Intracellular Ca2+ is not essential for SHH signaling but is promoted by Shh ligand in embryonic fibroblasts.

BACKGROUND

Sonic Hedgehog (SHH) signaling pathway controls cell proliferation, differentiation, and organ formation. The changes in Ca2+ and their regulatory role in the context of activated SHH signaling have not been fully examined.

RESULTS

In this study, we induced activation of the SHH signaling pathway using activators, including Full-length Shh protein (Shh) and N-terminal Shh (ShhN) ligands or a Smoothened agonist (SAG), while concurrently manipulating calcium level by either increasing extracellular Ca2+ concentration or employing BAPTA to chelate intracellular Ca2+. We found that the activation of SHH target genes by the three activators was not affected by low intracellular Ca2+ but inhibited by excess Ca2+. Although both Shh and SAG activate Ca2+ influx via the store-operated calcium entry (SOCE), their effects differ in the presence of BAPTA: Shh directly increases intracellular Ca2+ concentration, whereas the effect of SAG is enhanced by high extracellular Ca2+.

CONCLUSIONS

Excessive extracellular Ca2+ impairs SHH signal transduction, whereas intracellular Ca2+ levels have a negligible effect. At normal physiological extracellular Ca2+ concentrations, the depletion of intracellular Ca2+ does not affect SHH signal transduction.