Overexpression of Separase induces aneuploidy and mammary tumorigenesis

Abstract

A neuploidy (aberrant chromosome number) is a hallmark feature of human malignancies (1, 2) and has also been proposed as a necessary event for tumorigenesis (2). Although there have been many proposed hypotheses, there is no general agreement as to why aneuploidy is so highly prevalent in cancer cells, and how it contributes to tumor progression (3, 4). Importantly, if aneuploidy forms an underlying cause of human cancer, it has not been fully substantiated. The mechanisms of aneuploidy also remain a fundamental unresolved problem in cancer biology.To understand how aneuploidy might originate in mammalian tissues, we have focused on the elements that regulate chromosomal segregation, particularly those involved in sister chromatid cohesion and separation, because chromosome missegregation, for example during mitosis, can lead to aneuploidy. A key gene in our analysis is ESPL1, which encodes an endopeptidase called Separase that separates sister chromatids by cleaving cohesin Rad21/Mcd1/Scc1 during the metaphase to anaphase transition. The hypothesis we tested is that hormonal stimulation of the p53-null mouse mammary gland results in misexpression of the ESPL1 gene, thus promoting aneuploidy and breast cancer formation. Dysregulation of the mitotic machinery that helps maintain chromosomal stability in mammary cells can result in aneuploidy and subsequently, cancer formation. We focused on Separase for the following reasons that have important implications for breast cancer: (i) Separase plays a central role in promoting faithful chromosome segregation; (ii) our previous studies strongly indicated that hormonal stimulation of p53-null mice mammary gland results in overexpression of the ESPL1 and Separase protein, which may be a direct cause of aneuploidy (5); and (iii) siRNA-mediated knockdown of Separase and Separase deficient mouse embryonic fibroblasts results in genomic instability (6-8).An evolutionarily conserved protein complex called cohesin and an endopeptidase named Separase play pivotal roles in the accurate segregation of sister chromatids into two daughter cells. Cohesion along the length of the sister chromatids is formed during DNA replication in S phase. Cohesion along the chromosomal arms is removed during prophase and from centromeric regions at the metaphase-to-anaphase transition when Separase is activated after its inhibitory chaperone securin is degraded (9, 10).To understand how aberration in sister chromatid separation may contribute to chromosomal missegregation, we investigated the role of Separase overexpression in mouse mammary cells by using a mammary epithelial transplant model (11) as well as various biochemical and functional assays. Our results indicate that conditional overexpression of Separase alone in mammary epithelial cells with a p53 mutant background is sufficient to induce aneuploidy and tumorigenesis in vitro and in vivo. Results Conditional Expression of Mouse Separase (mSeparase) Results inAneuploidy in Mouse Mammary Epithelial Cells. To examine the direct effect of ...

DNA-dependent cohesin cleavage by separase

“…Notably, both overexpression and mutations in separase have been shown to lead to an increased incidence of cancerous growth. 8,9 Thus, timely separation of sister chromatids is clearly essential for genomic stability.…”

The expanding universe of cohesin functions: a new genome stability caretaker involved in human disease and cancer

“…The overexpression of WAPL correlates with the progression of cervical cancer malignancy (Table 1), and cells overexpressing WAPL develop tumors after injection into nude mice [Oikawa et al, 2004]. Separase is found to be significantly overexpressed in human breast cancer [Zhang et al, 2008b], osteosarcoma and prostate cancer (Table 1) [Meyer et al, 2009]. Its induction leads to premature separation of chromatids, lagging chromosomes with specific chromosome aneuploidies [Zhang, et al, 2008b].…”

“…Separase is found to be significantly overexpressed in human breast cancer [Zhang et al, 2008b], osteosarcoma and prostate cancer (Table 1) [Meyer et al, 2009]. Its induction leads to premature separation of chromatids, lagging chromosomes with specific chromosome aneuploidies [Zhang, et al, 2008b]. Finally, ESCO2 is up-regulated in more aggressive melanomas [Ryu et al, 2007], Securin (also known as proto-oncogene pituitary tumor transforming gene, PTTG) is overexpressed in pituitary tumors [Zou et al, 1999] and RAD21 is overexpressed in breast [Atienza et al, 2005;Oishi et al, 2007] and prostate cancer (Table 1) [Porkka et al, 2004].…”

“…The overexpression of WAPL correlates with the progression of cervical cancer malignancy (Table 1), and cells overexpressing WAPL develop tumors after injection into nude mice [Oikawa et al, 2004]. Separase is found to be significantly overexpressed in human breast cancer [Zhang et al, 2008b], osteosarcoma and prostate cancer (Table 1) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 Cancer is thought to be a multistep process in which abnormalities in proto-oncogenes and tumor suppressors predispose cells to the acquisition of many other genetic changes which are responsible for the acquisition of the full malignant phenotype. Cohesin could play an important role in genome instability and tumorigenesis, and chromosome aneuploidy due to defects in correct chromosome segregation could cause the loss of heterozygosity of tumor suppressor genes or the improper activation of proto-oncogenes.…”

Regulation of the final stage of mitosis by components of the pre-replicative complex and a polo kinase

“…Defects in chromosomal segregation in somatic cells often lead to aneuploidy associated with abnormal development and tumorigenesis. [38][39][40] Chromosomal segregation is controlled by separase activity, which cleaves cohesin, leading to sister chromosome separation. 41 Premature activation of separase and chromosomal missegregation are prevented by multiple inhibitory mechanisms.…”