Pro-Apoptotic Role of the Human Gene Identified by Functional Complementation of a Yeast Δ Mutation.

To examine the pro-apoptotic role of the human ortholog (YPEL5) of the Yippee protein, the cell viability of mutant strain with deleted , the yeast ortholog, was compared with that of the wild-type (WT)- strain after exposure to different apoptogenic stimulants, including UV irradiation, methyl methanesulfonate (MMS), camptothecin (CPT), heat shock, and hyperosmotic shock. The Δ mutant exhibited enhanced cell viability compared with the WT- strain when treated with lethal UV irradiation, 1.8 mM MMS, 100 µ CPT, heat shock at 50°C, or 1.2 M KCl. At the same time, the level of Moh1 protein was commonly up-regulated in the WT- strain as was that of Ynk1 protein, which is known as a marker for DNA damage. Although the enhanced UV resistance of the Δ mutant largely disappeared following transformation with the yeast gene or one of the human genes, the transformant bearing pYES2- was more sensitive to lethal UV irradiation and its UV sensitivity was similar to that of the WT- strain. Under these conditions, the UV irradiation-induced apoptotic events, such as FITC-Annexin V stainability, mitochondrial membrane potential (ΔΨm) loss, and metacaspase activation, occurred to a much lesser extent in the Δ mutant compared with the WT- strain and the mutant strain bearing pYES2- or pYES2-. These results demonstrate the functional conservation between yeast Moh1 and human YPEL5, and their involvement in mitochondria-dependent apoptosis induced by DNA damage.