Telomerase activity in hybrids between telomerase-negative and telomerase-positive immortal human cells is repressed in the different complementationgroups but not in the same complementation group of immortality

The expression of telomerase is essential for cells to be immortalized, and most immortal cell lines possessed telomerase activity. Using the cell fus ion technique, it has been shown that mortal and telomerase-negative phenot ypes of normal cells are dominant over immortal and telomerase-positive phe notypes, suggesting that the normal cells possessed dominant repressor-type activity for telomerase expression. Several telomerase-negative immortal h uman cell lines were reported, in which telomerase-independent mechanisms w as supposed to maintain telomere length. We aimed at seeing whether the tel omerase-negative phenotype of these immortal cells is dominant over telomer ase-positive phenotype of other immortal cells in correlation with cellular mortality. Results showed that, when telomerase-positive and -negative imm ortal parental cell lines belonging to the different complementation groups were fused, telomerase-negative mortal hybrid clones arose, i.e. telomeras e-negative phenotype was dominant as well as mortal phenotype. However, whe n immortal hybrid cells arose from telomerase-positive and -negative immort al parents belonging to either the same or different complementation groups , they were all telomerase-positive, i.e. telomerase-negative phenotype app eared to be recessive. Telomerase-negative immortal hybrid was never establ ished from any combinations between telomerase-negative and -positive immor tal parental cells. (C) 1999 Elsevier Science Ireland Ltd. All rights reser ved.