Lymphotoxin alpha
Ensembl |
| ||||||||
---|---|---|---|---|---|---|---|---|---|
UniProt | |||||||||
RefSeq (mRNA) | |||||||||
RefSeq (protein) | |||||||||
Location (UCSC) | Chr 6: 31.57 – 31.57 Mb | Chr 17: 35.42 – 35.42 Mb | |||||||
PubMed search | [3] | [4] |
View/Edit Human | View/Edit Mouse |
Lymphotoxin-alpha (LT-α) formerly known as tumor necrosis factor-beta (TNF-β)
LT-α has a significant impact on the maintenance of the immune system including the development of
As a signaling molecule, LT-α is involved in the regulation of cell survival, proliferation, differentiation, and apoptosis.[13] LT-α plays an important role in innate immune regulation and its presence has been shown to prevent tumor growth and destroy cancerous cell lines.[14] In contrast, unregulated expression of LT-α can result in a constantly active signaling pathway, thus leading to uncontrolled cellular growth and creation of tumors.[13] Hence depending on the context, LT-α may function to prevent growth of cancer cells or facilitate the development of tumors. Furthermore, LT-α effects depend on the type of organ it acts upon, type of cancer cells, cellular environment, gender, and time of effect during an immune response.[15][14]
Gene
The human gene encoding for LT-α was cloned in 1985.
Structure
LT-α is translated as a 25 kDa glycosylated polypeptide with 171 amino acid residues.[8] Furthermore, human LT-α is 72% identical to mouse LT-α at the protein's primary sequence.[18]
LTα expression is highly inducible and when secreted, forms a soluble homotrimeric molecule. LT-α can also form heterotrimers with lymphotoxin-beta, which anchors lymphotoxin-alpha to the cell surface. The interaction between LT-α and LT-β results in the formation of a membrane bound complex (LT-α1-β2).[11]
Function
Lymphotoxin alpha, a member of the tumor necrosis factor superfamily, is a cytokine produced by lymphocytes. LT-α1-β2 can interact with receptors such as LT-β receptors.[13] Absence of LT-β on cell surfaces will diminish the ability of LT-α to form LT-α1-β2, thus decreasing its effective ability as a cytokine.[10][11] LT-α mediates a large variety of inflammatory, immunostimulatory, and antiviral responses. LT-α is also involved in the formation of secondary lymphoid organs during development and plays a role in apoptosis.[19]
In LT-α knockout mice, Peyer's patches and lymph nodes will fail to develop, thus illustrating the cytokine's essential role in immunological development.[20]
As a cytotoxic protein, LT-α causes the destruction of cancerous cell lines, activates signaling pathways, and effectively kills transformed tumor cells.[10][13] However, mice with overexpression of LT-α or LT-β showed increased tumor growth and metastasis in several models of cancer. In other studies, mice with gene knockout of LT-α showed enhanced tumor growth, implicating possible protective role of LT-α in cancer. However, these studies utilized mice with complete LT-α deficiency that did not allow to distinguish effects of soluble versus membrane-associated LT.[21]
LT-α mediated signaling pathway
As a member of the
Anti-carcinogenic properties
Activation of LT-β receptors is capable of inducing cell death of cancerous cells and suppressing tumor growth.[24][25] The process of cell death is mediated by the presence of IFN-γ and can involve apoptotic or necrotic pathways.[24] It is seen that LT-β receptors facilitate the upregulation of adhesion molecules and recruit lymphocytes to tumor cells to combat tumor growth.[7][13] In other words, LT-α interactions with LT-β receptors can increase anti-tumor effects through direct destruction of tumor cells.
Pro-carcinogenic properties
However, recent studies have shown the contribution of LT-α mediated signaling to the development of cancer.[10][13][14][15] As mentioned previously, LT-α signaling can promote inflammatory responses, but prolonged inflammation can cause serious cellular damage and increase the risk of certain diseases including cancer.[14] Thus, mutations in regulatory factors in LT-α signaling pathways can promote cell signaling disruptions and encourage the creation of cancerous cell lines. One of these mutations includes constant binding of LT-α1-β2 complex to LT-β receptors, which results in the constant activation of the NF-κB alternative pathway.[13][14] Presence of a constitutively active NF-κB pathway manifests in multiple myeloma and other cancer-related diseases.[13] Removal of LT-β receptors has shown to inhibit tumor growth and decrease angiogenesis.[14] Thus, lymphotoxin and its downstream signaling via the NF-κB pathway illustrate the cytokine's influence on tumor development and metastasis.
