Calcium and S100B Regulation of p53-Dependent Cell Growth Arrest and Apoptosis

ABSTRACT

In glial C6 cells constitutively expressing wild-type p53, synthesis of the calcium-binding protein S100B is associated with cell density-dependent inhibition of growth and apoptosis in response to UV irradiation. A functional interaction between S100B and p53 was first demonstrated in p53-negative mouse embryo fibroblasts (MEF cells) by sequential transfection with the S100B and the temperature-sensitive p53Val135 genes. We show that in MEF cells expressing a low level of p53Val135, S100B cooperates with p53Val135 in triggering calcium-dependent cell growth arrest and cell death in response to UV irradiation at the nonpermissive temperature (37.5°C). Calcium-dependent growth arrest of MEF cells expressing S100B correlates with specific nuclear accumulation of the wild-type p53Val135 conformational species. S100B modulation of wild-type p53Val135 nuclear translocation and functions was confirmed with the rat embryo fibroblast (REF) cell line clone 6, which is transformed by oncogenic Ha-ras and overexpression of p53Val135. Ectopic expression of S100B in clone 6 cells restores contact inhibition of growth at 37.5°C, which also correlates with nuclear accumulation of the wild-type p53Val135 conformational species. Moreover, a calcium ionophore mediates a reversible G₁ arrest in S100B-expressing REF (S100B-REF) cells at 37.5°C that is phenotypically indistinguishable from p53-mediated G₁arrest at the permissive temperature (32°C). S100B-REF cells proceeding from G₁ underwent apoptosis in response to UV irradiation. Our data support a model in which calcium signaling and S100B cooperate with the p53 pathways of cell growth inhibition and apoptosis.

ACKNOWLEDGMENTS

We thank A. M. Chinn and R. Griffin for critical reading of the manuscript, R. Kuwano (Niigata University, Niigata, Japan) for providing human S100B cDNA, E. Gottlieb and M. Oren for providing recombinant p53Val135 retrovirus and clone 6 cells, Paul Andreassen for providing p53^−/− MEF, H. Y. Peng for help in constructing the S100B plasmid, D. Grunwald for FACS analysis, and B. Justine and B. Clemence for stimulating discussions.

This work was supported by grants from Association pour la Recherche sur le Cancer and Ligue National Contre le Cancer to J.B.