The Master Switch of T Cell Activation: A Novel Immune Regulatory Mechanism of ANO9

I. Molecular Biological Characteristics of the ANO9 Target

ANO9 (TMEM16J) is a transmembrane protein with a typical topology of the Anoctamin family, containing 8 transmembrane domains. It is mainly localized to the endoplasmic reticulum (ER) and ER-Golgi intermediate compartment (ERGIC), which is closely related to its functions in membrane protein transport and quality control. 

 (1) Ion channel and phospholipid scramblase activity: Some members of the Anoctamin family exhibit Ca²⁺-activated chloride channel activity. Although the specific ion permeability of ANO9 remains under intensive investigation, several studies suggest its potential involvement in regulating membrane potential or intracellular ionic environment. Furthermore, as a member of the family with phospholipid scramblase activity, ANO9 may modulate cell signaling and membrane dynamics by affecting the asymmetric distribution of phospholipids. 

 (2) Regulator of vesicular trafficking: Accumulating evidence indicates that ANO9 acts as a “chaperone” or regulator in the secretory pathway of proteins. It may assist the transport of certain membrane proteins (e.g., ion channels and receptors) from the ER to the plasma membrane, affecting their expression abundance on the cell surface.

II. Core Research Content and Findings

1. ANO9 is a Key Regulator of T Cell Activation

The study found that depletion of ANO9 (by knockout or knockdown) results in significantly diminished Ca²⁺ signaling following T cell receptor (TCR) activation, reduced cell proliferation, and decreased interleukin-2 (IL-2) release in both human Jurkat T cell line and primary human T cells. Specifically, ANO9 knockout (KO) Jurkat cells display markedly reduced elevation of intracellular Ca²⁺ concentration upon CD3/CD28 stimulation compared with wild-type (WT) cells. This Ca²⁺ signaling defect mainly arises from impaired store-operated Ca²⁺ entry (SOCE). Similarly, ANO9 knockdown in primary human T cells inhibits SOCE enhancement and IL-2 mRNA expression induced by CD3/CD28 stimulation. Furthermore, flunisolide, a potential ANO9 inhibitor, effectively suppresses the activation of WT Jurkat cells, further supporting the functional importance of ANO9. 

(Impaired Ca²⁺ Signaling in ANO9-KO Human Jurkat T Cells. )  

(Validation in Primary Human T Cells.)              

2. ANO9 Regulates Ca²⁺ Signaling by Promoting PMCA Membrane Translocation 

The study proposes the mechanism of ANO9: it functions by promoting the translocation of PMCA to the plasma membrane (especially at the immunological synapse) during cell activation. PMCA is responsible for pumping intracellular Ca²⁺ out of the cell, maintaining a low-Ca²⁺ microdomain environment, thereby avoiding Ca²⁺-dependent negative feedback inhibition of Ca²⁺ release-activated Ca²⁺ channels (e.g., Orai1) and ensuring sustained and efficient Ca²⁺ entry. Immunofluorescence experiments confirm that PMCA signals on the membrane of WT Jurkat cells are significantly enhanced and exhibit a granular distribution after CD3 stimulation, whereas this enhancement is greatly diminished in ANO9 KO cells. Furthermore, vitamin D3 (Vit-D3), which exerts immunomodulatory functions, upregulates PMCA membrane expression in activated T cells, but this effect is abolished in ANO9 KO cells, indicating that ANO9 is a potential mediator for Vit-D3 to exert immunomodulatory effects.     

(ANO9 Regulates Ca²⁺ Signaling by Promoting PMCA Membrane Translocation. )            

3. ANO9 Variant T604A/T595A Induces Lymphocyte Hyperactivation 

The study focuses on a human ANO9 variant T604A (corresponding to T595A in mice) associated with chronic kidney disease. To investigate its function, the authors generated T595A knock-in mice. In contrast to the reduced activity caused by ANO9 depletion, the T595A variant exhibits a gain-of-function effect. Lymphocytes isolated from these mice show: 

 (1) Both mouse wild-type (wt-Ano9) and T595A-Ano9 lymphocytes display upregulated Ano9 expression during CD3/28 activation. 

(2) Lymphocytes expressing T595A-ANO9 exhibit enhanced immune activity.  

(3) Lymphocytes expressing T595A-ANO9 display larger whole-cell ionic currents during CD3/28 activation.   

(4) Enhanced Ca²⁺ signaling: increased amplitude of intracellular Ca²⁺ elevation, augmented basal Ca²⁺ influx and SOCE following CD3/CD28 stimulation.    

These results indicate that the T604A/T595A variant may cause lymphocyte hyperactivation, providing mechanistic insights into how this variant triggers chronic kidney disease by promoting inflammation. 

 4. Differential Expression of ANO9 in Human and Mouse Lymphocytes 

The study notes distinct expression patterns of ANO9 in human and mouse lymphocytes. Under non-activated conditions, Ano9 expression in mouse lymphocytes is much lower than in human lymphocytes. However, following CD3/CD28 activation, Ano9 expression is significantly upregulated in mouse lymphocytes, whereas ANO9 expression is suppressed during activation in human lymphocytes.

III. Summary

Using three complementary strategies—gene knockout, siRNA knockdown, and point mutation knock-in—this study systematically demonstrates that ANO9 is a critical regulator of Ca²⁺ signaling and immune activation in T lymphocytes. Its depletion leads to immunodeficiency, whereas the disease-associated mutation T604A/T595A results in lymphocyte hyperactivation and enhanced inflammatory responses, which may explain the pathogenesis of chronic kidney disease and inflammatory disorders in patients carrying this mutation.

Antibodies Used in This Study:

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