spanning amino acids 960-1337 is responsible for this down-regulation through a process mediated by direct ubiquitination, while the interaction with catenins occurs within the region of amino acids 1020-1169.
Beyond its role in Wnt signalling, the APC protein also contributes to the precise regulation of cell division. It interacts with components of the cell's cytoskeleton, the internal scaffolding that provides structural support and helps organise the cell. This interaction is essential for proper cell organisation during the division process, helping to ensure that daughter cells receive the correct number of chromosomes following cell division [PMID:10072352]. By ensuring proper chromosome distribution, APC helps cells preserve their normal chromosome count and reduces cancer-associated chromosomal abnormalities.
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Chromosome location
The APC gene is located on the long (q) arm of chromosome 5, specifically at position 5q22.2. This genomic location indicates its precise address within the human genome. The gene spans a significant length of DNA, encoding a protein comprising 2843 amino acids.
Protein structure
The APC protein, with a length of 2843 amino acids, exhibits a complex domain architecture crucial for its diverse functions. It features several coiled-coil domains, including one from amino acids 2-61 and another from amino acids 127-248. Disordered regions are present at amino acids 239-305, 828-878, 923-943, and 958-987, which often facilitate protein-protein interactions. The protein also contains multiple Armadillo (ARM) repeats, including ARM 1 (453-495) through ARM 7 (726-767).
A significant region from amino acids 960-1337 is responsible for the down-regulation of Wnt signalling through a process mediated by direct ubiquitination. Furthermore, an interaction with catenins, critical for Wnt pathway regulation, occurs within the region spanning amino acids 1020-1169. Additional disordered regions are found at 1099-1169, 1190-1244, 1311-1376, 1403-1475, and 1526-1569.
Key variants
Variants within the APC gene can significantly impact its tumour suppressor function, leading to a range of clinical presentations. These genetic changes can include various types, such as point mutations, small insertions or deletions, and larger structural alterations. The nature and location of an APC gene variant can influence the severity and specific manifestations of associated conditions. Pathogenic variants often result in a truncated or non-functional APC protein, impairing its ability to regulate the Wnt signalling pathway and control cell proliferation. Given its role as an ACMG SF v3.2 - Secondary Finding gene, detection of pathogenic APC variants may have significant health implications, even when not specifically sought. The inheritance pattern for conditions linked to APC is typically autosomal dominant.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.1311_1312+1del | - | Pathogenic | ★★★☆ | Familial adenomatous polyposis 1 |
c.1312+3A>G | - | Pathogenic | ★★★☆ | not provided |
c.1333C>T | p.Gln445Ter | Pathogenic | ★★★☆ | not provided |
c.1900dup | p.Ser634fs | Pathogenic | ★★★☆ | Familial adenomatous polyposis 1 |
c.203del | p.Leu68fs | Pathogenic | ★★★☆ | Hereditary cancer-predisposing syndrome |
c.220+1G>A | - | Pathogenic | ★★★☆ | Familial adenomatous polyposis 1 |
c.220+2T>A | - | Pathogenic | ★★★☆ | Hereditary cancer-predisposing syndrome |
c.2240C>G | p.Ser747Ter | Pathogenic | ★★★☆ | Hereditary cancer-predisposing syndrome |
c.2546_2552del | p.Asp849fs | Pathogenic | ★★★☆ | Familial adenomatous polyposis 1 |
c.3927_3931del | p.Glu1309fs | Pathogenic | ★★★☆ | Gardner syndrome |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Pathogenic variants in the APC gene are primarily associated with several inherited conditions, most notably familial adenomatous polyposis (FAP). FAP is characterised by the development of hundreds to thousands of precancerous polyps in the colon and rectum, which carry a very high risk of progressing to colorectal cancer if not managed. Other conditions linked to APC variants include desmoid tumours, which are aggressive but non-cancerous growths arising from connective tissue, and gastric adenocarcinoma and proximal polyposis of the stomach (GAPPS), characterised by numerous polyps in the stomach and an increased risk of gastric cancer. There is also an association with primary macronodular adrenal hyperplasia.
Inheritance pattern
Conditions caused by pathogenic APC variants typically follow autosomal dominant inheritance.
Each child has a 50% chance of inheriting the pathogenic variant, regardless of sex.
