Search

Calcium (Ca(2+)) is a critical cofactor and signaling mediator in cells, and the concentration of cytosolic Ca(2+) is regulated by multiple proteins, including the plasma membrane Ca(2+)-ATPases (adenosine triphosphatases) (PMCAs), which use ATP to transport Ca(2+) out of cells. PMCA isoforms exhibit different kinetic and regulatory properties; thus, the presence and relative abundance of individual isoforms may help shape Ca(2+) transients and cellular responses. We studied the effects of three PMCA isoforms (PMCA4a, PMCA4b, and PMCA2b) on Ca(2+) transients elicited by conditions that trigger store-operated Ca(2+) entry (SOCE) and that blocked Ca(2+) uptake into the endoplasmic reticulum in HeLa cells, human embryonic kidney (HEK) 293 cells, or primary endothelial cell isolated from human umbilical cord veins (HUVECs). The slowly activating PMCA4b isoform produced long-lasting Ca(2+) oscillations in response to SOCE. The fast-activating isoforms PMCA2b and PMCA4a produced different effects. PMCA2b resulted in rapid and highly PMCA abundance-sensitive clearance of SOCE-mediated Ca(2+) transients, whereas PMCA4a reduced cytosolic Ca(2+), resulting in the establishment of a higher than baseline cytosolic Ca(2+) concentration. Mathematical modeling showed that slow activation was critical to the sustained oscillation induced by the "slow" PMCA4b pump. The modeling and experimental results indicated that the distinct properties of PMCA isoforms differentially regulate the pattern of SOCE-mediated Ca(2+) transients, which would thus affect the activation of downstream signaling pathways., (Copyright © 2015, American Association for the Advancement of Science.)

Schnitzler syndrome is considered to be a rare disorder characterized by a monoclonal IgM protein and chronic urticaria that is associated with considerable morbidity. We hypothesized that the syndrome may be under-recognized and patients may be deprived of highly effective therapy in the form of anakinra. We performed a retrospective search of the dysproteinemia database at Mayo Clinic as well as the medical records of all patients with chronic urticaria to determine the true incidence of the disease. We compared patients with the diagnosis of Schnitzler syndrome and those who met the criteria but in whom the syndrome was not recognized. Comparisons between groups were performed and survival curves determined. We identified 16 patients with diagnosed Schnitzler syndrome and an additional 46 patients who met diagnostic criteria. The monoclonal protein was IgMκ in 94% of patients. Therapy with anakinra in 4 patients led to rapid and complete resolution of symptoms. The median overall survival for this syndrome is over 12.8 years. Progression to lymphoma was only observed in 8% of patients; this is lower than previous reports. Schnitzler syndrome may be present in up to 1.5% of patients with a monoclonal IgM in their serum and likely under-recognized as a clinical syndrome.