Identification and characterization of genes responsive to apoptosis: application of DNA chip technology and mRNA differential display.

Apoptosis (programmed cell death) is a genetically programmed active cell death process for maintaining homeostasis under physiological conditions and for responding to various stimuli. Many human diseases have been associated with either increased apoptosis (such as AIDS and neurodegenerative disorders) or decreased apoptosis (such as cancer and autoimmune disorders). In an attempt to understand apoptosis signaling pathway and genes associated with apoptosis, we established two cell model systems on which apoptosis is induced either by DNA damaging agent, etoposide or by redox agent, 1,10-phenanthroline (OP). DNA chip profiling or mRNA differential display (DD) was utilized to identify genes responsive to apoptosis induced by these two agents. In etoposide model with chip hybridization, we defined signaling pathways that mediate apoptosis in p53 dependent manner (through activation of p53 target genes such as Waf-1/p21, PCNA, GPX, S100A2 and PTGF-beta) as well as in p53-independent manner (through activation of ODC and TGF-beta receptor, among others). In OP model with DD screening, we cloned and characterized two genes: glutathione synthetase, encoding an enzyme involved in glutathione synthesis and Sensitive to Apoptosis Gene (SAG), a novel evolutionarily conserved gene encoding a zinc RING finger protein. Both genes appear to protect cells from apoptosis induced by redox agents. Further characterization of SAG revealed that it is a growth essential gene in yeast and belongs to a newly identified gene family that promotes protein ubiquitination and degradation. Through this activity, SAG regulates cell cycle progression and many other key biological processes. Thus, SAG could be a valid drug target for anti-cancer and anti-inflammation therapies.