CD2AP (CD2 associated protein)

2017-11-01   Simona Panni 

DiBEST Department (Biologia, Ecologia, Scienze della Terra), via Pietro Bucci, Cubo 6C 87036 Arcavacata di Rende, CS (Italy).


Atlas Image
Chromosomal location of human CD2AP gene, according to NCBI. CD2AP gene is located on Chromosome 6, starting at 47477746 and ending at 47627263. The gene orientation is on the plus strand.


CD2AP gene encodes for an adaptor protein with high homology to Cin85. It was originally cloned as CD2 interacting protein and, in an independent study, as p130-Cas interacting protein. It contains three SH3 domains, a proline-rich motif and a coiled-coil domain that allow it to form complexes with numerous proteins and to participate in different physiological processes. Several evidences suggest that it links cell surface proteins and specialized junctions with the actin cytoskeleton and that it regulates the assembly of actin filaments to guide cell shape and movements.


Atlas Image
The longest transcript of CD2AP gene. It is 5412 bases long and consists of eighteen exons (represented as vertical bars) divided by 17 introns (represented as lines). Two short non coding regions at 5 and 3 complete the transcript. The length of each exon is reported (in number of bases).


The human CD2AP gene is located on chromosome 6p12, it is 149.517 bps long and comprises 18 exons (NCBI Gene ID: 23607, 2017)


The longest transcript is 5412 bases long, and comprises 18 exons. This transcript codes for the full lenght protein; four short transcripts (less than 700 bases) have been reported, but their functional role is unknown (Ensemble, Aug 2017). Two of these non-coding isoforms retain part of introns.




Atlas Image
Schematic representation of the CD2AP protein. Three SH3 domains occupy the amino terminal region of the protein (aa 1-330), followed by a short proline-rich motif (336-422). The carboxyl-terminal region contains an actin capping protein (CP) binding motif and a coiled-coil region (577-638) (Dikic 2002, Bruck et al. 2006).


CD2AP protein is an adaptor protein composed of several regions with binding functions: three SH3 domains, one proline rich region, four actin binding domains, AP-2 and CP binding motifs and a coiled-coil region. The protein is 639 aminoacids long and has a predicted molecular weight of 71,451 Dalton. The SH3 domains are located at the amino terminus of the protein and mediate complexes formation. Actually, SH3 domains are short modules of 60 amino acids commonly involved in the assembly and regulation of signalling processes by recognizing polyproline motifs, shaped in a left-handed type II helix, on the surface of the target proteins. In particular, CD2AP SH3 domains selectively recognize polyproline regions containing the consensus PXXXPR. One of this motif is contained in the p53 trascription factor, only in one of the two p53 polymorphic variants P72R, and allows the adaptor protein to selectively bind the 72 R variant (Panni et al. 2015). The crystal structure of two of the SH3 domains of CD2AP have been solved, showing that the domains conserve the typical beta-barrel shape, with five beta strands (Moncalian et al.2006; Yao et al. 2007). Two AP-2 binding motif (FXDXFX) overlap with the first and third SH3 domains respectively, while a third motif lies between the second and the third SH3 (Brett et al. 2002). Beyond these domains, the proline rich region (aa 336-422) contains motifs recognized by the SH3 domains of p130Cas, Src, Fyn, Yes and PI3K, all proteins involved in signal transduction (Kirsch et al. 1999, Dikic 2002). The presence of four putative actin binding sites (aa 534-538; 599-603; 610-614; 631-635) was observed in (Kirsch et al. 1999; Dikic 2002) and the direct binding of CD2AP to actin was shown in (Lehtonen et al. 2002), while the in vivo colocalization and co-immunoprecipitation of CD2AP with actin was demonstrated in (Yuan et al. 2002; Gaidos et al. 2007). Instead a CP (actin barbed-end capping protein) binding motif is present at amino acids 486-502 and mediates the binding of CD2AP to CP (which in turn binds to actin) and the resulting inhibition of the protective function of CP on actin filaments (Bruck et al. 2006; Takeda et al. 2010). The Carboxyl-terminal region adopts a coiled-coil conformation that allows the protein to homodimerise or heterodimerise with the homolog Cin85. (Kirsch et al. 1999, Gaidos et al. 2007)


CD2AP mRNA is ubiquitously expressed in human tissues (Kirsch et al. 1999). In particular, it is strongly expressed in the placenta, colon, kidney, pancreas and thymus, while a lower expression was detected in aorta, skeletal muscle, bladder and uterus (Kirsch et al. 1999).


