Enhancement of myosin heavy chain class I (MHC I) mRNA expression in C2C12 myocyte by multivalent cations

Our previous study using differentiated C2C12 cells indicated that myosin heavy chain (MHC), interleukin-6 (IL-6) and heat shock protein 70 (HSP70) mRNA expression levels were significantly increased by the application of La3+ to the culture medium. The effects of La3+ on these mRNA levels might be considered as a result of calcineurin activation, because it was known that La3+ stimulates the activity of calcineurin. In the present study, we examined the effects of multivalent cations including La3+, Gd3+, or Ni2+ on expression levels of MHC I, IL-6, and HSP70 mRNA in C2C12 cells. C2C12 cells were induced to differentiate from myotubes by medium exchange to D-MEM containing 2% FCS. The cells were incubated in D-MEM containing 2% FCS with multivalent cations at the beginning of differentiation and removed after 24 hr, and were maintained in differentiation medium for 3 days. Our results are as follows: (1) The MHC I, IL-6, and HSP70 mRNA expression levels were significantly increased by La3+, but were decreased by cyclosporine A with or without La3+. (2) The MHC I mRNA expression level was significantly increased by the application of Gd3+ or Ni2+, although the HSP70 mRNA expression was not affected. (3) The IL-6 mRNA expression level was significantly decreased by the application of Ni2+, but was not affected by the application of Gd3+. These results indicated that La3+ in the culture medium flowed into the cytosol through some kind of ion channels, then upregulates these mRNA levels in calcineurin-dependent manner. The modulating mechanisms of the mRNA levels by Gd3+ or Ni2+ were still unclear. Further experiments need to be done to clarify the effects of multivalent cations on these mRNA expressions in C2C12 cells.