The role of p53 tumor suppresser gene and bcl-2 protooncogene in rat corpus luteum death

OBJECTIVE: The purpose of this study was to find out whether the mammalian corpus luteum undergoes genetically programmed cell death as evidenced by the positive or negative expression of specific biochemical markers of apoptosis (p53 and bcl-2). STUDY DESIGN: Twenty-six immature 28- day-old female Sprague-Dawley rats were given 10 IU of pregnant mare's serum gonadotropin to induce ovulation and corpus luteum formation. Corpora lutea were collected on postovulatory days 8, 10, 12, and 14 and snap-frozen immediately. Determinations of apoptotic fragmentation of deoxyribonucleic acid were performed with use of samples radiolabeled at 3'-ends with deoxynucleotide α-phosphorus 32-deoxycytidine triphosphate (3000 Cl/mmol). Transcription of p53 and bcl-2 was determined By Northern blot analysis of tote ribonucleic acid. Protein expression of p53 and bcl-2 was determined by Western blot analysis with a monoclonal rat antibody for p53 and a polyclonal rabbit antibody for bcl-2. RESULTS: The nuclear fragmentation assay revealed formation of oligonucleosomes resulting in typical laddering of the deoxyribonucleic acid (corpus luteum) consistent with programmed cell death. Northern blot analysis of total ribonucleic acid prepared from immature (28- day-old) rat corpus luteum revealed the presence of a single p53 messenger ribonucleic acid transcript (2.1 kb) in all ages of corpus luteum studied from day 8 to day 14. Western blot analysis for D53 revealed a gradual reduction in p53 protein in corpus luteum from day 8 to day 12 until it became undetectable on day 14. Western blotting revealed expression of specific protein for bcl-2. CONCLUSIONS: It appears that programmed cell death, as evidenced by formation of oligonucleosomes, occurs during mammalian luteal regression. The patterns of p53 ribonucleic acid expression in the corpus luteum suggest that the protein products of p53 and bcl-2 do not act in a diametric manner to regulate programmed cell death in the corpus luteum. The current results suggest that the mechanisms leading to programmed cell death in the mammalian corpus luteum may differ considerably from those in other organ systems.