APOPTOSIS OF PREGNANCY-DEPENDENT MAMMARY-TUMOR AND TRANSPLANTABLE PREGNANCY-DEPENDENT MAMMARY-TUMOR IN MICE

Pregnancy-dependent mammary tumors (PDMT) of GR/A mice and transplanta ble PDMT (TPDMT-4 line) in DDD mice, are exceptionally stable in hormo ne dependence, continue to grow until parturition and regress soon aft er delivery. In order to study the regression mechanism of PDMT and TP DMT-4, morphological and biochemical changes were examined in the tumo rs removed on day 18 (TPDMT-4) or day 20 (PDMT) of pregnancy, and on t he expected parturient and the following postpartum days. DP;A fragmen tation occurred from day 18 (TPDMT-4) or day 20 (PDMT) of pregnancy to the day after parturition. Apoptotic cells were demonstrated by an in situ 3'-end labeling method, and the plateau of the number of apoptot ic cells was observed on the parturient day in PDMT and on the day aft er parturition in TPDMT-4. Reverse transcriptase polymerase chain reac tion showed that expression of Fas was slightly increased but that of bcl-2 was decreased during the process of involution of TPDMT-4 and PD MT. These results suggest that both an increase in expression of Fas a nd decrease in expression of bcl-2 are involved in the apoptosis of pr egnancy-dependent mammary tumor cells after parturition.