Pleiotropic roles of Ca(+2)/calmodulin-dependent pathways in regulating cadmium-induced toxicity in human osteoblast-like cell lines.

The heavy metal cadmium is a widespread environmental contaminant that has gained public attention due to the global increase in cadmium-containing electronic waste. Human exposure to cadmium is linked to the pathogenesis of osteoporosis. We previously reported cadmium induces apoptosis and decreases alkaline phosphatase mRNA expression via extracellular signal-regulated protein kinase (ERK) activation in Saos-2 bone-forming osteoblasts. This study examines the mechanisms of cadmium-induced osteotoxicity by investigating roles of Ca(+2)/calmodulin-dependent protein kinase (CAMK) pathways. Saos-2 or MG-63 cells were treated for 24 or 48h with 5μM CdCl2 alone or in combination with calmodulin-dependent phosphodiesterase (PDE) inhibitor CGS-9343β; calmodulin-dependent kinase kinase (CAMKK) inhibitor STO-609; or calmodulin-dependent kinase II (CAMKII) inhibitor KN-93. CGS-9343β protected against cadmium-induced toxicity and attenuated ERK activation; STO-609 enhanced toxicity and exacerbated ERK activation, whereas KN-93 had no detectable effect on cadmium-induced toxicity. Furthermore, CGS-9343β co-treatment attenuated cadmium-induced apoptosis; but CGS-9343β did not recover cadmium-induced decrease in ALP activity. The major findings suggest the calmodulin-dependent PDE pathway facilitates cadmium-induced ERK activation leading to apoptosis, whereas the CAMKK pathway plays a protective role against cadmium-induced osteotoxicity via ERK signaling. This research distinguishes itself by identifying pleiotropic roles for CAMK pathways in mediating cadmium's toxicity in osteoblasts.