BCL-XL Mediates the Strong Selective Advantage of a 20q11.21 Amplification Commonly Found in Human Embryonic Stem Cell Cultures

Abstract

SummaryHuman embryonic stem cells (hESCs) regularly acquire nonrandom genomic aberrations during culture, raising concerns about their safe therapeutic application. The International Stem Cell Initiative identified a copy number variant (CNV) amplification of chromosome 20q11.21 in 25% of hESC lines displaying a normal karyotype. By comparing four cell lines paired for the presence or absence of this CNV, we show that those containing this amplicon have higher population doubling rates, attributable to enhanced cell survival through resistance to apoptosis. Of the three genes encoded within the minimal amplicon and expressed in hESCs, only overexpression of BCL2L1 (BCL-XL isoform) provides control cells with growth characteristics similar to those of CNV-containing cells, whereas inhibition of BCL-XL suppresses the growth advantage of CNV cells, establishing BCL2L1 as a driver mutation. Amplification of the 20q11.21 region is also detectable in human embryonal carcinoma cell lines and some teratocarcinomas, linking this mutation with malignant transformation.

Low-grade chromosomal mosaicism in human somatic and embryonic stem cell populations

“…This might indicate that most of the CNVs are selected against due to deleterious effects for the cells. However, VUB02 passage 351 does contain the 20q11.21 amplification, which is known to provide a survival advantage 9,10 . This indicates that CNVs that start as a single-cell event can clonally take over the culture.…”

“…More recently, the group of Abyzov et al 6 made use of the clonal nature of humaninduced pluripotent stem cells (hiPSCs) to show that human skin fibroblasts are highly mosaic, with up to 30% of cells carrying copy number variants (CNVs). In the field of human pluripotent stem cell research, a large number of studies have shown that human embryonic stem cell (hESC) cultures are frequently taken over by chromosomally abnormal cells 7,8 , most probably because of a selective advantage caused by the chromosomal aberration 9,10 . Conversely, not much is known on how frequently hESC spontaneously mutate, either through abnormal chromosome segregation or by acquiring small amplifications or deletions, nor on the nature of these changes.…”

The molecular characteristics of colorectal cancer: Implications for diagnosis and therapy (Review)

“…Previously, BCL2 like 1 (BCL2L1), which is located in the smallest common chromosomal region of gain and regulates the mitochondrial apoptotic pathway, has been confirmed as the key-driver gene of this amplification (37,38). Accordingly, the overexpression of Bcl-xL, an anti-apoptotic isoform of BCL2L1 has offered cells a survival advantage by preventing apoptosis (37,38). Overexpression of this gene may also be responsible for the gain of 20q in various human cancer types (39).…”

White paper on guidelines concerning enteric nervous system stem cell therapy for enteric neuropathies

“…This was confirmed by trials in which cultures of diploid hPSC were spiked with a small proportion of karyotypically abnormal cellsthat then took over the cultures within a very few passages (Olariu et al, 2010). In the case of chromosome 20 gains it has been possible to identify a gene, BCL2L1 , that appears to drive the selective advantage by limiting apoptosis of hPSC during passaging (Avery et al, 2013; Nguyen et al, 2014). This gene lies in a short region of chromosome 20 that is subject to frequent amplification but often too short to be detected by standard G-banding karyotyping.…”