Abstract 2247: Histone H3 cleavage via Cathepsin L drives a cellular senescence program

Abstract

Abstract Oncogene-induced senescence (OIS) is characterized by irreversible loss of proliferative capacity. It has been proposed that OIS functions as a tumor suppressor mechanism, and several studies have demonstrated induction of senescence markers in pre-malignant lesions. In addition to profound morphological changes, significant alterations in chromatin structure occur during senescence including formation of senescence-associated heterochromatin foci (SAHF). We have used well-characterized senescence models in human primary lung fibroblasts and melanocytes to study how chromatin alterations contribute to the senescence phenotype. We discovered that the N'-terminal tail of histone H3 is proteolytically cleaved by the lysosomal protease Cathepsin L1 (CTSL1). We show that CTSL1 is induced during senescence both at the mRNA and protein levels, and that it is present in the chromatin fraction of senescent cells. Chemical and shRNA-mediated inhibition of CTSL1 activity effectively block H3 tail cleavage and leads to a SAHF formation defect. We identified two distinct cleaved forms of H3 in senescent cells, which are associated with chromatin and incorporated into nucleosomes. Using antibodies directed against specific post-translational modifications (PTMs) of the histone H3 tail, we have mapped the approximate locations of the cleavage sites. Furthermore, overexpression of flag-tagged cleaved versions of H3, but not the full-length histone, trigger robust senescence in IMR90 cells accompanied by a modest induction of SAHFs. Interestingly, we also detect cleaved H3 in chromatin extracted from benign nevi tissue samples, providing evidence of H3 tail cleavage in senescence models in vivo. Collectively, our results suggest that H3 tail cleavage may contribute significantly to the senescence phenotype, potentially through transcriptional regulation of key senescence target genes. This area of investigation is currently ongoing. Citation Format: Luis F. Duarte, Andrew R. Young, Hsan-Au Wu, Taniya Panda, Zichen Wang, Alexandre G. Maia, Dan Hasson, Avnish Kapoor, Masashi Narita, Emily Bernstein. Histone H3 cleavage via Cathepsin L drives a cellular senescence program. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2247. doi:10.1158/1538-7445.AM2014-2247