A fully humanized anti-LT-α antibody (Pateclizumab or MLTA3698A) has been shown to react with both LT-α and LT-β.[10] Clinical trials involving this antibody have yet to be employed, but the creation of this antibody offers alternative inhibitory methods for the NF-κB pathway.
Effects on gastrointestinal system
During embryonic development, LT-α signaling plays an active part in the formation of the gastrointestinal immune system.[12] In particular, LT-α mediated signaling is responsible for the development of intestinal lymphoid structures such as Peyer’s patches.[26][27] This intestinal lymphoid follicle plays an important role in the immune system of the digestive tract.
Peyer’s patches are highly specialized lymphoid nodules located in the intestine. They are surrounded by follicle-associated epithelium and are able to interact with other immune cells through the transcytosis of foreign antigens.[28] In addition to this function, Peyer’s patches facilitate the production Ig-A producing immunocytes, thus increasing the efficacy of the adaptive immune system.[29]
The development of Peyer’s patches requires the binding and activation of LT-β receptor with LT-α1-β2 complex. Experiments involving transgenic mice have shown that the absence of LT-α resulted in the lack of Peyer’s patches and other lymph nodes.[12] The lack of Peyer’s patches and other lymph nodes have also been shown to reduce levels of Ig-A.[12] Being the most produced immunoglobulin, Ig-A protects against mucosal pathogens by regulating bacterial growth and inhibiting antigen adhesion to the intestine under normal conditions.[30] Reduced levels of Ig-A greatly diminishes gut immune regulation and deregulate protection against microbes, thereby emphasizing the importance of LT-mediated response for the expression of Ig-A.
Nomenclature
Discovered by Granger and his research group in 1968, LT-alpha was known as lymphotoxin.[31] As years progressed, its name was changed to tumor necrosis factor-beta (TNF-β).[32] Later discovery of LT-β and LT-α1-β2 complex prompted the disposal of TNF-β and the subdivision of LT into two classes: LT-α and LT-β.[33][34]
Interactions
Lymphotoxin alpha has been shown to
See also
References
- ^ a b c ENSG00000223919, ENSG00000173503, ENSG00000226275, ENSG00000230279, ENSG00000238130, ENSG00000226979 GRCh38: Ensembl release 89: ENSG00000231408, ENSG00000223919, ENSG00000173503, ENSG00000226275, ENSG00000230279, ENSG00000238130, ENSG00000226979 – Ensembl, May 2017
- ^ a b c GRCm38: Ensembl release 89: ENSMUSG00000024402 – Ensembl, May 2017
- ^ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
- ^ "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
- ^ "Lymphotoxin Alpha - an overview | ScienceDirect Topics".
- ^ Calmon-Hamaty F, Combe B, Hahne M, Morel J. Lymphotoxin α revisited: general features and implications in rheumatoid arthritis. Arthritis Res Ther. 2011 Jul 26;13(4):232. doi: 10.1186/ar3376. PMID 21861866; PMCID: PMC3239340.
- ^ PMID 2995927.
- ^ S2CID 4341571.
- PMID 21861866.
- ^ PMID 24636534.
- ^ PMID 9892622.
- ^ S2CID 15764230.
- ^ S2CID 13165828.
- ^ PMID 26923876.
- ^ S2CID 42014048.
- PMID 7846035.
- PMID 3490653.
- S2CID 4245957.
- ^ "Entrez Gene: LTA lymphotoxin alpha (TNF superfamily, member 1)".
- ISBN 978-0-7817-6519-0.
- PMID 26854213.
- ^ PMID 12556537.
- PMID 12505990.
- ^ PMID 8642291.
- PMID 17018619.
- PMID 10358764.
- PMID 18370924.
- PMID 18668776.
- PMID 4934147.
- S2CID 2586305.
- S2CID 4171855.
- S2CID 22218299.
- S2CID 28961163.
- PMID 9133428.
- PMID 9235946.
- S2CID 25608697.
- S2CID 22313274.
Further reading
- Körner H, Sedgwick JD (October 1996). "Tumour necrosis factor and lymphotoxin: molecular aspects and role in tissue-specific autoimmunity". Immunology and Cell Biology. 74 (5): 465–72. S2CID 22305752.
- Wang Q (May 2005). "Molecular genetics of coronary artery disease". Current Opinion in Cardiology. 20 (3): 182–8. PMID 15861005.
- Copeland KF (December 2005). "Modulation of HIV-1 transcription by cytokines and chemokines". Mini Reviews in Medicinal Chemistry. 5 (12): 1093–101. PMID 16375755.
- Elewaut D, Ware CF (April 2007). "The unconventional role of LT alpha beta in T cell differentiation". Trends in Immunology. 28 (4): 169–75. PMID 17336158.