Calmodulin-regulated spectrin-associated protein family member 2 (CAMSAP2) is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

in humans that is encoded by the CAMSAP2

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

. CAMSAP2 possesses a microtubule-binding domain near the C-terminal region where "microtubule interactions" occur. On the C-terminal regions, protein to protein interactions are accelerated by three

coiled-coil A coiled coil is a structural motif in proteins in which two to seven alpha-helices are coiled together like the strands of a rope. ( Dimers and trimers are the most common types.) They have been found in roughly 5-10% of proteins and have a v ...

domains, which function as molecular spacers. 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 role in cell migration. CAMSAP2 stabilizes and attaches microtubule minus ends to the Golgi through the

AKAP9 A-kinase anchor protein 9 is a protein that in humans is encoded by the ''AKAP9'' gene. AKAP9 is also known as Centrosome- and Golgi-localized protein kinase N-associated protein (CG-NAP) or AKAP350 or AKAP450 Function The A-kinase anchor pro ...

complex and

myomegalin Myomegalin, also known as phosphodiesterase 4D-interacting protein or cardiomyopathy-associated protein 2, is a protein that in humans is encoded by the ''PDE4DIP'' gene. It has roles in the Microtubule nucleation, formation of microtubules from ...

CLASP1 Cytoplasmic linker associated protein 1, also known as CLASP1, is a protein which in humans is encoded by the ''CLASP1'' gene. Function CLASP1 belongs to a family of microtubule-associated proteins involved in attachment of microtubules to th ...

proteins are responsible for microtubule stability which are not required for the Golgi tethering. When no centromeres are present, AKAP9 and CAMSAP-2 dependent pathways of the microtubule minus ends become a dominant force and must exist in order to observe the maintenance of microtubule density.

Structure

Microtubules 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 an ...

are cytoskeletal

polymers A polymer () is a substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeating subunits derived from one or more species of monomers. Due to their broad spectrum of properties, b ...

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. CAMSAP2 contains a CKK domain that binds to microtubules. The specific 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 In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...

. In addition to a CKK domain, CAMSAP2 contains an N-terminal

calponin homology domain Calponin homology domain (or CH domain) is a family of actin binding domains found in both cytoskeletal proteins and signal transduction proteins. The domain is about 100 amino acids in length and is composed of four alpha helices. It comprise ...

involved with actin binding.

Function

Non-centrosomal microtubule maintenance

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

CAMSAP3 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. Function CAMSAP3 acts as a minus-end anchor of microtubules, and binds to th ...

to achieve the organization observed in the non-centrosomal microtubules. They possess the ability to suppress the organization of microtubules by the centrosome, and the specific family of proteins is important for the suitable arrangement of organelles in the cell body. The proteins gathered at the minus ends of the non-centrosomal microtubules can stabilize them. Without these proteins, the Golgi apparatus would exhibit irregular distributions of the microtubules.

Pancreatic islet cells

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 the β-cells reduces the total insulin content secreted through glucose-stimulated insulin secretion. CAMSAP2 localizes to the Golgi apparatus instead of the microtubule minus ends. The oddity is observed only in β-cells as opposed to α-cells. With the specific 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 the β-cells.

Migration

CAMSAP2-dependent microtubule organization promotes directional

cell migration Cell migration is a central process in the development and maintenance of multicellular organisms. Tissue formation during embryogenesis, embryonic development, wound healing and immune system, immune responses all require the orchestrated movemen ...

. 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 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. CAMSAP2 populates the cytoplasm with microtubules, allowing the cell to regenerate its

cytoskeleton The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is compos ...

and facilitate effective cell migration.

