L-type voltage-gated Ca2+ channels control T cell killing via non-canonical Hedgehog signaling

Cytotoxic CD8+ T lymphocytes (CTLs) efficiently eliminate infected and cancerous cells throughout the body. Hedgehog signaling is critical for CTL-mediated killing. Remarkably the pathway cannot be induced canonically by extracellular Hedgehog ligands but instead is activated by the T cell receptor (TCR). How the Hedgehog pathway is mechanistically activated downstream of the TCR is unknown. Here we show that L-type voltage gated Ca2+ (Cav1) channels at the plasma membrane downstream of the TCR control an extracellular Ca2+ influx leading to induction of the Hedgehog transcription factor Gli1 which is essential for efficient CTL killing in vitro and in vivo. This novel non-canonical Hedgehog pathway is independent of canonical signaling and represents a primary mechanism of Gli1 induction in naive CD8+ T cells, while CTLs can also activate Gli1 via MAPK. We show that Cav1 channel-controlled Gli1 induction is functionally required for CTL killing in mice and humans and other cytotoxic lymphocytes. Importantly, we demonstrate that killing capacity can be amplified using a small molecule Cav1 channel agonist or by overexpression of a gain-of-function Cav1 subunit. Our findings indicate that Gli inhibitors, currently in clinical trials as anti-cancer therapeutics, likely inhibit the cytotoxic anti-tumor response. On the other hand, our work opens up the possibility to enhance CTL performance in the clinic by selectively increasing Ca2+ flux via Cav1 channels, for example in the context of CAR T cell therapy.