CD2AP protein is localised mainly to the plasma membrane and to the cytosol
Atlas Image
CD2AP Interaction Network. The network was downloaded from the Intact Database (except for some nodes that were manually added) and visualized with Cytoscape (Orchard et al. 2014; Shannon et al. 2003). Both direct interactions and indirect associations of CD2AP are shown.


The presence of binding domains allows CD2AP to control the assembly of multiprotein complexes and to transmit signals involved in different biological processes. The protein was first identified as p130-Cas interactor (and named CMS as "Cas ligand with Multiple SH3") and its colocalization with p130-Cas and F-actin strongly suggested for a function in the regulation of the actin cytoskeleton as an adaptor protein (Kirsch et al. 1999). This role was largely confirmed by subsequent observations: in normal cells, monomeric actin (G actin) polymerises in filaments (F actin) that bind to CD2AP (Gaidos et al. 2007); in podocytes the absence of CD2AP causes a dramatic defect due to the loss of their specialised actin-rich foot processes that operate the filtration in kidney (Shih et al 1999 ; Gaidos et al. 2007). It was further shown that to guarantee stability to the actin polymer, its barbed ends are in complex with the actin-capping protein CP that avoid the addiction and the loss of monomers. In the presence of CD2AP, CP is prevented to bind actin filaments barbed end, and actin filaments can be extended or shortened (Bruck et al. 2006). Notably, CD2AP is required to recruit CP to the cell periphery during lamellipodia formation (Zhao et al. 2013) and to regulate actin accumulation at the adherens junctions (Tang and Brieher 2013). An independent work identified mouse CD2AP as CD2 receptor clustering activator in the specialized junctions between T cells and antigen-presenting cells (Dustin et al. 1998). This interaction also connects surface receptors to the actin cytoscheleton. A similar model was proposed in Drosophila, where Cindr, the CD2AP homolog, was shown to link cell-cell adhesion junctions with actin cytoscheleton by binding to E-Cadherin and IgCAM Roughest (Johnson et al. 2008; Johnson et al. 2012). It was also observed that upon EGF treatment CBL associates to CD2AP that recruits it to membrane ruffles where they both colocalize (Kirsch et al. 2001; Lynch et al. 2003), linking endocytosis to actin polymerization. RAC1 was found in membrane ruffles in complex with CTTN (cortactin) and CD2AP (Van Dujin et al. 2011). Recently it was suggested that the adaptor protein may anchor a fraction of the 72R variant of the TP53 protein in the cytosol, connecting it with membrane receptors and actin cytoscheleton (Panni et al. 2015). All these observations suggest for a role of CD2AP in regulating membrane proteins and specialized cell junctions and to connect them with actin cytoscheleton dynamics.
Atlas Image
The sequence alignment of the two homolog human proteins CD2AP and Cin85. The SH3 domains are highlighted in yellow and the proline-rich in green. Pink letters indicate the CP binding motif and the Coiled-Coil region. AP2 binding motifs are underlined and positions annotated as potential missense or nonsense mutations in Cosmic database (Forbes et al. 2017) are represented by red letters.


CD2AP is a member of the Cin85/CMS family of adaptor proteins which comprises two paralogs: CD2AP (CMS) and Cin85 (Figure 5) . They are conserved among mammalian species, but not in C. elegans and yeast. The D. melanogaster homolog, Cindr, only share 30% of homology with CD2AP (Blast Alignment tool



101 missense substitutions plus 8 nonsense substitutions mapping in the coding region of CD2AP gene have been annotated in the Cosmic Database (Forbes et al. 2017) from tumorigenic tissues analysis (positions involved are shown as red letters in Figure 5) , however none of them has been clearly associated with the tumorigenic tissue analysed. Mutation R612STOP was also found in one patient affected from focal segmental glomerulosclerosis (FSGS, see below) and it was shown that the mutation impairs gene expression (Lowik et al. 2007). 32 synonymous mutations have also been reported in Cosmic (not shown in the figure).
Two mutations of the splicing acceptor site of exon seven, that result in a lower expression of the gene, have been reported from FSGS patients (Kim et al. 2003).

