Sphingolipid metabolites selectively elicit increases in nuclear calcium concentration in cell suspension cultures and in isolated nuclei of tobacco

Sphingolipids are known to interfere with calcium-based signalling pathways. Here we report that these compounds modulate nuclear calcium signalling in tobacco BY-2 cells. Nuclear protein kinase activity phosphorylated endogenous sphingoid long-chain bases (LCBs), suggesting that LCBs are actively metabolized in the nucleus of tobacco BY-2 cells. The Δ4-unsaturated LCB d-erythro-sphingosine and the saturated LCB d-ribo-phytosphingosine elicited increases in free calcium in the nucleus in a dose-dependent and structure-related manner. However, neither sphingosine-1-phosphate nor C2-ceramide was able to stimulate nuclear calcium changes. N-,N-Dimethyl-d-erythro-sphingosine, a structural analogue of d-erythro-sphingosine, was the most efficient LCB so far tested in eliciting nuclear calcium changes both in intact tobacco BY-2 cells and in isolated nuclei. TRP channel inhibitors prevent the effect of DMS, suggesting that LCBs may activate TRP-like channels located on the inner nuclear membrane Collectively, the obtained data show that nuclei respond to LCBs on their own independently of the cytosolic compartment.