The Ca2+ channel Orai3 drives gemcitabine resistance in pancreatic cancer through NFATc1-dependent SLIT3 expression.

Pancreatic Cancer (PC) is one of the most aggressive cancers and is associated with poor prognosis. One of the routinely used chemotherapeutic drugs for the treatment of advanced PC is gemcitabine, which offers survival benefits to patients. However, acquired gemcitabine-resistance leads to recurrence, metastasis, and the long-term prognosis remains poor. Although there is substantial clinical evidence of gemcitabine resistance, the cellular and molecular mechanisms that drive this resistance remain largely unappreciated. Here, we reveal that Orai3, a Ca2+-selective channel, is a crucial inducer of gemcitabine resistance. We demonstrate that Orai3 is overexpressed and hyper-functional in gemcitabine-resistant PC cells. Orai3 silencing in gemcitabine-resistant cells enhances chemo-sensitivity, inhibits migration, stalls invasion, and moderates stemness characteristics. Notably, studies in the zebrafish model corroborate Orai3's significance in gemcitabine-resistance in vivo. Mechanistically, our unbiased RNA-seq analysis, coupled with robust functional studies, reveals that a secretory repulsive axon guidance molecule Slit guidance ligand 3 (SLIT3) acts downstream of Orai3 to induce gemcitabine resistance. Finally, we report that the Nuclear Factor of Activated T cells 1 (NFATc1) transcription factor bridges Orai3 to SLIT3 transcription. Taken together, this study reveals Orai3 as a promising target to combat gemcitabine-resistance and uncovers a unique Orai3-NFATc1-SLIT3 signaling module that drives chemoresistance.