Increased synthesis and degradation of DNA topoisomerase I during the initial phase of human T lymphocyte proliferation

Ching Long Hwongt, Ching Yi Chen, Huey Fang Shang, Jaulang Hwang

Research output: Contribution to journalArticle

28 Citations (Scopus)

Abstract

The regulation of DNA topoisomerase I was studied in human T lymphocytes following phytohemagglutinin (PHA) stimulation. As T lymphocytes began to enter the S phase 24 h after stimulation, there was a rapid increase in DNA topoisomerase I mRNA. The level of DNA topoisomerase I mRNA increased continuously over the next 18 h and peaked (>50-fold increase) 42 h after stimulation with PHA. A concomitant increase in DNA topoisomerase I protein was also observed. However, the maximal increase in DNA topoisomerase I protein was only 6-fold. To explain the quantitative difference between the mRNA and protein levels, we investigated the change in the rates of DNA topoisomerase I protein synthesis versus degradation in human T lymphocytes following PHA stimulation. The increase in the mRNA parallels the increase in protein synthesis. However, the half-life of the enzyme protein was reduced to 9 h in proliferating T lymphocytes compared to a half-life of 36 h in resting lymphocytes. These results indicate that, in addition to the growth-regulated increase in the expression of DNA topoisomerase I, there was also a concomitant increase in the degradation of DNA topoisomerase I protein.

Original languageEnglish
Pages (from-to)18982-18986
Number of pages5
JournalJournal of Biological Chemistry
Volume268
Issue number25
Publication statusPublished - Sep 5 1993
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry

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