Signaling through the store-operated Ca 2+ release-activated Ca 2+ (CRAC) channel regulates critical cellular functions, including gene expression, cell growth and differentiation, and Ca 2+ homeostasis. Loss-of-function mutations in the CRAC channel pore-forming protein ORAI1 or the Ca 2+ sensing protein stromal interaction molecule 1 (STIM1) result in severe immune dysfunction and nonprogressive myopathy. Here, we identify gain-of-function mutations in the cytoplasmic domain of STIM1 (p.R304W) associated with thrombocytopenia, bleeding diathesis, miosis, and tubular myopathy in patients with Stormorken syndrome, and in ORAI1 (p.P245L), associated with a Stormorken-like syndrome of congenital miosis and tubular aggregate myopathy but without hematological abnormalities. Heterologous expression of STIM1 p.R304W results in constitutive activation of the CRAC channel in vitro, and spontaneous bleeding accompanied by reduced numbers of thrombocytes in zebrafish embryos, recapitulating key aspects of Stormorken syndrome. p.P245L in ORAI1 does not make a constitutively active CRAC channel, but suppresses the slow Ca 2+ -dependent inactivation of the CRAC channel, thus also functioning as a gain-of-function mutation. These data expand our understanding of the phenotypic spectrum of dysregulated CRAC channel signaling, advance our knowledge of the molecular function of the CRAC channel, and suggest new therapies aiming at attenuating store-operated Ca 2+ entry in the treatment of patients with Stormorken syndrome and related pathologic conditions. human genetics | calcium signaling C a 2+ influx in response to the depletion of intracellular Ca 2+ stores, or store-operated Ca 2+ entry, constitutes one of the major routes of Ca 2+ entry in all animal cells (1). Under physiological conditions, Ca 2+ influx is activated in response to numerous G protein-coupled receptors and receptor tyrosine kinases signaling via inositol-1,4,5-trisphosphate as a second messenger (2). Store-operated Ca 2+ entry is mediated primarily by the Ca 2+ release-activated Ca 2+ (CRAC) channel (3), which consists of the pore-forming subunits ORAI1-3 (or CRAC modulators 1-3) and Ca 2+ sensors, STIM1 and STIM2 (4-7). STIM proteins reside in the membrane of endoplasmic reticulum (ER), whereas ORAI proteins reside in the plasma membrane. STIM1 is a single transmembrane-spanning protein (8-12) that, in resting cells, exists as a dimer that binds Ca 2+ through two EF hand-containing domains located in the ER lumen (13). Depletion of Ca 2+ in the ER induces a series of molecular events in the conformation and localization of STIM1, initiated by the formation of higher-order oligomers, protein unfolding, and accumulation at discrete sites in the cell where the ER membrane is in close proximity to the plasma membrane (11,(13)(14)(15)(16). In these sites, STIM1 binds to the cytosolic C and N termini of ORAI1 (17, 18), resulting in channel activation and generation of a highly Ca 2+ -selective CRAC current, or I CRAC (3,19,20). I CRAC is responsible not only ...

Primary cilia start forming within the G1 phase of the cell cycle and continue to grow as cells exit the cell cycle (G0). They start resorbing when cells re-enter the cell cycle (S phase) and are practically invisible in mitosis. The mechanisms by which cilium biogenesis and disassembly are coupled to the cell cycle are complex and not well understood. We previously identified the centrosomal phosphoprotein NDE1 as a negative regulator of ciliary length and showed that its levels inversely correlate with ciliogenesis. Here, we identify the tumor suppressor FBW7 (also known as FBXW7, CDC4, AGO, or SEL-10) as the E3 ligase that mediates the destruction of NDE1 upon entry into G1. CDK5, a kinase active in G1/G0, primes NDE1 for FBW7-mediated recognition. Cells depleted of FBW7 or CDK5 show enhanced levels of NDE1 and a reduction in ciliary length, which is corrected in cells depleted of both FBW7 or CDK5 and NDE1. These data show that cell cycle-dependent mechanisms can control ciliary length through a CDK5-FBW7-NDE1 pathway.

Background: Ca 2ϩ signaling is essential for osteoclastogenesis. Results: I-mfa negatively regulates TRPC1-mediated Ca 2ϩ signaling and osteoclastogenesis. Conclusion: TRPC1 and I-mfa fine-tune the dynamic range of store-operated Ca 2ϩ entry channels during osteoclastogenesis. Significance: The TRPC1/I-mfa interaction is biologically relevant in osteoclastogenesis.

Naturally occurring mutations in two separate, but interacting loci, pkd1 and pkd2 are responsible for almost all cases of autosomal dominant polycystic kidney disease (ADPKD). ADPKD is one of the most common genetic diseases resulting primarily in the formation of large kidney, liver, and pancreatic cysts. Homozygous deletion of either pkd1 or pkd2 results in embryonic lethality in mice due to kidney and heart defects illustrating their indispensable roles in mammalian development. However, the mechanism by which mutations in these genes cause ADPKD and other developmental defects are unknown. Research in the past several years has revealed that PKD2 has multiple functions depending on its subcellular localization. It forms a receptor-operated, non-selective cation channel in the plasma membrane, a novel intracellular Ca 2+ release channel in the endoplasmic reticulum (ER), and a mechanosensitive channel in the primary cilium. This review focuses on the functional compartmentalization of PKD2, its modes of activation, and PKD2-mediated signal transduction.

OBJECTIVE The chromatin remodeling enzyme BRG1 transcriptionally regulates target genes important for early blood vessel development and primitive hematopoiesis. However, because Brg1 deletion in vascular progenitor cells results in lethal anemia by embryonic day 10.5 (E10.5), roles for BRG1 in embryonic vascular development after midgestation are unknown. In this study, we sought to determine whether endothelial cell BRG1 regulates genes important for vascular development or maintenance later in embryonic development. APPROACH AND RESULTS Using mice with temporally inducible deletion of endothelial BRG1 (Brg1fl/fl;Cdh5(PAC)-CreERT2), we found Brg1 excision between E9.5–11.5 results in capillary dilation and lethal hemorrhage by E14.5. This phenotype strongly resembles that seen when the serum response factor (SRF) transcription factor is deleted from embryonic endothelial cells. Although expression of Srf and several of its known endothelial cell target genes are downregulated in BRG1-depleted endothelial cells, we did not detect binding of BRG1 at these gene promoters, indicating that they are not direct BRG1 target genes. Instead, we found BRG1 binds to the promoters of the SRF cofactors myocardin-related transcription factors A and B (Mrtfa and Mrtfb) in endothelial cells, and these genes are downregulated in Brg1-deficient endothelial cells. CONCLUSIONS BRG1 promotes transcription of endothelial Mrtfa and Mrtfb, which elevates expression of SRF and SRF target genes that establish embryonic capillary integrity. These data highlight a new and temporally specific role for BRG1 in embryonic vasculature and provide novel information about epigenetic regulation of Mrtf expression and SRF signaling in developing blood vessels.