Thyroid hormone-induced stimulation of the sarcoplasmic reticulum Ca2+ ATPase gene is inhibited by LIF and IL-6

We investigated the effects of the leukemia inhibitory factor (LIF) and int erleukin-6 (IL-6) on 3,3', 5-triiodo-L-thyronine, or thyroid hormone (T-3)- stimulated sarcoplasmic reticulum Ca2+ ATPase (SERCA2) gene expression on c ultured neonatal rat cardiac myocytes. A reduction of Ta induced increases in SERCA2 mRNA levels after co-treatment with LIF or IL-6. To investigate f or the molecular mechanism(s) responsible for the blunted gene expression, a 3.2-kb SERCA2 promoter construct containing a reporter gene was transfect ed into cardiac myocytes. T-3 treatment stimulated transcriptional activity twofold, whereas co-treatment with T-3 and either of the cytokines caused an inhibition of T-3-induced SERCA2 transcriptional activity. A T-3-respons ive 0.6-kb SERCA2 construct also showed a similar inhibition by cytokines. Cytokine inhibition of SERCA2 transcriptional activity was also evident whe n a 0.6-kb SERCA2 mutant, T-3-unresponsive promoter construct was used. Tre atment with T-3 and cytokines showed a significant decrease in transcriptio n when a reporter construct was used that was comprised of direct repeats o f SERCA2 thyroid response element I. These data provide evidence for cytoki ne-mediated inhibitory effects on the SERCA2 promoter that may be mediated by interfering with T-3 action.