CAMSAP2 | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Aliases | CAMSAP2 , CAMSAP1L1, calmodulin regulated spectrin associated protein family member 2 | ||||||||||||||||||||||||||||||||||||||||||||||||||
External IDs | OMIM: 613775 MGI: 1922434 HomoloGene: 18927 GeneCards: CAMSAP2 | ||||||||||||||||||||||||||||||||||||||||||||||||||
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Calmodulin-regulated spectrin-associated protein family member 2 (CAMSAP2) is a protein that, in humans, is encoded by the CAMSAP2 gene. [5] CAMSAP2 possesses a microtubule-binding domain near the C-terminal region where said microtubule interactions occur. On these C-terminal regions, protein-protein interactions are accelerated by three coiled-coil domains, which function as molecular spacers. [6] CAMSAP2 acts as a microtubule minus-end anchor and binds microtubules through its CKK domain. CAMSAP2 is necessary for the proper organization and stabilization of interphase microtubules. The protein also plays a vital role in cell migration. [7] CAMSAP2 can stabilize and attach microtubule minus ends to the Golgi through the AKAP9 complex and myomegalin. CLASP1 proteins responsible for microtubule stability are not required for the Golgi tethering. When no centromeres are present, AKAP9 and CAMSAP-2 dependent pathways of these microtubule minus ends become a dominant force and must exist in order to observe the maintenance of microtubule density. [8]
Microtubules are cytoskeletal polymers with structurally and functionally different ends. There exists a plus-end and a minus-end on each microtubule. The CAMSAP family of proteins contributes to regulating the minus-ends of microtubules. [12] CAMSAP2 contains a CKK domain that binds to microtubules. This CKK domain is a defining factor of the CAMSAP protein family. It enables CAMSAP2 to recognize and bind to microtubule minus ends and allows CAMSAP2 to decorate and stabilize the microtubule lattice formed by minus-end polymerization. [13] In addition to a CKK domain, CAMSAP2 contains an N-terminal calponin homology domain involved with actin binding. [14]
CAMSAP2 proteins are observed to be primarily responsible for the maintenance of non-centrosomal microtubules. In epithelial cells, major microtubules are not anchored to the centrosome, which can be observed in other cell types. CAMSAP2 cooperates with calmodulin-regulated spectrin-associated protein 3 (CAMSAP3) to achieve the organization observed in these non-centrosomal microtubules. They possess the ability to suppress the organization of microtubules by the centrosome, and this family of proteins is important for the suitable arrangement of organelles in the cell body. These proteins gathered at the minus ends of these non-centrosomal microtubules can stabilize them. Without these proteins, the Golgi apparatus would exhibit irregular distributions of the microtubules. [15]
In pancreatic β-cells, glucose stimulation leads to the remodeling of microtubules responsible for insulin secretion. CAMSAP2 binds to the minus ends of microtubules in normal clonal cells. The knockdown of CAMSAP2 in these β-cells reduces the total insulin content secreted through glucose-stimulated insulin secretion. However, CAMSAP2 localizes to the Golgi apparatus instead of the microtubule minus ends. This oddity is observed only in β-cells as opposed to α-cells. With this collection at the Golgi apparatus, CAMSAP2 promotes the protein trafficking of the Golgi, efficiently facilitating the process. Without CAMSAP2, there would not be adequate insulin production for secretion from these β-cells. [16]
CAMSAP2-dependent microtubule organization promotes directional cell migration. CAMSAP2 is required for the proper organization of non-centrosomal interphase molecules. Depletion of CAMSAP2 leads to a mostly centrosome-anchored, radial microtubule array. CAMSAP2. CAMSAP2 is responsible for cell polarization because the stretches of CAMSAP2-decorated microtubules enable proper microtubule organization to achieve spatial redistribution and functional specialization of components in the cell. In wound healing assays, CAMSAP2 depletion reduced the ability of cells to close a wound, indicating impaired directional migration. [17] CAMSAP2 populates the cytoplasm with microtubules, allowing the cell to regenerate its cytoskeleton and facilitate effective cell migration.