Implicated in

Top note
CD2AP gene is clearly implicated in Focal Segmental Glomerulosclerosis, and its polymorphisms have been associated with Alzheimer Disease. Instead, although it was shown to interact with many proteins involved in signal transduction and with p53, its involvement in the development of cancer is not well documented. According to data provided by Human Protein Atlas and obtained with antibodies against CD2AP, the protein is strongly expressed in pancreatic, gastric, colorectal, prostate, breast, ovarian and urothelial cancers and in it is used as a prognostic marker in pancreatic cancer and urothelial cancer. It is a marker for plasmacytoid dendritic cell neoplasm too (see below).
It has been proposed as a promising target for ErbB2 overexpressing tumors since it participates in the inhibition of activated ErbB2 (Mineghishi et al. 2013).
Entity name
Focal Segmental Glomerulosclerosis
Mice CD2AP-/- die by 6-7 weeks of age for severe kidney pathology and proteinuria. In particular they showed glomerular injury with loss of podocyte foot processes and slit diaphragm integrity and with extracellular deposits of fibronectin and collagen (Shih et al. 1999). At molecular level, CD2AP immunoprecipitates with nephrin, the major component of the slit diaphragm (Shih et al. 1999 ; Shih et al. 2001), suggesting that the pathology arises from a deregulation of actin polymerisation in foot processes and loss of connection between nephrin and the actin cytoscheleton. Mice with CD2AP haploinsufficiency develop glomerular defects similar to the human focal segmental glomerulosclerosis disease, and in human patients mutations in CD2AP coding sequence or in the splicing regulatory regions were associated with the pathology (Kim et al. 2003; Lowik et al. 2007; Chen & Liapis, 2015)
Focal Segmental Glomerulosclerosis (FSGS) is a progressive glomerular disease characterized by localised sclerotic lesions (only some of the glomeruli are involved and only a part of them is affected) and podocyte loss. Glomerulus is a specialized apparatus to filter blood in kidney and the filtration barrier is constituted by endothelial cells, glomerular basement membrane and foot processes called podocytes (Shih et al. 1999). In FSGS patients, non functional podocytes are detached from the glomerular basement membrane which results in severe nephrosis with proteinuria and glomerulosclerosis (Nagata et al, 2017). Extracellular deposits of collagens and other fibrous proteins are also observed in affected glomeruli. 30% of all nephrotic syndromes in adults are due to FSGS with elevated costs to health care (Nagata et al. 2017).
Entity name
Alzheimer Disease
CD2AP polymorphisms were found associated with late onset Alzheimers disease (LOAD, see below) in two genome-wide association studies (Hollingworth et al. 2011; Naj et al. 2011). In particular, SNPs rs9296559 and rs9349407 were found associated with increased LOAD risk. Very little is known about how the protein may affect the AD risk and what function it exerts in brain. Its role in vescicular transport to the lysosome and in the formation of synapses may be relevant to its involvment (Karch & Goate, 2015). It was recently shown that CD2AP knock-down mice have a compromised blood-brain barrier with increased permeability, and the function of CD2AP in maintaining blood barrier integrity was proposed to be related with the higher predisposition to the disease (Cochran et al. 2015). It was also shown that the deletion of CD2AP determine a decrease in Aβ levels (Liao et al. 2015).
The Alzheimers Disease (AD) is a complex multifactorial neuronal disease characterized by extensive neuronal loss due to extracellular deposition of beta amyloid plaques (Aβ) and intracellular development of neurofibrillary tangles (NTF). AD is classified in late-onset AD (LOAD), that occurs in elderly people and is one of the most common cause of dementia, and early-onset AD (EOAD) when the disease occurs in young people (Rosenthal and Kamboh et al. 2014).
NAME Blastic Plasmacytoid Dendritic Cell Neoplasm (BPDCN)
CD2AP has been proposed as a specific marker to diagnostic BPDCN among other hematological neoplastic disorders because it is expressed at high level in both normal and transformed pDC cells. The molecular diagnosis of myeloproliferative disorders is based on markers such as CD4 or CD56 that are expressed in different cell types. Instead CD2AP, unless it was originally cloned in T cells, was shown to strongly react to specific antibodies only in pDC cells, suggesting that it may represent an interesting marker for pDC derived malignancies (Marafioti et al. 2008; Rizvi et al. 2012).
Blastic Plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematological malignancy involving plasmacytoid dendritic cells (pDC), that was classified in 2008 under acute myeloid leukemia (Riaz et al. 2014). It represents only 0.44% of the hematological malignancies however patients have poor outcomes, with median survival ranging from 12 to 16 months. Most patients present cutaneous lesions, while bone marrow, peripheral blood and lymph nodes are also involved (Riaz et al. 2014).


