Induction of metallothionein mRNA and protein in murine astrocyte cultures

Astrocytes are known to express metallothionein (MT) and were studied in culture to determine whether MT could be directly induced and which isoforms are induced. Primary astrocyte cultures were established from neonatal CF-1 mice. Both concentration-response and time-course analyses for MT induction at the protein level were determined. At the mRNA level, induction of MT-I, -II, and -III was examined 6 hr following the addition of the inducing agents. Dexamethasone (Dex), cadmium (Cd), mercury (Hg), or zinc (Zn) increased (three- to fourfold) MT protein in the astrocytes, whereas methyl mercury, lead, and interleukin-1 and -6 were ineffective. Cadmium was the most potent inducer, but was not more effective than Hg or Zn in inducing MT protein. All effective inducers increased MT protein by 24 hr. After 48 hr, Hg caused cell death, but all other effective inducers increased the MT protein examined over the 5 days. Cadmium induction of MT protein reached a peak at 96 hr, whereas the other effective inducers stimulated maximal MT protein at 24-48 hr. The effects of Dex, Cd, and Zn, on MT-I, -II, and -III mRNAs were also examined. Cadmium, Zn, and Dex stimulated increases in both MT-I and MT-II mRNA, with Dex producing the greatest effect (2.0- and 3.5-fold for MT-I and -II mRNA, respectively). Metallothionein-III mRNA was relatively unresponsive to induction. Therefore, Cd, Zn, and Dex induced MT-I and -II mRNA but not MT-III mRNA in astrocytes. These results demonstrate that MT-I and -II are directly induced in mouse astrocyte primary cultures.