Normal p53 Function in Primary Cells Deficient for Siah Genes

Abstract

Overexpression studies have suggested that Siah1 proteins may act as effectors of p53-mediated cellular responses and as regulators of mitotic progression. We have tested these hypotheses using Siah gene knockout mice. Siah1a and Siah1b were not induced by activation of endogenous p53 in tissues, primary murine embryonic fibroblasts (MEFs) or thymocytes. Furthermore, primary MEFs lacking Siah1a, Siah1b, Siah2, or both Siah2 and Siah1a displayed normal cell cycle progression, proliferation, p53-mediated senescence, and G₁ phase cell cycle arrest. Primary thymocytes deficient for Siah1a, Siah2, or both Siah2 and Siah1a, E1A-transformed MEFs lacking Siah1a, Siah1b, or Siah2, and Siah1b-null ES cells all underwent normal p53-mediated apoptosis. Finally, inhibition of Siah1b expression in Siah2 Siah1a double-mutant cells failed to inhibit cell division, p53-mediated induction of p21 expression, or cell cycle arrest. Our loss-of-function experiments do not support a general role for Siah genes in p53-mediated responses or mitosis.

We thank Fiona Christensen for blastocyst injections, Patrick Humbert for fetal liver reconstitution experiments, Nadia Traficante for assistance with generation of MEFs, Dobrila Nesic and Paul Orban for providing reagents, and Helena Richardson, Patrick Humbert, and members of the Bowtell lab for critical reading of the manuscript and helpful discussions.

This work was supported by grants from the NHMRC. I.J.F. is a Grimwade Scholar (University of Melbourne); A.R.C. and M.O. are a Fellow and a Scholar, respectively, of the Leukemia and Lymphoma Society.