Evaluating the role of dibutyl-cAMP and Ca++ as an MT inducer in a clonal rat hepatoma cell

Abstract

Metallothioneins (MT) is a low molecular weight, cysteine-rich, metal-binding protein that can be induced when cells and tissues are exposed to metal such as Cd, Zn, Cu and Hg. MT could also be induced by non-metallic stimuli including physiological, chemical and pathological stresses. It has been suggested that signalling molecules such as cAMP or Ca ++ might also induce MT. In the present study, the mode of induction of MT in the RH-35 cells was investigated with reference to the integrity of the cells. The degree of MT induction was measured by the Cd-saturation assay in which total Cd bound to the heat-stable MT was determined by the graphite furnace atomic absorption spectrometry. It was demonstrated that Zn and Cd could markedly increase cellular MT content. Alpha-amanitin, which blocks DNA transcription, can significantly decrease the Cd induced MT induction. MT induction was also lowered by cycloheximide, which blocks protein translation. However, dibutyl-cAMP, Ca ++ and Ca ++ in the presence of ionomycin were unable to induce cellular MT. Using this model, the results supported that notion that MT induction might not be mediated by cAMP or Ca ++ in this cell line.