Marek Korzeniowski

Uniformed Services University of the Health Sciences | USUHS · Department of Medicine

The ER-resident proteins STIM1 together with the plasma membrane (PM)-localized Orai1 channels constitute the molecular components of the store-operated Ca²⁺ entry (SOCE) pathway. Prepositioning of STIM1 to the peripheral ER close to the PM ensures its efficient interaction with Orai1 upon a decrease in the ER luminal Ca²⁺ concentration. The C-term...

Mitochondria undergo coordinated rounds of fusion and fission that are critical for maintaining the functional integrity of this essential organelle. While a growing number of proteins have been identified as important regulators of mitochondrial dynamics, the direct role of membrane lipid composition during the fusion and fission processes is poor...

Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P 2 ) is a critically important regulatory lipid of the plasma membrane (PM); however, little is known about how cells regulate PM PI(4,5)P 2 levels. Here, we show that the phosphatidylinositol 4-phosphate (PI4P)/phosphatidylserine (PS) transfer activity of the endoplasmic reticulum (ER)–resident ORP5 a...

Decreased luminal ER Ca(2+) concentration triggers oligomerization and clustering of the ER Ca(2+)-sensor, STIM1 to promote its association with plasma membrane Orai1 Ca(2+) channels leading to increased Ca(2+) influx. A key step in STIM1 activation is the release of its SOAR domain from an intramolecular clamp formed with the STIM1 first coiled-co...

Oligomerization of the Ca(2+) sensor, STIM1, in the endoplasmic reticulum (ER) membrane, caused by depletion of ER Ca(2+) stores, results in STIM1 coupling to the plasma membrane Ca(2+) channel protein, Orai1, to activate Ca(2+) influx in a process known as store-operated Ca(2+) entry. We use fluorimetry-based fluorescence resonance energy transfer...

Polyunsaturated fatty acids (PUFAs) have been found to be effective inhibitors of cell signaling in numerous contexts, and we find that acute addition of micromolar PUFAs such as linoleic acid are effective inhibitors of Ca(2+)responses in mast cells stimulated by antigen-mediated crosslinking of FcεRI or by the SERCA pump inhibitor, thapsigargin....

Polyunsaturated fatty acids (PUFAs) have been found to be effective inhibitors of cell signaling in numerous contexts, and we find that acute addition of micromolar PUFAs such as linoleic acid are effective inhibitors of Ca2 + responses in mast cells stimulated by antigen-mediated crosslinking of FcεRI or by the SERCA pump inhibitor, thapsigargin....

Oligomerization of STIM1 and co-clustering with the Ca2+ channel protein, Orai1, at ER-plasma membrane (PM) junctions activates Ca2+ influx known as store-operated Ca2+ entry (SOCE) that is associated with visible puncta formed in the plane of the PM. Current information suggests that STIM1 in the resting state is minimally dimeric due to interacti...

Polyunsaturated fatty acids (PUFAs) have been found to be effective inhibitors of cell signaling in numerous contexts. We find that acute addition of these PUFAs in micromolar concentrations, including linoleic acid, substantially inhibits Ca2+ responses in mast cells stimulated by antigen-mediated crosslinking of FceRI or by the SERCA inhibitor, t...

The cytosolic level of Ca2+ has to be under tight control since Ca2+ is a potent regulator of many pivotal cellular functions. Store operated calcium entry (SOCE) is a major calcium entry mechanism present in virtually all cell types. Its activity is controlled by the luminal Ca2+ concentration of the ER. The stromal interaction molecule (STIM1) lo...

Stromal interaction molecule 1 (STIM1) stimulates calcium ion (Ca(2+)) entry through plasma membrane Orai1 channels in response to decreased Ca(2+) concentrations in the endoplasmic reticulum lumen. We identified an acidic motif within the STIM1 coiled-coil region that keeps its Ca(2+) activation domain [Ca(2+) release-activated Ca(2+) (CRAC) activ...

Calcium depletion of the endoplasmic reticulum (ER) induces oligomerisation, puncta formation and translocation of the ER Ca(2+) sensor proteins, STIM1 and -2 into plasma membrane (PM)-adjacent regions of the ER, where they activate the Orai1, -2 or -3 proteins present in the opposing PM. These proteins form ion channels through which store-operate...

Recent studies identified two main components of store-operated calcium entry (SOCE): the endoplasmic reticulum-localized Ca2+ sensor protein, STIM1, and the plasma membrane (PM)-localized Ca2+ channel, Orai1/CRACM1. In the present study, we investigated the phosphoinositide dependence of Orai1 channel activation in the PM and of STIM1 movements fr...

Receptor FcgammaIIA (FcgammaRIIA) associates with plasma membrane rafts upon activation to trigger signaling cascades leading to actin polymerization. We examined whether compartmentalization of PI(4,5)P(2) and PI(4,5)P(2)-synthesizing PIP5-kinase Ialpha to rafts contributes to FcgammaRIIA signaling. A fraction of PIP5-kinase Ialpha was detected in...

We studied an involvement of various cellular ceramide pools in signaling of immunoreceptor Fc gamma II (Fc gamma RII). The cell surface ceramide level was assessed by a technique based on binding of ceramide probes to intact cells. Total cellular ceramide was estimated by radioactive measurements. The activity of sphingomyelinases was measured by...

To reveal topography of FcgammaRII components of the receptor-signalling complex, large plasma-membrane sheets were obtained by cell cleavage and analysed by immuno-electron microscopy. Non-activated FcgammaRII was dispersed in the plane of the plasma membrane and only rarely was localized in the proximity of Lyn, an Src family tyrosine kinase, and...

Plasma membrane rafts are routinely isolated as detergent-resistant membranes (DRMs) floating in detergent-free density gradients. Here we show that both the presence and exclusion of TX-100 during the density gradient fractionation have profound effects on the location of FcgammaRII and TCR in DRM fractions. The presence of TX-100 during fractiona...