EXPRESSION PROFILE OF SENESCENCE-ASSOCIATED BETA-GALACTOSIDASE AND ACTIVATION OF TELOMERASE IN HUMAN OVARIAN SURFACE EPITHELIAL-CELLS UNDERGOING IMMORTALIZATION

Senescence is a specific physiological stage of cells characterized by long population doubling time. It accounts for the inability of norma l somatic cells to undergo indefinite cell division. As the number of population doublings increase, cell cycle regulatory mechanisms come i nto play and signal cells to exit the cell cycle and become senescent. Senescence has been implicated in the aging process and may function as a tumor suppressor mechanism in human cells. The ability to measure the degree of cellular senescence is important in understanding the b iological processes regulating cell aging and immortalization. Senesce nt cells exhibit an enzyme termed senescence-associated beta-galactosi dase (SA-beta-Gal) which is detected at pH 6.0 via histochemical stain ing. Cells immortalized by viral oncogenes often enter a stage of cris is at the early phase of immortalization. The cells at crisis have a l ong population doubling time. Cells at the crisis stage resemble senes cent cells and the expression of SA-beta-Gal may be used to monitor th e process of immortalization. In this study the expression profile of SA-beta-Gal was examined in human ovarian surface epithelial cells (HO SE 6-3) undergoing immortalization by the human papilloma viral oncoge ne E6 and E7 (HPV E6 and E7). Our results showed a low percentage (12. 0%) of HOSE 6-3 cells expressing SA-beta-Gal activity at the pre-crisi s stage. The percentage of HOSE 6-3 cells expressing SA-beta-Gal activ ity was highest (39.2%) at the crisis stage. When HOSE 6-3 cells achie ved immortalized status there was a sharp decrease in cells (1.3%) exp ressing SA-beta-Gal activity. In addition, an inverse relationship bet ween the expression of SA-beta-Gal activity and telomerase activity wa s noted in cells undergoing immortalization. The results confirm that the SA-beta-Gal enzyme is a good marker for monitoring the population of cells undergoing senescence at different stages of immortalization and that telomerase activation is a characteristic feature of post-cri sis cells.