Deficiency of Anoctamin 5/TMEM16E causes nuclear positioning defect and impairs Ca2+ signaling of differentiated C2C12 myotubes

Ano5 deficiency disturbed bone formation by inducing osteoclast apoptosis in Gnathodiaphyseal dysplasia

Gnathodiaphyseal dysplasia (GDD) is a rare genetic syndrome characterized by cemento-ossifying fibroma lesions in the mandible and sclerosis of tubular bones. Currently, the clinical treatment of GDD is limited to surgical resection; therefore, novel treatment strategies developed through exploration of the related mechanisms are needed. Mutations in the TMEM16E/ANO5 gene are considered the main pathogenic factor of GDD, and the Ano5 knockout mouse model (Ano5-/-) established previously, which presented GDD-like characteristics, exhibited decreased osteoclastogenesis. ANO5, a calcium-activated chloride channel (CaCC), plays an important role in the maintenance of intracellular calcium homeostasis, which is crucial for osteoclast differentiation. In this study, our data indicated that the intracellular calcium concentration ([Ca2+]i) and calcium transients were significantly decreased in Ano5-/- osteoclasts accompanied by abnormally altered expression of calcium transporters, resulting in calcium dyshomeostasis. In addition, the endoplasmic reticulum stress (ERS) response was significantly enhanced in Ano5-/- osteoclasts, possibly because of calcium dyshomeostasis, which leading to the increased proportion of apoptotic osteoclasts via the activation of the C/EBP homologous protein (CHOP) signalling pathway, accompanied by abnormal changes in the expression of apoptosis-related factors. In summary, Ano5 deficiency impairs the function of osteoclasts by increasing osteoclast apoptosis, which is induced by an overactivated ERS response via calcium dyshomeostasis.

Anoctamin 5 promotes osteosarcoma development by increasing degradation of Nel-like proteins 1 and 2

Anoctamin 5 (ANO5) is a member of the Anoctamin (ANO) family of calcium-activated chloride channels. Although ANO5 expression is upregulated in various cancers, its role in osteosarcoma remains largely unknown. In this study, bioinformatics analysis, western blot, and immunohistochemical staining revealed that ANO5 was upregulated in osteosarcoma cell lines and osteosarcoma tissues, and ANO5 expression was positively associated with tumor size, tumor grade, and metastasis. Functional experiments demonstrated that inhibition of ANO5 decreased, while ANO5 overexpression increased, osteosarcoma cell proliferation and mobility in vitro. Immunoprecipitation, western blot, and confocal microscopy experiments showed that ANO5 bound to and promoted the degradation of Nel-like proteins 1 (NELL1) and 2 (NELL2). Moreover, a subcutaneous tumor transplantation model revealed that ANO5 knockdown reduced osteosarcoma cell proliferation and increased NELL1 and NELL2 expression in vivo. Finally, rescue experiments showed that knockdown of NELL1 or NELL2 reversed the inhibitory effects of ANO5 knockdown on osteosarcoma cell proliferation and migration. These results demonstrated that upregulation of ANO5 promoted osteosarcoma development by decreasing the stability of the NELL1 and NELL2 proteins and that ANO5 may be an effective target for the treatment of osteosarcoma.

ANO5 ensures trafficking of annexins in wounded myofibers

Mutations in ANO5 (TMEM16E) cause limb-girdle muscular dystrophy R12. Defective plasma membrane repair is a likely mechanism. Using myofibers from Ano5 knockout mice, we show that trafficking of several annexin proteins, which together form a cap at the site of injury, is altered upon loss of ANO5. Annexin A2 accumulates at the wound to nearly twice the level observed in WT fibers, while annexin A6 accumulation is substantially inhibited in the absence of ANO5. Appearance of annexins A1 and A5 at the cap is likewise diminished in the Ano5 knockout. These changes are correlated with an alteration in annexin repair cap fine structure and shedding of annexin-positive vesicles. We conclude that loss of annexin coordination during repair is disrupted in Ano5 knockout mice and underlies the defective repair phenotype. Although ANO5 is a phospholipid scramblase, abnormal repair is rescued by overexpression of a scramblase-defective ANO5 mutant, suggesting a novel, scramblase-independent role of ANO5 in repair.

TMEM16E/ANO5 mutations related to bone dysplasia or muscular dystrophy cause opposite effects on lipid scrambling

Mutations in the human TMEM16E/ANO5 gene are causative for gnathodiaphyseal dysplasia (GDD), a rare bone malformation and fragility disorder, and for two types of muscular dystrophy (MD). Previous studies have demonstrated that TMEM16E/ANO5 is a Ca²⁺ -activated phospholipid scramblase and that the mutation c.1538C>T (p.Thr513Ile) causing GDD leads to a gain-of-function phenotype. Here, using established HEK293-based functional assays, we investigated the effects of MD-related and further GDD-related amino acid exchanges on TMEM16E/ANO5 function in the same expression system. These experiments also revealed that the gradual changes in HEK293 cell morphology observed upon expression of TMEM16E/ANO5^GDD mutants are a consequence of aberrant protein activity. Our results collectively demonstrate that, on the level of protein function, MD mutations are associated to loss-of-function and GDD mutations to gain-of-function phenotypes, confirming conjectures made on the basis of inheritance modes.