• Open Access

Senescence-associated β-galactosidase is lysosomal β-galactosidase

Authors



Daniel DiMaio, Department of Genetics, Yale University School of Medicine, PO Box 208005, New Haven, CT 06520-8005, USA. Tel.: 203-785-2684; fax: 203-785-6765; e-mail: daniel.dimaio@yale.edu, Eun Seong Hwang, Department of Life Science, University of Seoul, Dongdaemungu, Jeonnongdong, Seoul, Korea 130-743. Tel.: 82-2-2210-2608; fax: 82-2-2210-2888 e-mail: eshwang@uos.ac.kr

Summary

Replicative senescence limits the proliferation of somatic cells passaged in culture and may reflect cellular aging in vivo. The most widely used biomarker for senescent and aging cells is senescence-associated β-galactosidase (SA-β-gal), which is defined as β-galactosidase activity detectable at pH 6.0 in senescent cells, but the origin of SA-β-gal and its cellular roles in senescence are not known. We demonstrate here that SA-β-gal activity is expressed from GLB1, the gene encoding lysosomal β-D-galactosidase, the activity of which is typically measured at acidic pH 4.5. Fibroblasts from patients with autosomal recessive GM1-gangliosidosis, which have defective lysosomal β-galactosidase, did not express SA-β-gal at late passages even though they underwent replicative senescence. In addition, late passage normal fibroblasts expressing small-hairpin interfering RNA that depleted GLB1 mRNA underwent senescence but failed to express SA-β-gal. GLB1 mRNA depletion also prevented expression of SA-β-gal activity in HeLa cervical carcinoma cells induced to enter a senescent state by repression of their endogenous human papillomavirus E7 oncogene. SA-β-gal induction during senescence was due at least in part to increased expression of the lysosomal β-galactosidase protein. These results also indicate that SA-β-gal is not required for senescence.

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