Deregulation of DNA polymerase β by sense and antisense RNA expression in mouse 3T3 cells alters cell growth

Abstract

DNA polymerase beta (β-pol) and its mRNA are maintained at constitutive levels during the cell cycle and during stages of cell growth in culture. To study biological consequences of variations in the level of this DNA repair enzyme and/or its mRNA, we prepared expression vectors in which cDNA for human β-pol is inserted under the control of a metallothionein promoter (pMT) in the sense and antisense orientation, respectively, and these vectors then were used for stable transformation of mouse 3T3 cells. Vectors also contained the mouseDHFR gene, such that culture of transformants in medium with increasing concentrations of methotrexate resulted in amplification of inserted DNA. The levels of sense and antisense transcripts are strongly increased by culture of transformants in medium with 65 µM Zn²⁺, although some expression is detected even without Zn²⁺ induction. After five days of induction, the β-pol level was about threefold higher in sense cells and about 10-fold lower in antisense cells than in parallel cultures without induction. The antisense line has a threefold increased cell doubling time in the presence of 65 µM Zn²⁺ compared with the absence of Zn²⁺. Zn²⁺ (65 µM) induction for the sense line results in normal growth for the first three days and, thereafter, a complete cessation of growth. Yet, these blocked cells remain fully viable. The results indicate that sudden deregulation of β-pol expression alters cell growth in mouse 3T3 cells.