UK clinical status
In the UK, the APC gene is recognised for its clinical significance and is included in several NHS England Genomic Medicine Service (GMS) national genomic testing panels, as detailed in PanelApp. It is listed on panels such as 'Additional findings health related', 'Adult solid tumours cancer susceptibility', and 'Colorectal cancer pertinent cancer susceptibility'. These inclusions highlight its importance in identifying individuals at risk for various cancers and other related conditions, ensuring appropriate surveillance and management pathways are offered.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Diet & lifestyle considerations
Research in the general population has observed associations between certain lifestyle factors and overall health outcomes. For instance, a balanced diet that includes plenty of fruits, vegetables, and whole grains is often linked to better digestive health. Some studies suggest a correlation between limiting red and processed meats and a reduced risk of colorectal cancer. Similarly, regular physical activity and maintaining a healthy body weight are broadly recognised for their positive influence on general well-being and may play a role in reducing cancer risk in the wider population. Avoiding smoking and excessive alcohol consumption are also considered important for overall health. These are general observations and not specific recommendations for individuals with APC variants; any lifestyle changes should be discussed with a healthcare provider in the context of individual circumstances.
Supplement considerations
Currently, there is no conclusive scientific evidence to suggest that specific dietary supplements can prevent the development or progression of conditions associated with APC gene variants, such as familial adenomatous polyposis (FAP). While some research explores the potential roles of various micronutrients and natural compounds in cancer prevention, these findings are often preliminary and not specific to individuals with APC-related conditions.
For instance, some studies have investigated the role of calcium and vitamin D in colorectal cancer prevention, but these are general observations in the broader population and not tailored advice for those with pathogenic APC variants. Individuals considering any supplements should discuss this with a healthcare professional to ensure they are safe and appropriate, as supplements can interact with medications or have unintended effects. A balanced diet generally provides sufficient nutrients for most people.
Frequently asked questions
What does the APC gene do?
The APC gene provides instructions for making the APC protein, which acts as a tumour suppressor. It helps regulate cell growth, division, and differentiation by controlling the Wnt signalling pathway, ensuring cells do not grow too quickly or uncontrollably.
What conditions are associated with pathogenic APC variants?
Pathogenic variants in the APC gene are primarily associated with familial adenomatous polyposis (FAP), desmoid tumours, and gastric adenocarcinoma and proximal polyposis of the stomach (GAPPS). There is also an association with primary macronodular adrenal hyperplasia.
How are conditions related to APC variants inherited?
Conditions linked to pathogenic APC variants, such as familial adenomatous polyposis (FAP), are typically inherited in an autosomal dominant pattern. This means that a person only needs to inherit one copy of the altered gene from a parent to be affected.
What is familial adenomatous polyposis (FAP)?
Familial adenomatous polyposis (FAP) is a hereditary condition characterised by the development of hundreds to thousands of precancerous polyps in the colon and rectum. These polyps have a very high risk of becoming cancerous if not detected and managed appropriately.
Is the APC gene considered an actionable gene in the UK?
Yes, the APC gene is recognised as clinically significant in the UK and is included in several NHS England Genomic Medicine Service national genomic testing panels, such as 'Adult solid tumours cancer susceptibility' and 'Colorectal cancer pertinent cancer susceptibility'.
Can lifestyle changes prevent APC-related conditions?
While no lifestyle changes can prevent inherited APC-related conditions, adopting a healthy lifestyle with a balanced diet, regular exercise, maintaining a healthy weight, and avoiding smoking and excessive alcohol can contribute to overall health and may reduce general cancer risk.
References
- Lips DJ, Barker N, Clevers H. The role of APC and beta-catenin in the aetiology of aggressive fibromatosis (desmoid tumors). European journal of surgical oncology : the journal of the European Society of Surgical Oncology and the British Association of Surgical Oncology. 2009. PMID: 18722078
- Sena P, Saviano M, Monni S. Subcellular localization of beta-catenin and APC proteins in colorectal preneoplastic and neoplastic lesions. Cancer letters. 2006. PMID: 16298038
- Jaiswal AS, Balusu R, Narayan S. Involvement of adenomatous polyposis coli in colorectal tumorigenesis. Frontiers in bioscience : a journal and virtual library. 2005. PMID: 15769611
- Tejpar S, Michils G, Denys H. Analysis of Wnt/Beta catenin signalling in desmoid tumors. Acta gastro-enterologica Belgica. 2005. PMID: 15832580
- Senda T, Shimomura A, Iizuka-Kogo A. Adenomatous polyposis coli (Apc) tumor suppressor gene as a multifunctional gene. Anatomical science international. 2005. PMID: 16158975