Activity of Potassium Channels in CD8+ T Lymphocytes: Diagnostic and Prognostic Biomarker in Ovarian Cancer?

CD8+ T cells play a role in the suppression of tumor growth and immunotherapy. Ion channels control the Ca2+-dependent function of CD8+ lymphocytes such as cytokine/granzyme production and tumor killing. Kv1.3 and KCa3.1 K+ channels stabilize the negative membrane potential of T cells to maintain Ca2+ influx through CRAC channels. We assessed the expression of Kv1.3, KCa3.1 and CRAC in CD8+ cells from ovarian cancer (OC) patients (n = 7). We found that the expression level of Kv1.3 was higher in patients with malignant tumors than in control or benign tumor groups while the KCa3.1 activity was lower in the malignant tumor group as compared to the others. We demonstrated that the Ca2+ response in malignant tumor patients is higher compared to control groups. We propose that altered Kv1.3 and KCa3.1 expression in CD8+ cells in OC could be a reporter and may serve as a biomarker in diagnostics and that increased Ca2+ response through CRAC may contribute to the impaired CD8+ function.

Molecular background of Orai1 accumulation in the immunological synapse

CRAC channels have a vital role in the activation of T lymphocytes, through their calcium influx. CRAC is composed of the ER-membrane resident STIM1 (stromal interaction molecule 1) and the plasma membrane Orai1 pore-forming subunit. Both are accumulated at the interface of the immunological synapse (IS) between a T cell and an antigen-presenting cell (APC). CRAC channelopathies due to mutations in either Orai1 or STIM1 are characterized by severe combined immunodeficiency (SCID)-like disease, autoimmunity, muscular hypotonia, and ectodermal dysplasia. The down-regulation of actin-binding protein expression (e.g. HS1), which may be responsible for the immobilization of ion channels, hampers Ca2+-signaling and IS formation of T lymphocytes. We hypothesized that actin-binding proteins modulate the trafficking of the CRAC channels to the IS, which is crucial for the Ca2+-signaling. By means of GST-affinity assay we could show that HS1, which is an actin-regulatory adaptor protein, binds to the N-terminus of the Orai1. N-terminal truncated Orai1 channels (ΔN1: 1–74, ΔN2: 1–88) were created and expressed in Jurkat cells. Then Orai1 channel expressing Jurkat cells were conjugated to CD3/CD28 beads as an APC and Orai1 polarization was determined: the Orai1-ΔN1 mutant similar to the wild-type Orai1 redistributed to the IS but the Orai1-ΔN2 did not. Furthermore, the HS1 protein did not show IS-accumulation in cells expressing the Orai1-ΔN2 subunits unlike for those transfected with the Orai1-ΔN1 or the wild-type constructs. Overall, these data indicate that Orai1-HS1 interaction could contribute to the anchoring of the Orai1 in the IS and can affect the Ca2+-signaling upon T cell activation.