Optimal immune responses require adequate ionic supply and carefully regulated ion-homeostasis. The adverse effects of low-Mg2+ conditions on immunity are well documented, but mechanistic insights into this Mg2+-sensitivity are lacking. The recently discovered protein TRPM7 is the unique fusion of an active Ser/Thr kinase with an ion channel, and a master regulator of Mg2+-homeostasis. TRPM7 has been shown to interact with several phospholipase C (PLC) isozymes. PLC proteins are at the heart of crucial signaling pathways required for the development and activation of virtually every immune cell type, including B-lymphocytes, which are the cellular architects of humoral immune responses. PLCg2 is central to B-cell receptor (BCR) signaling, and mediates B- cell maturation as well as activation. We propose that TRPM7-kinase modulates BCR- signaling in accordance to the availability of Mg2+ through Ser/Thr phosphorylation of PLCg2. The regulation of PLCg2 by Tyr-phosphorylation has been amply characterized, but its modulation by Ser/Thr phosphorylation is only postulated, although highly probable, since the vast majority of cellular phosphorylation events involve Ser/Thr residues. We have gathered preliminary experimental evidence in cell lines supporting our main hypothesis that the C2-domain of PLCg2 is a substrate of TRPM7-kinase, resulting in the Mg2+-sensitive modulation of BCR-elicited Ca2+-responses. This proposal aims at further exploring the effect of this novel phosphorylation event on PLCg2's localization, Tyr-phosphorylation and enzymatic activity, as well as to investigate its physiological relevance in vivo using a complementation approach in an existing mouse model of PLCg2 deficiency.

Public Health Relevance

Alterations in ion homeostasis have severe effects on human health, impairing the effectiveness and appropriateness of immune responses, and causing or exacerbating grave diseases such as cancer or diabetes. The planned studies will contribute to expanding our knowledge about molecular mechanisms allowing for the adjustment of immune responses to the availability of the essential and most abundant intracellular divalent cation Mg2+. Understanding these regulatory processes represent potential opportunities to develop novel immunomodulatory strategies for therapeutic intervention. Given its focus on B-lymphocytes, this proposal is relevant to conditions such as auto-immune diseases, or various forms of immunodeficiencies.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Exploratory/Developmental Grants (R21)
Project #
1R21AI088421-01
Application #
7875500
Study Section
Cellular and Molecular Immunology - B Study Section (CMIB)
Program Officer
Ferguson, Stacy E
Project Start
2010-06-01
Project End
2012-05-31
Budget Start
2010-06-01
Budget End
2011-05-31
Support Year
1
Fiscal Year
2010
Total Cost
$229,563
Indirect Cost
Name
University of Colorado Denver
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
041096314
City
Aurora
State
CO
Country
United States
Zip Code
80045
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Brandao, Katherine; Deason-Towne, Francina; Zhao, Xiaoyun et al. (2014) TRPM6 kinase activity regulates TRPM7 trafficking and inhibits cellular growth under hypomagnesic conditions. Cell Mol Life Sci 71:4853-67
Brandao, Katherine; Deason-Towne, Francina; Perraud, Anne-Laure et al. (2013) The role of Mg2+ in immune cells. Immunol Res 55:261-9
Yogi, Alvaro; Callera, Glaucia E; O'Connor, Sarah et al. (2013) Aldosterone signaling through transient receptor potential melastatin 7 cation channel (TRPM7) and its ?-kinase domain. Cell Signal 25:2163-75
Deason-Towne, Francina; Perraud, Anne-Laure; Schmitz, Carsten (2012) Identification of Ser/Thr phosphorylation sites in the C2-domain of phospholipase C ?2 (PLC?2) using TRPM7-kinase. Cell Signal 24:2070-5