Loureirin B Exerts its Immunosuppressive Effects by Inhibiting STIM1/Orai1 and K(V)1.3 Channels

Loureirin B (LrB) is a constituent extracted from traditional Chinese medicine Resina Draconis. It has broad biological functions and an impressive immunosuppressive effect that has been supported by numerous studies. However, the molecular mechanisms underlying Loureirin B-induced immune suppression are not fully understood. We previously reported that Loureirin B inhibited K(V)1.3 channel, calcium ion (Ca(2+)) influx, and interleukin-2 (IL-2) secretion in Jurkat T cells. In this study, we applied CRISPR/Cas9 to edit K(V)1.3 coding gene KCNA3 and successfully generated a K(V)1.3 knockout (KO) cell model to determine whether K(V)1.3 KO was sufficient to block the Loureirin B-induced immunosuppressive effect. Surprisingly, we showed that Loureirin B could still inhibit Ca(2+) influx and IL-2 secretion in the Jurkat T cells in the absence of K(V)1.3 although KO K(V)1.3 reduced about 50% of Ca(2+) influx and 90% IL-2 secretion compared with that in the wild type cells. Further experiments showed that Loureirin B directly inhibited STIM1/Orai1 channel in a dose-dependent manner. Our results suggest that Loureirin B inhibits Ca(2+) influx and IL-2 secretion in Jurkat T cells by inhibiting both K(V)1.3 and STIM1/Orai1 channels. These studies also revealed an additional molecular target for Loureirin B-induced immunosuppressive effect, which makes it a promising leading compound for treating autoimmune diseases.