Structural Organization of the Retriever-CCC Endosomal Recycling Complex

The recycling of membrane proteins from endosomes to the cell surface is vital for cell signaling and survival. Retriever, a trimeric complex of VPS35L, VPS26C and VPS29, together with the CCC complex comprising CCDC22, CCDC93, and COMMD proteins, plays a crucial role in this process. The precise mechanisms underlying Retriever assembly and its interaction with CCC have remained elusive. Here, we present the first high-resolution structure of Retriever determined using cryogenic electron microscopy. The structure reveals a unique assembly mechanism, distinguishing it from its remotely related paralog, Retromer. By combining AlphaFold predictions and biochemical, cellular, and proteomic analyses, we further elucidate the structural organization of the entire Retriever-CCC complex and uncover how cancer-associated mutations disrupt complex formation and impair membrane protein homeostasis. These findings provide a fundamental framework for understanding the biological and pathological implications associated with Retriever-CCC-mediated endosomal recycling.

Structural Organization of the Retriever-CCC Endosomal Recycling Complex

The recycling of membrane proteins from endosomes to the cell surface is vital for cell signaling and survival. Retriever, a trimeric complex of VPS35L, VPS26C and VPS29, together with the CCC complex comprising CCDC22, CCDC93, and COMMD proteins, plays a crucial role in this process. The precise mechanisms underlying Retriever assembly and its interaction with CCC have remained elusive. Here, we present the first high-resolution structure of Retriever determined using cryogenic electron microscopy. The structure reveals a unique assembly mechanism, distinguishing it from its remotely related paralog, Retromer. By combining AlphaFold predictions and biochemical, cellular, and proteomic analyses, we further elucidate the structural organization of the entire Retriever-CCC complex and uncover how cancer-associated mutations disrupt complex formation and impair membrane protein homeostasis. These findings provide a fundamental framework for understanding the biological and pathological implications associated with Retriever-CCC-mediated endosomal recycling.

Structure of the endosomal Commander complex linked to Ritscher-Schinzel syndrome

The Commander complex is required for endosomal recycling of diverse transmembrane cargos and is mutated in Ritscher-Schinzel syndrome. It comprises two sub-assemblies: Retriever composed of VPS35L, VPS26C, and VPS29; and the CCC complex which contains twelve subunits: COMMD1-COMMD10 and the coiled-coil domain-containing (CCDC) proteins CCDC22 and CCDC93. Combining X-ray crystallography, electron cryomicroscopy, and in silico predictions, we have assembled a complete structural model of Commander. Retriever is distantly related to the endosomal Retromer complex but has unique features preventing the shared VPS29 subunit from interacting with Retromer-associated factors. The COMMD proteins form a distinctive hetero-decameric ring stabilized by extensive interactions with CCDC22 and CCDC93. These adopt a coiled-coil structure that connects the CCC and Retriever assemblies and recruits a 16th subunit, DENND10, to form the complete Commander complex. The structure allows mapping of disease-causing mutations and reveals the molecular features required for the function of this evolutionarily conserved trafficking machinery.

Delineating the CCDC22-related Ritscher-Schinzel syndrome phenotype in the original family

Pathogenic variants in CCDC22 were initially described in 2012 in a large Australian family with intellectual disability and were subsequently noted to cause a phenotype consistent with the previously described Ritscher-Schinzel syndrome (RSS). The phenotypes of the original family were not described in detail and remains limited phenotypic data reported in medical literature. We detail the phenotypes of the original family, including newly diagnosed family members. With these eight phenotypic descriptions, more than triple the number of individuals for whom detailed clinical information is available. In addition to typical facies, common phenotypic features included intellectual disability, congenital heart disease and posterior fossa malformations, postnatal short stature, ectodermal abnormalities, and digital anomalies as previously described. Spinal curvature and genital anomalies were seen in most patients, while gastrointestinal features and disturbed sleep were also recurrently seen. We propose a possible mechanism linking the familial variant to a diagnosis of sarcoidosis in one individual. Given the clinical and genetic heterogeneity of RSS, we suggest a dyadic naming convention.

Expansion of the CCDC22 associated Ritscher-Schinzel/3C syndrome and review of the literature: Should the minimal diagnostic criteria be revised?