Microtubule nucleation

The initial polymerization of microtubules can be called "

microtubule nucleation 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 process occurs spontaneously via soluble αβ-tubulin dimers. Microtubule nucleation normally requires overcoming a large energy barrier inside of cells. Typically, a

γ-tubulin 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 cytos ...

ring complex is recruited to facilitate the

nucleation In thermodynamics, nucleation is the first step in the formation of either a new Phase (matter), thermodynamic phase or Crystal structure, structure via self-assembly or self-organization within a substance or mixture. Nucleation is typically def ...

process; however, CAMSAP2 can act as a strong nucleating agent for microtubule formation independent of the 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 the increase by clustering with the αβ-tubulin dimers to generate intermediates from which multiple microtubules can originate, promoting new astral microtubule growth.

Regulation

Regulator of neuronal polarity and development

CAMSAP2 is responsible for controlling

axon An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences) is a long, slender cellular extensions, projection of a nerve cell, or neuron, ...

specification and

dendrite A dendrite (from Ancient Greek language, Greek δένδρον ''déndron'', "tree") or dendron is a branched cytoplasmic process that extends from a nerve cell that propagates the neurotransmission, electrochemical stimulation received from oth ...

development. In the brain,

neurons A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

normally are not associated with any central microtubule-organizing centers ( MTOC). The phenomenon sees the existence of free minus and plus-ends throughout the cell. 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 the microtubules is important in regulating neuronal polarity. The highly polarized neurons are formed in the developing neocortex, and the

centrosome In cell biology, the centrosome (Latin centrum 'center' + Greek sōma 'body') (archaically cytocentre) is an organelle that serves as the main microtubule organizing center (MTOC) of the animal cell, as well as a regulator of cell-cycle progre ...

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.

Regulator of blood–testis barrier (BTB)

CAMSAP2 is involved in targeting microtubule minus-ends in

Sertoli cell Sertoli cells are a type of sustentacular "nurse" cell found in human testes which contribute to the process of spermatogenesis (the production of sperm) as a structural component of the seminiferous tubules. They are activated by follicle-sti ...

function. Sertoli cells are intrinsically polarized, with minus ends pointing toward the tubule lumen and plus ends toward the

basement membrane The basement membrane, also known as base membrane, is a thin, pliable sheet-like type of extracellular matrix that provides cell and tissue support and acts as a platform for complex signalling. The basement membrane sits between epithelial tis ...

of the seminiferous epithelium. The protein was found throughout the Sertoli cell cytosol colocalized with microtubules. The 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 Tight junctions, also known as occluding junctions or ''zonulae occludentes'' (singular, ''zonula occludens''), are multiprotein Cell junction, junctional complexes between epithelial cells, sealing and preventing leakage of solutes and water. Th ...

. All of the microtubule-based tracks in Sertoli cells are crucial for the intracellular transport of organelles. CAMSAP2 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 the tracks could support

spermatogenesis Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testicle. This process starts with the Mitosis, mitotic division of the stem cells located close to the basement membrane of ...

and BTB dynamics. In a model of Sertoli cell injury, a 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 Microfilaments, also called actin filaments, are protein filaments in the cytoplasm of eukaryotic cells that form part of the cytoskeleton. They are primarily composed of polymers of actin, but are modified by and interact with numerous other p ...

caused by the injury, enabling proper distribution of BTB-associated proteins at the cell junctions.

Clinical research

Hepatocellular carcinoma (HCC)

CAMSAP2 plays a 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 the 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 Transcription factor Jun is a protein that in humans is encoded by the ''JUN'' gene. c-Jun, in combination with protein c-Fos, forms the AP-1 early response transcription factor. It was first identified as the Fos-binding protein p39 and only l ...

transrepression of HDAC6 along the Trio-dependent

Rac1 Ras-related C3 botulinum toxin substrate 1, is a protein that in humans is encoded by the ''RAC1'' gene. This gene can produce a variety of alternatively spliced versions of the Rac1 protein, which appear to carry out different functions. Func ...

JNK c-Jun N-terminal kinases (JNKs), were originally identified as kinases that bind and phosphorylate c-Jun on Ser-63 and Ser-73 within its transcriptional activation domain. They belong to the mitogen-activated protein kinase family, and are r ...

pathway, inhibiting CAMSAP2-mediated HCC

metastasis Metastasis is a pathogenic agent's spreading 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, ...

