Abstract
T lymphocytes enlarge (blast) and proliferate in response to antigens in a multistep program that involves obligatory cytosolic calcium elevations. Store-operated calcium entry (SOCE) pathway is the primary source of Ca2+ in these cells. Here, we describe a novel modulator of blastogenesis, proliferation and SOCE: the TRPM7 channel kinase. TRPM7 kinase-dead (KD) K1646R knock-in mice exhibited splenomegaly and impaired blastogenic responses elicited by PMA/ionomycin or anti-CD3/CD28 antibodies. Splenic T-cell proliferation in vitro was weaker in the mutant compared to wildtype littermates. TRPM7 current magnitudes in WT and KD mouse T cells were, however, similar. We tested the dependence of T-cell proliferation on external Ca2+ and Mg2+ concentrations. At a fixed [Mg2+o] of ~0.4 mM, Ca2+o stimulated proliferation with a steep concentration dependence and vice versa, at a fixed [Ca2+o] of ~0.4 mM, Mg2+o positively regulated proliferation but with a shallower dependence. Proliferation was significantly lower in KD mouse than in wildtype at all Ca2+ and Mg2+ concentrations. Ca2+ elevations elicited by anti-CD3 antibody were diminished in KD mutant T cells and SOCE measured in activated KD splenocytes was reduced. These results demonstrate that a functional TRPM7 kinase supports robust SOCE, blastogenesis and proliferation, whereas its inactivation suppresses these cellular events.
Highlights
IntroductionCa2+ elevations elicited by anti-CD3 antibody were diminished in KD mutant T cells and Store-operated calcium entry (SOCE) measured in activated KD splenocytes was reduced
We investigated if Transient Receptor Potential Melastatin 7 (TRPM7) or TRPM6 mRNA levels are changed by phorbol myristate acetate (PMA)/ionomycin treatment, as is the case for numerous T-cell specific genes
The percentage of cells below 8.05 μm was higher in KD, whereas the percentage of cells above 8.05 μm was lower (Supplementary Fig. S5). These results suggest that the percentage of blasting T cells as well as mean extent of enlargement were reduced in KD mice, indicating that TRPM7 kinase plays an important role in T-cell receptor (TCR)-mediated activation process
Summary
Ca2+ elevations elicited by anti-CD3 antibody were diminished in KD mutant T cells and SOCE measured in activated KD splenocytes was reduced These results demonstrate that a functional TRPM7 kinase supports robust SOCE, blastogenesis and proliferation, whereas its inactivation suppresses these cellular events. Despite the high sensitivity of TRPM7 channels to Mg2+, significant basal currents are present in various cell types even before Mg2+ removal[8,9,10]. This observation is surprising, since the cytoplasmic [Mg2+] of ~1 mM11 would be sufficient to inhibit the majority of TRPM7 channels. The kinase domain has been suggested to play a role in cellular Mg2+ homeostasis: mice heterozygous for TRPM7 kinase deletion exhibited hypomagnesemia and reduced channel activity[29]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
