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ARS Home » Pacific West Area » Davis, California » Western Human Nutrition Research Center » Obesity and Metabolism Research » Research » Publications at this Location » Publication #333027
Title: ZNT7 binds to CD40 and influences CD154-triggered p38 MAPK activity in B lymphocytes-a possible regulatory mechanism for zinc in immune function

Author
item TEPAAMORNDECH, SURAPUN - University Of California
item Oort, Pieter
item Kirschke, Catherine
item YIMENG, CAI - University Of California
item Huang, Liping

Submitted to: FEBS Open Bio
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2017
Publication Date: 3/27/2017
Citation: Tepaamorndech, S., Oort, P.J., Kirschke, C.P., Yimeng, C., Huang, L. 2017. ZNT7 binds to CD40 and influences CD154-triggered p38 MAPK activity in B lymphocytes-a possible regulatory mechanism for zinc in immune function. FEBS Open Bio. 7(5):675–690. doi: 10.1002/2211-5463.12211.

Interpretive Summary: Zinc deficiency impairs the immune system leading to frequent infections in humans. Although it is known that zinc plays critical roles in maintaining healthy immune function, the underlying molecular targets are largely unknown. In this study, we showed that zinc is important for the CD154-CD40-mediated activation of downstream signaling transduction in human B lymphocytes. CD40 is a receptor protein (a protein that takes signal from stimuli from outside of the cell) localized on the cell surface of many immune cells. When activated, T helper lymphocytes (Th, one kind of regulatory immune cell) present antigens (a piece of digested foreign proteins, such as bacterial proteins) to B lymphocytes (a kind of immune cell that secretes antibodies), it produces a protein called CD154 on the cell surface. CD154 can bind to CD40 that brings T and B cells together. This binding triggers many signaling cascades in B cells leading to B cell growth and antibody secretion. We demonstrated that zinc deficiency in B cells impaired this CD154-CD40 binding which result in impaired p38 MAPK activation (an enzyme that can activate other enzymes’ activities in a given cell). We also demonstrated that zinc supplementation of B lymphocytes had limited effect on this p38 MAPK signaling. Most importantly, we demonstrated that ZNT7 could physically interact with CD40, and ZNT7 knockdown (reduced production of the protein in the cell) had a negative effect on the amount of CD40 on the B cell surface. As a result, ZNT7 knockdown resulted in down-regulation of CD154-CD40-mediated p38 MAPK signaling transduction whereas over-expression of ZNT7 up-regulated p38 MAPK activity in B lymphocytes. Moreover, we found that ZNT7 knockdown in B lymphocytes constitutively up- and down-regulated IKK and AKT activities (enzymes that also can stimulate other protein activities in a given cell), respectively, without bringing T cells and B cells together, which may lead to B cell tumorigenesis. We conclude that prevention of zinc deficiency is a key to maintain an optimal function of the immune system and CD40 is the molecular target for ZNT7 in regulation of immune function.

Technical Abstract: Zinc deficiency impairs immune system leading to frequent infections. Although it is known that zinc plays critical roles in maintaining healthy immune function, the underlying molecular targets are largely unknown. In this study, we showed that zinc is important for the CD154-CD40-mediated activation of downstream signaling pathways in human B lymphocytes. CD40 is a receptor protein localized on the cell surface of many immune cells. When activated T helper lymphocytes (Th) present antigens to B lymphocytes, they express a membrane-bound ligand protein, CD154, whereby Th cells binds to B lymphocytes via CD154-CD40 interaction. This interaction triggers many intracellular signaling cascades leading to B cell activation. We demonstrated that cellular zinc deficiency impaired the CD154-CD40-mediated p38 MAPK phosphorylation. We also demonstrated that zinc supplemental treatment of B lymphocytes had limited effect on this CD40-mediated p38 MAPK signaling. Most importantly, we demonstrated that ZNT7 could physically interact with CD40, and ZNT7 knockdown had a negative effect on the cell surface expression of CD40. As a result, ZNT7 knockdown resulted in down-regulation of CD154-CD40-mediated p38 MAPK signaling transduction whereas over-expression of ZNT7 up-regulated p38 MAPK activity in B lymphocytes. Moreover, we found that ZNT7 knockdown in B lymphocytes constitutively up- and down-regulated IKK and AKT phosphorylation, respectively, in a CD154-CD40-independent manner which may lead to B cell tumorigenesis. We conclude that prevention of zinc deficiency is a key to maintain an optimal function of the immune system and CD40 is the molecular target for ZNT7 in regulation of immune function.