The Ritscher-Schinzel syndrome (RTSCS) is a rare condition with craniofacial, cardiac and fossa posterior abnormalities. RTSCS is subdivided into Ritscher-Schinzel syndrome 1 (RTSCS1) caused by pathogenic variants in coiled-coil domain-containing protein 22 (CCDC22), and Ritscher-Schinzel syndrome 2 (RTSCS2) caused by pathogenic variants in WASH complex subunit 5 (WASHC5). CCDC22 is inherited in an X-linked recessive manner while WASHC5 is inherited in an autosomal recessive manner. Only 17 individuals with a molecular diagnosis are reported. In the past, the diagnosis of RTSCS was solely based on the clinical findings, and minimal diagnostic criteria has been proposed for the syndrome: Cardiac malformations (other than isolated patent ductus arteriosis), fossa posterior malformations, and certain dysmorphic features. However, those criteria are not present in all patients. We aim to further delineate the spectrum of CDCC22 associated RTSCS and present a novel patient with epileptic encephalopathy due to a presumed disease causing CCDC22 missense variant inherited from a healthy mother and grandmother. An affected maternal uncle had passed away at the age of 12 months and was thus unavailable for genetic testing. The proband and the maternal uncle had the typical facial dysmorphism associated with RTSCS, and they closely resembled previously published RTSCS2 patients with a molecular diagnosis. This suggests that RTSCS1 and RTSCS2 patients have a similar facial gestalt. We also review the literature on RTSCS, we explore potential differences and similarities between CCDC22 and W ASHC5 associated RTSCS and discuss the minimal diagnostic criteria.

Identification of a novel CCDC22 mutation in a patient with severe Epstein-Barr virus-associated hemophagocytic lymphohistiocytosis and aggressive natural killer cell leukemia

Aggressive natural killer cell leukemia (ANKL) is a rare neoplasm characterized by the systemic infiltration of Epstein-Barr virus (EBV)-associated NK cells, and rapidly progressive clinical course. We report the case of a 45-year-old man with intellectual disability who developed ANKL, and describe the identification of a novel genetic mutation of coiled-coil domain-containing 22 (CCDC22). He presented with persistent fever, severe pancytopenia, and hepatosplenomegary. Following bone marrow aspiration, numerous hemophagocytes were identified. High EBV viral load was detected in NK cells fractionation by qPCR. The initial diagnosis was EBV-related hemophagocytic lymphohistiocytosis (EBV-HLH). A combination of immunosuppressive drugs and chemotherapy was administered, but was unsuccessful in controlling the disease. Therefore, he was treated with HLA-matched related allogeneic hematopoietic stem cell transplantation. However, his condition deteriorated within 30 days, resulting in fatal outcome. Autopsy revealed many EBV-infected NK cells infiltrating major organs, consistent with ANKL. Furthermore, whole-exome sequencing identified a novel missense mutation of the CCDC22 gene (c.112G>A, p.V38M), responsible for X-linked intellectual disability (XLID). CCDC22 has been shown to play a role in NF-κB activation. Our case suggests that CCDC22 mutation might be implicated in pathogenesis of EBV-HLH and NK-cell neoplasms as well as XLID via possibly affecting NF-κB signaling.

CCDC22 gene polymorphism is associated with advanced stages of endometriosis in a sample of Brazilian women

PURPOSE

Based on the assumption that genetic factors are involved in the etiology of endometriosis, this study aimed to investigate the possibility of rs498679 (TLR4 gene), rs1799964 (TNF-α gene), rs3024496 (IL-10 gene), and rs2294021 (CCDC22 gene) polymorphisms being associated with the occurrence of this disease in a sample of Brazilian women.

METHODS

We conducted a case-control study with 100 women with histological confirmation of endometriosis (endometriosis group) and 100 women submitted to laparoscopy for benign disorders, in which the absence of endometriosis was confirmed (control group). All samples were genotyped by real-time PCR technique for rs498679, rs1799964, rs3024496, and rs2294021 polymorphisms.

RESULTS

No significant difference was observed in genotypic or allelic frequencies between control and endometriosis groups for rs498679 (TLR4 gene), rs1799964 (TNF-α gene), rs3024496 (IL-10 gene), neither when comparing endometriosis subgroups (I-II versus III-IV). On the other hand, significant difference between stages I-II and III-IV of the disease was found in genotypic and allelic frequencies for the rs2294021 (CCDC22 gene) SNP (p = 0.048 and p = 0.017, respectively).

CONCLUSION

Our results suggest that the rs2294021 (CCDC22 gene) polymorphism could be associated with increased susceptibility to endometriosis in Brazilian women when the allele C is present. In order to clarify this result, further studies should be conducted on a larger population.