Pubmed IDLast YearTitleAuthors
120571952002Accessory protein recruitment motifs in clathrin-mediated endocytosis.Brett TJ et al
167075032006Identification of a novel inhibitory actin-capping protein binding motif in CD2-associated protein.Bruck S et al
261560922015Focal segmental glomerulosclerosis: molecular genetics and targeted therapies.Chen YM et al
263587792015The Alzheimer's disease risk factor CD2AP maintains blood-brain barrier integrity.Cochran JN et al
123546212002CIN85/CMS family of adaptor molecules.Dikic I et al
97416311998A novel adaptor protein orchestrates receptor patterning and cytoskeletal polarity in T-cell contacts.Dustin ML et al
278995782017COSMIC: somatic cancer genetics at high-resolution.Forbes SA et al
176069922007Structure and function analysis of the CMS/CIN85 protein family identifies actin-bundling properties and heterotypic-complex formation.Gaidos G et al
214608402011Common variants at ABCA7, MS4A6A/MS4A4E, EPHA1, CD33 and CD2AP are associated with Alzheimer's disease.Hollingworth P et al
230275492012Interactions between Drosophila IgCAM adhesion receptors and cindr, the Cd2ap/Cin85 ortholog.Johnson RI et al
249514552015Alzheimer's disease risk genes and mechanisms of disease pathogenesis.Karch CM et al
127641982003CD2-associated protein haploinsufficiency is linked to glomerular disease susceptibility.Kim JM et al
110678452001The adapter type protein CMS/CD2AP binds to the proto-oncogenic protein c-Cbl through a tyrosine phosphorylation-regulated Src homology 3 domain interaction.Kirsch KH et al
122178652002CD2-associated protein directly interacts with the actin cytoskeleton.Lehtonen S et al
258879562015Effects of CD2-associated protein deficiency on amyloid-β in neuroblastoma cells and in an APP transgenic mouse model.Liao F et al
177134652007Focal segmental glomerulosclerosis in a patient homozygous for a CD2AP mutation.Löwik MM et al
126728172003A Cortactin-CD2-associated protein (CD2AP) complex provides a novel link between epidermal growth factor receptor endocytosis and the actin cytoskeleton.Lynch DK et al
182188512008Novel markers of normal and neoplastic human plasmacytoid dendritic cells.Marafioti T et al
232795752013Adaptor protein complex of FRS2β and CIN85/CD2AP provides a novel mechanism for ErbB2/HER2 protein downregulation.Minegishi Y et al
170208802006Atypical polyproline recognition by the CMS N-terminal Src homology 3 domain.Moncalián G et al
286644082017Focal segmental glomerulosclerosis; why does it occur segmentally?Nagata M et al
214608412011Common variants at MS4A4/MS4A6E, CD2AP, CD33 and EPHA1 are associated with late-onset Alzheimer's disease.Naj AC et al
242344512014The MIntAct project--IntAct as a common curation platform for 11 molecular interaction databases.Orchard S et al
252615822015The adapter protein CD2AP binds to p53 protein in the cytoplasm and can discriminate its polymorphic variants P72R.Panni S et al
253102092014Blastic plasmacytoid dendritic cell neoplasm: update on molecular biology, diagnosis, and therapy.Riaz W et al
229535012012Expression of the CD2AP adaptor molecule in normal, reactive and neoplastic human tissue.Rizvi H et al
248298452014Late-Onset Alzheimer's Disease Genes and the Potentially Implicated Pathways.Rosenthal SL et al
145976582003Cytoscape: a software environment for integrated models of biomolecular interaction networks.Shannon P et al
117333792001CD2AP localizes to the slit diaphragm and binds to nephrin via a novel C-terminal domain.Shih NY et al
206255462010Two distinct mechanisms for actin capping protein regulation--steric and allosteric inhibition.Takeda S et al
243224282013FSGS3/CD2AP is a barbed-end capping protein that stabilizes actin and strengthens adherens junctions.Tang VW et al
171885872007Solution structure of the second SH3 domain of human CMS and a newly identified binding site at the C-terminus of c-Cbl.Yao B et al
119122542002Nephrin dissociates from actin, and its expression is reduced in early experimental membranous nephropathy.Yuan H et al
230909672013CD2AP links cortactin and capping protein at the cell periphery to facilitate formation of lamellipodia.Zhao J et al
204043452010Rac1 recruits the adapter protein CMS/CD2AP to cell-cell contacts.van Duijn TJ et al


Simona Panni

CD2AP (CD2 associated protein)

Atlas Genet Cytogenet Oncol Haematol. 2017-11-01

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