TSH/cAMP up-regulate sarco/endoplasmic reticulum Ca2+-ATPases expression and activity in PC Cl3 thyroid cells

Objective: We recently reported that the sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) 2b is the SERCA form preferentially expressed in rat thyroid. Moreover, SERCA2b expression dramatically decreases in virally transformed, highly tumorigenic, PC Cl3 thyroid cells. These results suggest that, in the thyroid, SERCA2b, in addition to its housekeeping role, is linked to differentiation and is a regulated gene. We therefore sought to study the effect of TSH, the main regulator of thyroid function, on SERCA2b expression and activity. Methods: PC Cl3 cells were hormone starved in low-serum medium and stimulated for long (48 h) or short (1, 2 and 4 h) times. SERCA2b expression and activity were evaluated by Northern and Western blots, Ca²⁺-ATPase activity and Ca²⁺ store content. Results: In PC Cl3 cells, SERCA2b mRNA and protein were induced twofold by a 48-h long treatment with TSH. Long-term elevation (48 h) of intracellular cAMP levels, by forskolin or 8-Br-cAMP, had similar effects on SERCA2b mRNA and protein. We also measured Ca²⁺-ATPase activity and Ca²⁺ store content. Both long (48 h) and short (0.5-1 h) treatments with TSH, forskolin or 8-Br-cAMP induced a marked increase of SERCA2b activity. This effect was completely abolished by H89, a specific inhibitor of cAMP-dependent protein kinase A (PKA). TSH and 8-Br-cAMP increased Ca²⁺ store content after both long (48 h) and short (1-2 h) treatments. Conclusions: These data suggested that TSH/cAMP acts as an important regulator of both SERCA2b expression and activity in the thyroid system, through PKA activation.