The cluster of differentiation (CD) system is commonly used as cell markers in immunophynotyping. Different kinds of cells in the immune system can be identified through the surface CD molecules which associating with the immune function of the cell. There are more than 320 CD unique clusters and subclusters have been identified. Some of the CD molecules serve as receptors or ligands important to the cell through initiating a signal cascade which then alter the behavior of the cell. Some CD proteins do not take part in cell signal process but have other functions such as cell adhesion. The CD155 ligand CD96 is a member of the Ig superfamily. It's a immunoglobulin-like protein tentatively allocated to the repertoire of human NK receptors. NK cells recognize poliovirus receptor (PVR), a nectins and nectin-like protein family member serve to mediate cell-cell adhesion, cell migration, with the presence of an additional receptor, CD96. CD96 promotes NK cell adhesion to target cells expressing PVR, stimulates cytotoxicity of activated NK cells, and mediates acquisition of PVR from target cells. The effect the cells with mutated CD96 protein lost adhesion and growth activities indicates that CD96 mutations may cause a form of the C syndrome by interfering with cell adhesion and growth.
CD99 antigen-like protein 2, also known as MIC2-like protein 1, CD99L2 and MIC2L1, is a single-pass type I membrane protein which belongs to theCD99 family. CD99L2 is expressed in brain, heart, lung, liver, spleen, kidney, stomach, small intestine, skeletal muscle, ovary, thymus, testis and uterus. Lower expression of CD99L2 is seen in thymus. It is also expressed in E18 uterus and placenta. CD99 and CD99L2 were required for leukocyte extravasation in the cremaster after stimulation with tumor necrosis factor-alpha, where the need for PECAM-1 is known to be bypassed. CD99 and CD99L2 act independently of PECAM-1 in leukocyte extravasation and cooperate in an independent way to help neutrophils overcome the endothelial basement membrane. CD99L2 may function as a homophilic adhesion molecule. It functions in leukocyte-endothelial cell interactions during leukocyte extravasation, and in particular, at the diapedesis step. CD99L2 does not seem to be involved in docking of leukocytes to the vessel wall or in lymphocyte diapedesis.
The cluster of differentiation (CD) system is commonly used as cell markers in immunophynotyping. Different kinds of cells in the immune system can be identified through the surface CD molecules which associating with the immune function of the cell. There are more than 320 CD unique clusters and subclusters have been identified. Some of the CD molecules serve as receptors or ligands important to the cell through initiating a signal cascade which then alter the behavior of the cell. Some CD proteins do not take part in cell signal process but have other functions such as cell adhesion. CD99 is a transmembrane protein expressed on most hematopoietic cells, endothelial cells and at the borders between confluent cells. CD99 is also found expressed in the development of normal ovary and testis as well as in 25 sex cord-stromal tumors, 7 epithelial neoplasms, and 6 germ cell tumors. CD99 may be a useful marker for sex cord-stromal tumors and that its degree of reactivity correlates with the degree of differentiation in Sertoli-Leydig cell tumors. Additionally, CD99 might aid in distinguishing granulose cell tumors of the ovary from poorly differentiated carcinomas and it has been reported to be a sensitive and specific marker for Ewing's sarcoma and primitive neuroectodermal tumor.
CDC2, also known as CDK1, contains 1 protein kinase domain and belongs to the protein kinase superfamily, CMGC Ser/Thr protein kinase family, CDC2/CDKX subfamily. CDC2 is a catalytic subunit of the highly conserved protein kinase complex known as M-phase promoting factor (MPF), which is essential for G1/S and G2/M phase transitions of eukaryotic cell cycle. Mitotic cyclins stably associate with CDC2 and function as regulatory subunits. The kinase activity of CDK1 is controlled by cyclin accumulation and destruction through the cell cycle. The phosphorylation and dephosphorylation of CDC2 also play important regulatory roles in cell cycle control. It is required in higher cells for entry into S-phase and mitosis. CDC2 also is a cyclin-dependent kinase which displays CTD kinase activity and is required for RNA splicing. It has CTD kinase activity by hyperphosphorylating the C-terminal heptapeptide repeat domain (CTD) of the largest RNA polymerase II subunit RPB1, thereby acting as a key regulator of transcription elongation. CDK1 is required for RNA splicing, possibly by phosphorylating SRSF1/SF2. It is involved in regulation of MAP kinase activity, possibly leading to affect the response to estrogn inhibitors.
CDC37 is a protein that is expressed in proliferative zones during embryonic development and in adult tissues, consistent with a positive role in proliferation and is required for cell division in budding yeast. CDC37 is though to play an important role in the establishment of signaling pathways controlling cell proliferation through targeting intrinsically unstable oncoprotein kinases such as Cdk-4, Raf-1, and src to the molecular chaperone Hsp90. Decreased Hsp90 expression can reduce the levels of microtubule-associated protein tau, whose overexpression may induce many diseases. CDC37 is considered as a co-chaperone that is classified to Hsp90's accessory proteins. It has been reported that suppression of Cdc37 destabilized tau, leading to its clearance, whereas cdc37 overexpression preserved tau.Cdc37 was found to co-localize with tau in neuronal cells and to physically interact with tau from human brain. Moreover, Cdc37 levels significantly increased with age.
CDCP1 contains three extracellular CUB domains. It is a putative stem cell marker that is highly expressed in some human cancer cells and in both, typical and atypical (cancerous) colons. It interacts with CDH2/N-cadherin, CDH3/P-cadherin, SDC1/syndecan-1, SDC4/syndecan-4 and the serine protease ST14/MT-SP1. It also interacts with SRC and PRKCG/protein kinase C gamma. CDCP1 is taken as a key regulator of EGF/EGFR-induced cell migration. It has been shown that signaling via EGF/EGFR induces migration of ovarian cancer Caov3 and OVCA420 cells with concomitant up-regulation of CDCP1 mRNA and protein. Consistent with a role in cell migration CDCP1 relocates from cell-cell junctions to punctate structures on filopodia after activation of EGFR. It may be involved in cell adhesion and cell matrix association. It also may play a role in the regulation of anchorage versus migration or proliferation versus differentiation via its phosphorylation. It has been taken as a novel marker for leukemia diagnosis and for immature hematopoietic stem cell subsets.
Cadherins (Calcium dependent adhesion molecules) are a class of transmembrane proteins. Cadherin-5, also known as VE-cadherin, CDH5 and CD144, an endothelial specific cell-cell adhesion molecule, plays a pivotal role in the formation, maturation and remodeling of the vascular wall. VE-Cadherin is widely considered to be specific for vascular endothelia in which it is either the sole or the predominant cadherin, often co-existing with N-cadherin. This specificity of VE-cadherin for vascular endothelial cells is important not only in blood and lymph vessel biology and medicine, but also for cell-type-based diagnoses, notably those of metastatic tumors. As a classical cadherin, VE-Cadherin links endothelial cells together by homophilic interactions mediated by its extracellular part and associates intracellularly with the actin cytoskeleton via catenins. Mechanisms that regulate VE-cadherin-mediated adhesion are important for the control of vascular permeability and leukocyte extravasation. In addition to its adhesive functions, VE-Cadherin regulates various cellular processes such as cell proliferation and apoptosis and modulates vascular endothelial growth factor receptor functions. Consequently, VE-cadherin is essential during embryonic angiogenesis.
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