The key proteins mediating store-operated Ca 2+ entry (SOCE) are the endoplasmic reticulum (ER) Ca 2+ sensor STIM1 and the plasma membrane Ca 2+ -selective channel Orai1. Here, we quantitatively dissect Orai1 trafficking dynamics and show that Orai1 recycles rapidly at the plasma membrane (K ex ≃0.1 min −1

Endoplasmic reticulum (ER) stress contributes to acute kidney injury induced by several causes. Kidney dysfunction was shown to be influenced by gender differences. In this study we observed differences in the severity of kidney injury between male and female mice in response to tunicamycin, an ER stress agent. Tunicamycin-treated male mice showed a severe decline in kidney function and extensive kidney damage of proximal tubules in the kidney outer cortex (S1 and S2 segments). Interestingly, female tunicamycin-treated mice did not show a decline in kidney function, and their kidneys showed damage localized primarily to proximal tubules in the inner cortex (S3 segment). Protein markers of ER stress, glucose-regulated protein, and X-box binding protein 1 were also more elevated in male mice. Similarly, the induction of apoptosis was higher in tunicamycin-treated male mice, as measured by the activation of Bax and caspase-3. Testosterone administered to female mice before tunicamycin resulted in a phenotype similar to male mice with a comparable decline in renal function, tissue morphology, and induction of ER stress markers. We conclude that kidneys of male mice are much more susceptible to ER stress-induced acute kidney injury than those of females. Moreover, this sexual dimorphism could provide an interesting model to study the relation between kidney function and injury to a specific nephron segment.

Siglecs (Sialic acid-binding immunoglobulin-type lectins) are a I-type lectin that typically binds sialic acid. Siglecs are predominantly expressed in immune cells and generate activating or inhibitory signals. They are also shown to be expressed on the surface of cells in the nervous system and have been shown to play central roles in neuroinflammation. There has been a plethora of reviews outlining the studies pertaining to Siglecs in immune cells. However, this review aims to compile the articles on the role of Siglecs in brain function and neurological disorders. In humans, the most abundant Siglecs are CD33 (Siglec-3), Siglec-4 (myelin-associated glycoprotein/MAG), and Siglec-11, Whereas in mice the most abundant are Siglec-1 (sialoadhesin), Siglec-2 (CD22), Siglec-E, Siglec-F, and Siglec-H. This review is divided into three parts. Firstly, we discuss the general biological aspects of Siglecs that are expressed in nervous tissue. Secondly, we discuss about the role of Siglecs in brain function and molecular mechanism for their function. Finally, we collate the available information on Siglecs and neurological disorders. It is intriguing to study this family of proteins in neurological disorders because they carry immunoinhibitory and immunoactivating motifs that can be vital in neuroinflammation.

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A chaperone complex (CCT) regulates the trafficking of a calcium channel (Orai1) and, as such, modulates cellular function.

Vertebrate oocytes are maintained in meiotic arrest for prolonged periods of time before undergoing oocyte maturation in preparation for fertilization. Cyclic AMP (cAMP) signaling plays a crucial role in maintaining meiotic arrest, which is released by a species-specific hormonal signal. Evidence in both frog and mouse argues that meiotic arrest is maintained by a constitutively active G-protein coupled receptor (GPCR) leading to high cAMP levels. Because activated GPCRs are typically targeted for endocytosis as part of the signal desensitization pathway, we were interested in determining the role of trafficking at the cell membrane in maintaining meiotic arrest. Here we show that blocking exocytosis, using a dominant-negative SNAP25 mutant in Xenopus oocytes, releases meiotic arrest independently of progesterone. Oocyte maturation in response to the exocytic block induces the MAPK and Cdc25C signaling cascades, leading to MPF activation, germinal vesicle breakdown and arrest at metaphase of meiosis II with a normal bipolar spindle. It thus replicates all tested aspects of physiological maturation. Furthermore, inhibiting clathrin-mediated endocytosis hinders the effectiveness of progesterone in releasing meiotic arrest. These data show that vesicular traffic at the cell membrane is crucial in maintaining meiotic arrest in vertebrates, and support the argument for active recycling of a constitutively active GPCR at the cell membrane.

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Hodeify R, Tarcsafalvi A, Megyesi J, Safirstein RL, Price PM. Cdk2-dependent phosphorylation of p21 regulates the role of Cdk2 in cisplatin cytotoxicity. Am J Physiol Renal Physiol 300: F1171-F1179, 2011. First published February 16, 2011 doi:10.1152/ajprenal.00507.2010.-Cisplatin cytotoxicity is dependent on cyclin-dependent kinase 2 (Cdk2) activity in vivo and in vitro. We found that an 18-kDa protein identified by mass spectrometry as p21 WAF1/Cip1 was phosphorylated by Cdk2 starting 12 h after cisplatin exposure. The analysis showed it was phosphorylated at serine 78, a site not previously identified. The adenoviral transduction of p21 before cisplatin exposure protects from cytotoxicity by inhibiting Cdk2. Although cisplatin causes induction of endogenous p21, the protection is inefficient. We hypothesized that phosphorylation of p21 at serine 78 could affect its role as a Cdk inhibitor, and thereby lessen its ability to protect from cisplatin cytotoxicity. To investigate the effect of serine 78 phosphorylation on p21 activity, we replaced serine 78 with aspartic acid, creating the phosphomimic p21 S78D . Mutant p21 S78D was an inefficient inhibitor of Cdk2 and was inefficient at protecting TKPTS cells from cisplatininduced cell death. We conclude that phosphorylation of p21 by Cdk2 limits the effectiveness of p21 to inhibit Cdk2, which is the mechanism for continued cisplatin cytotoxicity even after the induction of a protective protein.cell death CISPLATIN IS A CHEMOTHERAPEUTIC drug used as a first-line component in the treatment of several solid tumors, including testicular, head and neck, and ovarian and cervical cancers (14). Its dosage and efficacy are limited by its side effects, especially nephrotoxicity (39). Cisplatin cytotoxicity in kidney cells is dependent on cyclin-dependent kinase 2 (Cdk2) activity in vivo and in vitro (42,43). This dependence was shown by Cdk2 inhibitory drugs, dominant-negative Cdk2 transduction, and expression of the cyclin-dependent kinase inhibitor (CDKI), p21, all of which protected from cisplatininduced cell death. Cdk2 is a serine/threonine protein kinase, whose main described function is the phosphorylation of substrates necessary for cell cycle progression (37). The Cdk2 pathways involved in cisplatin-induced cell death are not yet understood, and one substrate in these pathways is described below.Cdk2 activity is regulated by several mechanisms, including binding to cyclins, positive and negative phosphorylation, and binding of CDKIs (38). Apart from its role in cell cycle progression, various studies showed increased Cdk2 activity associated with programmed cell death (apoptosis) (21,36,43,45,54,65,66), and inhibition of Cdk2 activity in vitro has been shown to protect cultured cells from apoptosis (40,42,43,61).In the present study, we identified a Cdk2 substrate induced after cisplatin exposure. An 18-kDa protein accumulated and was phosphorylated by Cdk2 starting 12 h after cisplatin exposure, which coincided with the time when Cdk2 inhibition no longer protec...