Colorectal cancer

CAMSAP2 promotes the migration of colorectal cancer cells by activating the

/ MMP-1 signaling pathway. Acting as an

oncogene An oncogene is a gene that has the potential to cause cancer. In tumor cells, these genes are often mutated, or expressed at high levels.

, CAMSAP2 promotes the capabilities of migration in colorectal cells. Through the silencing of the gene, the substantial downstream target, MMP-1, regulated the invasion of the cells and slowed down disease progress. Metastasis of colorectal cancer permeates through the activation of the signaling pathway and indicates CAMSAP2 as a promising target for treating metastatic colorectal cancer patients.

Gastric cancer

An association between CAMSAP2 expression levels and the progression and prognosis of gastric cancer was investigated in 2023. The investigation into the expression of the CAMSAP2 protein in gastric cancer aimed to understand its effects on cell invasion and

. One hundred six cancer patients underwent a radical

gastrectomy A gastrectomy is a partial or total surgical removal of the stomach. Indications Gastrectomies are performed to treat stomach cancer and perforations of the stomach wall. For severe duodenal ulcers, it may be necessary to remove the lower ...

, 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 Orthotopic procedures (from Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assu ...

gastric cancer cell

xenografts Xenotransplantation (''xenos-'' from the Greek meaning "foreign" or strange), or heterologous transplant, is the transplantation of living cells, tissues or organs from one species to another.in vitro ''In vitro'' (meaning ''in glass'', or ''in the glass'') Research, studies are performed with Cell (biology), cells or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in ...

results. The scientists discovered that gastric cancer tissues demonstrated high levels of CAMSAP2. The results positively correlated with

tumor markers A tumor marker is a Biomarker (medicine), biomarker that can be used to indicate the presence of cancer or the behavior of cancers (measure progression or response to therapy). They can be found in Body fluid, bodily fluids or Tissue (biology), ti ...

carcinoembryonic antigen Carcinoembryonic antigen (CEA) describes a set of highly-related glycoproteins involved in cell adhesion. CEA is normally produced in gastrointestinal tissue during fetal development, but the production stops before birth. Consequently, CEA is us ...

and

CA19-9 Carbohydrate antigen 19-9 (CA19-9), also known as sialyl-LewisA, is a tetrasaccharide which is usually attached to O-glycans on the surface of cells. It is known to play a role in cell-to-cell recognition processes. It is also a tumor marker used ...

. Bioinformatics analysis suggested CAMSAP2 is involved in epithelial-mesenchymal transition and the

upregulation In biochemistry, in the biological context of organisms' regulation of gene expression and production of gene products, downregulation is the process by which a cell decreases the production and quantities of its cellular components, such as R ...

of TGF-β signaling. In the mouse model, CAMSAP2 overexpressing xenografts illustrated enhanced metastasis, increased

vimentin Vimentin is a structural protein that in humans is encoded by the ''VIM'' gene. Its name comes from the Latin ''vimentum'' which refers to an array of flexible rods. Vimentin is a Intermediate filament#Type III, type III intermediate filamen ...

and

N-cadherin Cadherin-2 also known as Neural cadherin (N-cadherin), is a protein that in humans is encoded by the ''CDH2'' gene. CDH2 has also been designated as CD325 (cluster of differentiation 325). Cadherin-2 is a transmembrane protein expressed in multi ...

, and decreased

E-cadherin Cadherin-1 or Epithelial cadherin (E-cadherin), is a protein that in humans is encoded by the ''CDH1'' gene (not to be confused with the APC/C activator protein CDH1). Mutations are correlated with Hereditary diffuse gastric cancer, gastric, Here ...

. The high expression of CAMSAP2 contributes to gastric cancer progression and poor prognosis by the upregulation of TGF-β signaling.