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Differential occurrence of CSF-like activity and transforming activity of Mos during the cell cycle in fibroblasts

K Okazaki1, M Nishizawa, N Furuno

  • 1Division of Molecular Genetics, Kurume University, Fukuoka, Japan.

The EMBO Journal
|July 1, 1992
PubMed

Insights

The Xenopus c-mos proto-oncogene (Mosxe) arrests oocytes via cytostatic factor (CSF) activity. Its transforming activity, however, occurs in the G1 phase, distinct from its CSF role.

Area of Science:

  • Molecular Biology
  • Cell Cycle Regulation
  • Oncogenesis

Background:

  • The Xenopus c-mos proto-oncogene product, Mosxe, is known for its cytostatic factor (CSF) activity, arresting oocytes in metaphase II.
  • Mosxe also exhibits weak transforming activity in NIH3T3 cells, suggesting a role beyond oocyte maturation.

Purpose of the Study:

  • To investigate the relationship between Mosxe's cytostatic factor (CSF) activity and its transforming potential.
  • To determine the specific phase of the cell cycle at which Mosxe exerts its transforming activity.

Main Methods:

  • Creation and analysis of Mosxe mutants with altered N-terminal amino acids to assess transforming activity.
  • Construction and study of cyclin-Mosxe fusion proteins with varying stability during the M-G1 transition.
  • Observation of cell cycle progression (G2-M, G1, S phase) in transformed NIH3T3 cells under different serum conditions.

Main Results:

  • Mosxe mutants with stabilized penultimate N-terminal amino acids showed strong transforming activity and G2-M phase retardation, likely via CSF activity.
  • A stable cyclin-Mosxe fusion protein transformed cells more efficiently than an unstable one.
  • Cells transformed by unstable cyclin-Mosxe exhibited delayed S phase entry in low serum, unlike cells with stable cyclin-Mosxe.

Conclusions:

  • The transforming activity of Mosxe is distinct from its physiological CSF activity.
  • Mosxe's transforming activity is primarily exerted during the G1 phase of the cell cycle.

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