Campari2 genomic interrogation of homeostatic calcium activity identifies TIM1 as a negative regulator of T cell function.

Calcium signals regulate crucial cellular functions yet many genes coding for Cahandling proteins remain unknown as their identification relies on low-throughput single-cell approaches. Here we describe a method to measure Ca activity using CaMPARI2, flow cytometry and pooled genome interrogation. CAMPARI2 screen (CaMP-Screen) identified enhancers and inhibitors of homeostatic Ca activity, highlighting a predominant role for store-operated Ca entry (SOCE) and lipid signalling pathways. Genes reducing basal Ca activity were linked to Prader Willy syndrome, T cell dysfunction, and deafness. Silencing of HAVCR1 gene, coding for T cell transmembrane immunoglobulin and mucin (TIM1), enhanced Ca signals in T cells and promoted signaling under resting but not after TCR engagement. Our findings establish CaMP-Screen as an efficient detector of low-amplitude Ca signals and identify new genes associated to pathologies that regulate Ca homeostasis, reporting TIM1 as a negative regulator of Ca signals driving T cell function.