Modulation of Calcium Entry by Mitochondria.

The role of mitochondria in intracellular Ca(2+) signaling relies mainly in its capacity to take up Ca(2+) from the cytosol and thus modulate the cytosolic [Ca(2+)]. Because of the low Ca(2+)-affinity of the mitochondrial Ca(2+)-uptake system, this organelle appears specially adapted to take up Ca(2+) from local high-Ca(2+) microdomains and not from the bulk cytosol. Mitochondria would then act as local Ca(2+) buffers in cellular regions where high-Ca(2+) microdomains form, that is, mainly close to the cytosolic mouth of Ca(2+) channels, both in the plasma membrane and in the endoplasmic reticulum (ER).

Functional roles of MICU1 and MICU2 in mitochondrial Ca(2+) uptake.

MICU1 and MICU2 are the main regulators of the mitochondrial Ca(2+)-uniporter (MCU), but their precise functional role is still under debate. We show here that MICU2 behaves as a pure inhibitor of MCU at low cytosolic [Ca(2+)] ([Ca(2+)]c), though its effects decrease as [Ca(2+)]c is increased and disappear above 7 μM. Regarding MICU1, studying its effects is more difficult because knockdown of MICU1 leads also to loss of MICU2.

Dynamics of mitochondrial Ca2+ uptake in MICU1-knockdown cells.

MICU1 (Ca2+ uptake protein 1, mitochondrial) is an important regulator of the MCU (Ca2+ uniporter protein, mitochondrial) that has been shown recently to act as a gatekeeper of the MCU at low [Ca2+]c (cytosolic [Ca2+]). In the present study we have investigated in detail the dynamics of MCU activity after shRNA-knockdown of MICU1 and we have found several new interesting properties. In MICU1-knockdown cells, the rate of mitochondrial Ca2+ uptake was largely increased at a low [Ca2+]c (<2 μM), but it was decreased at a high [Ca2+]c (>4 μM).

Expression profiles of novel cell surface molecules on B-cell subsets and plasma cells as analyzed by flow cytometry.

Cell surface molecules are present on several lymphocyte subsets and are differentially expressed during lymphocyte development and activation. Human Leukocyte Differentiation Antigen (HLDA) Workshops have played an essential role in the identification and characterization of the molecules found in the membrane of hematopoietic cells. In the present study, the reactivities of sixty-five monoclonal antibodies (mAbs) submitted to the HLDA9 Workshop were tested.

Expression of SLAM (CD150) cell-surface receptors on human B-cell subsets: from pro-B to plasma cells.

The SLAM (CD150) family receptors are leukocyte cell-surface glycoproteins involved in leukocyte activation. These molecules and their adaptor protein SAP contribute to the effective germinal center formation, generation of high-affinity antibody-secreting plasma cells, and memory B cells, thereby facilitating long-term humoral immune response. Multi-color flow cytometric analysis was performed to determine the expression of CD48 (SLAMF2), CD84 (SLAMF5), CD150 (SLAM or SLAMF1), CD229 (Ly9 or SLAMF3), CD244 (2B4 or SLAMF4), CD319 (CRACC, CS1, or SLAMF7), and CD352 (NTB-A or SLAMF6) on human cell lines and B-cell subsets.

New B-cell CD molecules.

B cells not only play a pivotal role in humoral immunity, but also are involved in a broad spectrum of immune responses, including antigen presentation and T-cell function regulation. The identification of cell-surface CD molecules derived from a series of Human Leukocyte Differentiation Antigens (HLDA) Workshops has been instrumental to the discovery and functional characterization of human B-cell populations. Moreover, many events regulating B-cell development, activation, and effector functions are orchestrated by these cell-surface molecules.