The initial polymerization of microtubules can be called microtubule nucleation. This process occurs spontaneously via soluble αβ-tubulin dimers. Microtubule nucleation normally requires overcoming a large energy barrier inside of cells. Typically, a γ-tubulin ring complex is recruited to facilitate the nucleation process; however, CAMSAP2 can act as a strong nucleating agent for microtubule formation independent of this γ-tubulin. CAMSAP2 significantly reduces the nucleation energy barrier by stabilizing longitudinal interactions between the αβ-tubulin dimers, thereby increasing the critical concentration for nucleation. CAMSAP2 achieves this increase by clustering with the αβ-tubulin dimers to generate intermediates from which multiple microtubules can originate, promoting new astral microtubule growth. [19]
CAMSAP2 is responsible for controlling axon specification and dendrite development. In the brain, neurons normally are not associated with any central microtubule-organizing centers (MTOC). This phenomenon sees the existence of free minus and plus-ends throughout the cell. As stated previously, CAMSAP2 has an affinity for binding to free microtubule minus ends in the cell. The stabilization CAMSAP2 can achieve by binding to the free ends of these microtubules is quite important in regulating neuronal polarity. These highly polarized neurons are formed in the developing neocortex, and the centrosome loses its function as an MTOC. CAMSAP2 structures' stability-providing qualities ensure the fate of the axon and the development of neuronal polarity needed for neocortex development. Neurons lacking CAMSAP2 fail to begin axon formation and lack neuronal polarization. [20]
CAMSAP2 is involved in targeting microtubule minus-ends in Sertoli cell function. Sertoli cells are intrinsically polarized, with minus ends pointing toward the tubule lumen and plus ends toward the basement membrane of the seminiferous epithelium. [21] The protein was found throughout the Sertoli cell cytosol colocalized with microtubules. These Sertoli cells are responsible for regulating the blood-testis barrier. CAMSAP2 appears along the seminiferous epithelium close to the basement membrane. It increases the function of the Sertoli cell tight junction. All of the microtubule-based tracks in Sertoli cells are crucial for the intracellular transport of organelles. CAMPSAP2 is bound to the minus-ends of microtubules, slowing down the polymerization of free tubulins and effectively regulating their growth. By knocking down CAMSAP2 proteins in these regions, the growth of these tracks could support spermatogenesis and BTB dynamics. In a model of Sertoli cell injury, this knockdown of the CAMSAP2 promoted Sertoli cell tight junction barrier function, which suggests its role in tight junction remodeling. CAMSAP2 knockdown blocked the disruptive organization of microtubules and actin filaments caused by the injury, enabling proper distribution of BTB-associated proteins at the cell junctions. [21]
CAMSAP2 plays a significant role in the migration of cancer cells. It has been observed that CAMSAP2 is severely upregulated in cancers such as hepatocellular carcinoma (HCC). When placed in an assay of liver samples, an outgrowth of HCC cells was observed. Upon the depletion of CAMSAP2 from these samples, a drop in the prevalence of acetylated microtubules occurred. CAMSAP2 exhibited tumor-suppressing qualities by downregulating the histone deacetylase 6 (HDAC6) promoter region. CAMSAP2 activates a c-Jun transrepression of HDAC6 along the Trio-dependent Rac1/JNK pathway, inhibiting CAMSAP2-mediated HCC metastasis. [22]
CAMPSAP promotes the migration of colorectal cancer cells by activating the JNK/c-Jun/MMP-1 signaling pathway. Acting as an oncogene, CAMSAP2 promotes the capabilities of migration in colorectal cells. Through the silencing of this gene, the substantial downstream target, MMP-1, regulated the invasion of these cells and slowed down disease progress. Metastasis of this cancer permeates through the activation of this signaling pathway and indicates CAMSAP2 as a promising target for treating metastatic colorectal cancer patients. [23]
An association between CAMSAP2 expression levels and the progression and prognosis of gastric cancer was investigated in 2023. [24] This investigation into the expression of the CAMSAP2 protein in gastric cancer aimed to understand its effects on cell invasion and metastasis. [25] One hundred six cancer patients underwent a radical gastrectomy, and they analyzed the expression levels of CAMSAP2 proteins. Gastric cancer MGC803 cells with CAMSAP2 overexpression and knockdown were studied for epithelial-mesenchymal transition, where epithelial cells acquire the invasive characteristics of mesenchymal cells. Researchers utilized a nude mouse model with orthotopic gastric cancer cell xenografts to verify the in vitro results. The scientists discovered that gastric cancer tissues demonstrated high levels of CAMSAP2. These results positively correlated with tumor markers carcinoembryonic antigen and CA19-9. Bioinformatics analysis suggested CAMSAP2 is involved in epithelial-mesenchymal transition and the upregulation of TGF-β signaling. In the mouse model, CAMSAP2 overexpressing xenografts illustrated enhanced metastasis, increased vimentin and N-cadherin, and decreased E-cadherin. The high expression of CAMSAP2 contributes to gastric cancer progression and poor prognosis by the upregulation of TGF-β signaling. [24]
Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nm and have an inner diameter between 11 and 15 nm. They are formed by the polymerization of a dimer of two globular proteins, alpha and beta tubulin into protofilaments that can then associate laterally to form a hollow tube, the microtubule. The most common form of a microtubule consists of 13 protofilaments in the tubular arrangement.
In cell biology, the spindle apparatus is the cytoskeletal structure of eukaryotic cells that forms during cell division to separate sister chromatids between daughter cells. It is referred to as the mitotic spindle during mitosis, a process that produces genetically identical daughter cells, or the meiotic spindle during meiosis, a process that produces gametes with half the number of chromosomes of the parent cell.
The microtubule-organizing center (MTOC) is a structure found in eukaryotic cells from which microtubules emerge. MTOCs have two main functions: the organization of eukaryotic flagella and cilia and the organization of the mitotic and meiotic spindle apparatus, which separate the chromosomes during cell division. The MTOC is a major site of microtubule nucleation and can be visualized in cells by immunohistochemical detection of γ-tubulin. The morphological characteristics of MTOCs vary between the different phyla and kingdoms. In animals, the two most important types of MTOCs are 1) the basal bodies associated with cilia and flagella and 2) the centrosome associated with spindle formation.
