Tumor suppressor
p53 is the most frequently mutated gene in human cancer. It orchestrates the response to genotoxic and other stresses by arresting the cell cycle, activating repair of damaged DNA and/or promoting apoptosis. Although
p53 has been implicated in many other cellular processes, analysis in mammals is complicated by the existence of family members
p63 and
p73, which share some overlapping functions with
p53 but which also have distinct cellular roles. C. elegans has only one
p53 family member,
cep-1, which we previously found performs multiple roles in the germline and soma (Derry et al., 2001, Science, Vol. 294, 591). In the germline,
cep-1 is required for DNA damage-induced apoptosis and proper meiotic chromosome segregation, whereas in the soma it regulates environmental stress resistance. To understand how
cep-1 regulates these diverse cellular functions, we have undertaken a genome-wide RNAi screen to identify modifiers of a
cep-1 mutant. Using a strong loss-of-function allele,
cep-1(
gk138), we have identified several genes that modify
cep-1 activity. These modifiers include genes encoding a wide variety of protein families ranging from components of the transcription machinery to protein degradation. For example, we found that
cep-1(
gk138) mutants are resistant to the lethality induced by
ned-8(RNAi). NED-8 (Nedd8 in mammals) is a ubiquitin-like protein that regulates the localization and stability of a growing list of proteins. While
ned-8 RNAi results in over 90% lethality, this lethality is reduced to about 30% in a
cep-1(
gk138) mutant. Feeding
ned-8 dsRNA to worms carrying a
cep-1::CEP-1::GFP translational fusion reporter leads to an increased GFP signal in arrested embryos, suggesting that one function of NED-8 may be negative regulation of CEP-1 protein levels in the developing embryo. Other lethal genes that are rescued by
cep-1(
gk138) do not detectably affect the CEP-1::GFP signal, revealing multiple connections in the
cep-1 network. This screen has revealed the utility of applying functional genomics approaches to unraveling the complex genetic interactions through which tumor suppressor
p53 functions.