ZnT1 induces a crosstalk between T-type and L-type calcium channels through interactions with Raf-1 kinase and the calcium channel β2 subunit.

Abstract

ZnT1 is a major zinc transporter that regulates cellular zinc homeostasis. We have previously shown that ZnT1 has additional functions that are independent of its activity as a Zn2+ extruder. These include inhibition of the L-type calcium channel (LTCC) through interaction with the auxiliary β-subunit of the LTCC and activation of the Raf-ERK signaling leading to augmented activity of the T-type calcium channel (TTCC). Our findings indicate that ZnT1 increases TTCC activity by enhancing the trafficking of the channel to the plasma membrane. LTCC and TTCC are co-expressed in many tissues and have different functions in a variety of tissues. In the current work, we investigated the effect of the voltage-gated calcium channel (VGCC) β-subunit and ZnT1 on the crosstalk between LTCC and TTCC and their functions. Our results indicate that the β-subunit inhibits the ZnT1-induced augmentation of TTCC function. This inhibition correlates with the VGCC β-subunit-dependent reduction in ZnT1-induced activation of Ras-ERK signaling. The effect of ZnT1 is specific, as the presence of the β-subunit did not change the effect of endothelin-1 (ET-1) on TTCC surface expression. These findings document a novel regulatory function of ZnT1 serving as a mediator in the crosstalk between TTCC and LTCC. Overall, we demonstrate that ZnT1 binds and regulates the activity of the β-subunit of VGCC and Raf-1 kinase and modulates surface expression of the LTCC and TTCC catalytic subunits, consequently modulating the activity of these channels.