Calcium-sensing receptor gene transcription is up-regulated by the proinflammatory cytokine, interleukin-1β -: Role of the NF-κB pathway and κB elements

The calcium- sensing receptor ( CASR) in parathyroid, thyroid, and kidney is essential for calcium homeostasis. Hypocalcemia is common in critically ill patients having increased circulating proinflammatory cytokines, although the causes are unknown. We hypothesized that the cytokines increase CASR expression and reduce the set point for parathyroid hormone suppression by extracellular calcium, leading to hypocalcemia and hypoparathyroidism. Here, we show in vivo in the rat that parathyroid, thyroid, and kidney CASR mRNA and protein increased after injection of interleukin- 1 beta. This was associated with decreased circulating parathyroid hormone, calcium, and 1,25- dihydroxyvitamin D levels. Interleukin- 1 beta stimulated endogenous CASR gene transcripts and transfected promoter reporter activity in human thyroid C- cells ( TT cells) and kidney proximal tubule ( HKC) cells. Cotransfection of NF- kappa B proteins enhanced activity of the reporter constructs, whereas cotransfection with inhibitor- kappa B or application of an NF- kappa B nuclear localization sequence peptide abrogated responsiveness to cytokine or NF- kappa B proteins. Mutagenesis of some, but not all, of the potential kappa B elements in the 5 ' part of the CASR gene led to loss of responsiveness to cytokine. These elements conferred cytokine responsiveness to a heterologous promoter, and in electrophoretic mobility shift assays, NF- kappa B complexes formed on the same three kappa B elements. In summary, the CASR gene has several functional kappa B elements that mediate its upregulation by proinflammatory cytokines and probably contribute to altered extracellular calcium homeostasis in the critically ill.