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Serum-responsive expression from the murine thymidine kinase promoter is specifically disrupted in a transformed cell

D W Bradley1, J L Fridovich-Keil, J M Gudas

  • 1Dana-Farber Cancer Institute, Division of Cell Growth and Regulation, Boston, Massachusetts 02115.

Cell Growth & Differentiation : the Molecular Biology Journal of the American Association for Cancer Research
|October 1, 1994
PubMed

Insights

In normal cells, thymidine kinase (TK) gene expression is tightly regulated. However, in transformed cells, TK regulation shifts to the posttranscriptional level, bypassing promoter control.

Area of Science:

  • Molecular Biology
  • Cell Cycle Regulation
  • Gene Expression

Background:

  • Thymidine kinase (TK) gene expression is crucial for cell cycle progression, particularly during the G1-S phase transition.
  • Normal cells exhibit tight transcriptional and posttranscriptional control of TK mRNA levels, leading to significant induction during the S phase.
  • Transformed cells show constitutive binding of the Yi protein complex to the TK promoter, yet still display S-specific TK mRNA induction, posing a regulatory question.

Purpose of the Study:

  • To investigate the differential regulation of thymidine kinase (TK) gene expression in transformed versus nontransformed cells.
  • To determine the role of promoter-mediated transcriptional control versus posttranscriptional mechanisms in TK gene regulation within the context of cellular transformation.
  • To elucidate the regulatory status of TK gene expression in transformed cells, specifically addressing the discrepancy between Yi protein binding and mRNA induction.

Main Methods:

  • Utilized cell synchrony experiments to analyze gene expression patterns across the cell cycle.
  • Employed stable transfection of both transformed and nontransformed cells with a TK promoter-beta-globin reporter gene construct.
  • Assessed reporter gene expression and correlated it with Yi DNA-binding activity.

Main Results:

  • Reporter gene expression was tightly regulated in nontransformed cells, mirroring normal TK gene control.
  • In contrast, reporter gene expression in transformed cells was constitutive, closely paralleling Yi DNA-binding activity.
  • These findings indicate a divergence in TK gene regulation between normal and transformed cells.

Conclusions:

  • Transformed cells exhibit a shift in thymidine kinase (TK) gene regulation, with promoter-mediated control becoming largely bypassed.
  • Posttranscriptional mechanisms appear to be the predominant regulatory pathway for endogenous TK in transformed cells.
  • The study supports the hypothesis that differential regulation of TK transcriptional and posttranscriptional control contributes to cellular transformation.

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