Human metallothionein isoform gene expression in cisplatin-sensitive and resistant cells.

Abstract

Overexpression of metallothioneins (MTs) has been observed in some cis-diamminedichloroplatinum (CDDP)-resistant cells. We have developed oligonucleotide probes for each of the six non-neuronal human MT (hMT) isoforms and used them to assay hMT isoform expression in three pairs of CDDP-resistant and -sensitive human carcinoma cell lines, i.e., SCC25/CP versus SCC25 cells, H69/CP versus H69 cells, and SW2/CP versus SW2 cells. We found a 9-fold increase in basal hMT-IIa mRNA levels and a 5-fold increase in hMT-le mRNA levels in SCC25/CP cells, compared with SCC25 cells. Nuclear run-on studies also revealed a 3-fold increase in hMT-IIa transcription rate. Basal hMT-IIa steady state mRNA levels were 2-3.6-fold greater in H69/CP and SW2/CP cells, compared with their parental cells. No significant basal expression of hMT-Ia, -Ib, -If, or Ig was detected in any cells, suggesting that overexpression of these isoforms was not commonly associated with the CDDP-resistant phenotype. Levels of constitutively expressed hMT isoforms, as well as hMT-If, could be elevated by treatment of all cells with 100 microM zinc. The universal overexpression of hMT-IIa suggests a role of this particular isoform in CDDP resistance. Using our isoform-specific hMT-IIa probe and the demethylating agent 5'-azacytidine (AZC), we found that AZC pretreatment increased basal hMT-IIa mRNA levels in SCC25 but not SCC25/CP cells, suggesting that DNA hypomethylation was responsible for higher basal hMT-IIa mRNA levels in SCC25/CP cells. AZC had little or no effect on hMT-If or -Ig expression. Limited restriction analysis by methylation-sensitive enzymes, however, revealed no obvious differences in the methylation status of the hMT-IIa promoter in either SCC25 or SCC25/CP cells.

• Authors: Y Y Yang, E S Woo, C E Reese, R R Bahnson, N Saijo, J S Lazo
• Journal: Molecular pharmacology (Mol Pharmacol) Vol. 45 Issue 3 Pg. 453-60 (Mar 1994) ISSN: 0026-895X [Print] United States
• PMID: 7511778 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Metals
• RNA, Messenger
• Metallothionein
• Azacitidine
• Cisplatin

Topics

• Azacitidine (pharmacology)
• Base Sequence
• Cisplatin (pharmacology)
• Drug Resistance
• Gene Expression (drug effects)
• Humans
• Metallothionein (biosynthesis, genetics)
• Metals (pharmacology)
• Molecular Sequence Data
• RNA, Messenger (metabolism)
• Restriction Mapping
• Transcription, Genetic
• Tumor Cells, Cultured