ENDOGENOUS BETA-GALACTOSIDASE ACTIVITY IN CONTINUOUSLY NONPROLIFERATING CELLS

Cytochemically detectable activity of endogenous beta-galactosidase wa s found at pH 6.0 in Swiss 3T3 cells after long-term incubation in low serum or in the presence of heparin concentrations known to reversibl y inhibit cell proliferation, A high percentage of beta-galactosidase- positive cells were detected in U937 and HL60 cultures at the late sta ge of macrophage-like differentiation induced by TPA, Interestingly, a small number of beta-galactosidase-positive cells were found even in the growing Swiss 3T3 cultures. These positive cells expressed morphol ogical features similar to those of senescent cells. Thus, the activit y of beta-galactosidase at pH 6.0 cannot be considered an exclusive ma rker of senescent cells since it is expressed in other types of nonpro liferating cells. (C) 1998 Academic Press.