Tubulin in molecular biology can refer either to the tubulin protein superfamily of globular proteins, or one of the member proteins of that superfamily. α- and β-tubulins polymerize into microtubules, a major component of the eukaryotic cytoskeleton. Microtubules function in many essential cellular processes, including mitosis. Tubulin-binding drugs kill cancerous cells by inhibiting microtubule dynamics, which are required for DNA segregation and therefore cell division.
In molecular biology, treadmilling is a phenomenon observed within protein filaments of the cytoskeletons of many cells, especially in actin filaments and microtubules. It occurs when one end of a filament grows in length while the other end shrinks, resulting in a section of filament seemingly "moving" across a stratum or the cytosol. This is due to the constant removal of the protein subunits from these filaments at one end of the filament, while protein subunits are constantly added at the other end. Treadmilling was discovered by Wegner, who defined the thermodynamic and kinetic constraints. Wegner recognized that: “The equilibrium constant (K) for association of a monomer with a polymer is the same at both ends, since the addition of a monomer to each end leads to the same polymer.”; a simple reversible polymer can’t treadmill; ATP hydrolysis is required. GTP is hydrolyzed for microtubule treadmilling.
In biology, a protein filament is a long chain of protein monomers, such as those found in hair, muscle, or in flagella. Protein filaments form together to make the cytoskeleton of the cell. They are often bundled together to provide support, strength, and rigidity to the cell. When the filaments are packed up together, they are able to form three different cellular parts. The three major classes of protein filaments that make up the cytoskeleton include: actin filaments, microtubules and intermediate filaments.
In cell biology, microtubule nucleation is the event that initiates de novo formation of microtubules (MTs). These filaments of the cytoskeleton typically form through polymerization of α- and β-tubulin dimers, the basic building blocks of the microtubule, which initially interact to nucleate a seed from which the filament elongates.
Class III β-tubulin, otherwise known as βIII-tubulin (β3-tubulin) or β-tubulin III, is a microtubule element of the tubulin family found almost exclusively in neurons, and in testis cells. In humans, it is encoded by the TUBB3 gene.
Targeting protein for Xklp2 is a protein that in humans is encoded by the TPX2 gene. It is one of the many spindle assembly factors that play a key role in inducing microtubule assembly and growth during M phase.
Ninein is a protein that in humans is encoded by the NIN gene.
Gamma-tubulin complex component 2 is a protein that in humans is encoded by the TUBGCP2 gene. It is part of the gamma-tubulin complex, which is required for microtubule nucleation at the centrosome.
Neural precursor cell expressed, developmentally down-regulated 1, also known as Nedd1, is a human gene and encodes the protein NEDD1.
Centrosomal protein of 164 kDa, also known as CEP164, is a protein that in humans is encoded by the CEP164 gene. Its function appears two be twofold: CEP164 is required for primary cilium formation. Furthermore, it is an important component in the response to DNA damage by UV light.
Centrosomal protein of 152 kDa, also known as Cep152, is a protein that in humans is encoded by the CEP152 gene. It is the ortholog of the Drosophila melanogaster gene asterless (asl) and both are required for centriole duplication.
Protein Hook homolog 2 (HK2) is a protein that in humans is encoded by the HOOK2 gene.
AKNA is a protein that in humans is encoded by the AKNA gene. The protein is an AT-hook transcription factor which contains an AT-hook binding motif. The protein is expressed as different isoforms. AKNA is known to upregulate expression of the receptor CD40 and its ligand CD40L/CD154.
Tubulin, gamma 1 is a protein in humans that is encoded by the TUBG1 gene. This gene encodes a member of the tubulin superfamily. The encoded protein localizes to the centrosome where it binds to microtubules as part of a complex referred to as the gamma-tubulin ring complex. The protein mediates microtubule nucleation and is required for microtubule formation and progression of the cell cycle.
Tubulin, gamma complex associated protein 4 is a protein in humans that is encoded by the TUBGCP4 gene. It is part of the gamma tubulin complex, which required for microtubule nucleation at the centrosome.
Neurotubules are microtubules found in neurons in nervous tissues. Along with neurofilaments and microfilaments, they form the cytoskeleton of neurons. Neurotubules are undivided hollow cylinders that are made up of tubulin protein polymers and arrays parallel to the plasma membrane in neurons. Neurotubules have an outer diameter of about 23 nm and an inner diameter, also known as the central core, of about 12 nm. The wall of the neurotubules is about 5 nm in width. There is a non-opaque clear zone surrounding the neurotubule and it is about 40 nm in diameter. Like microtubules, neurotubules are greatly dynamic and the length of them can be adjusted by polymerization and depolymerization of tubulin.
Calmodulin-regulated spectrin-associated protein family member 3 (CAMSAP3) is a human protein encoded by the gene CAMSAP3. The protein is commonly referred to as Nezha.