Abstract
Human embryonic stem cells (hESCs) gradually accumulate abnormal karyotypes during long-term suboptimal culture, which hinder their application in regenerative medicine. Previous studies demonstrated that the activation of CTNNB1 might be implicated in this process. Hence, the hESC line with stably silenced CTNNB1 was established to further explore the role of CTNNB1 in the malignant transformation of hESCs. It was shown to play a vital role in the maintenance of the physiological properties of stem cells, such as proliferation, migration, differentiation, and telomere regulation. Furthermore, the malignant transformation of hESCs was induced by continuous exposure to 0.001 μg/ml mitomycin C (MMC). The results showed that CTNNB1 and its target genes, including proto-oncogenes CCND1 and C-MYC, were aberrantly upregulated in hESCs after MMC treatment. Moreover, the high expression of CTNNB1 accelerated cell transition from G0/G1 phase to the S phase and stimulated the growth of cells containing breakage-fusion-bridge (BFB) cycles. Conversely, CTNNB1 silencing inhibited these effects and triggered a survival crisis. The current data indicated that CTNNB1 is intimately associated with the physiological properties of stem cells; however, the aberrant expression of CTNNB1 is involved in the malignant transformation of hESCs, which might advance the process by facilitating telomere-related unstable cell proliferation. Thus, the aberrant CTNNB1 level might serve as a potential biomarker for detecting the malignant transformation of hESCs.
Highlights
Human embryonic stem cells are derived from the inner cell mass of blastocysts with the potential of unlimited self-renewal and pluripotent differentiation that makes it a candidate source of cells for regenerative medicine [1]
We found that trace levels of mitomycin C (MMC), a DNA-damaging agent widely used for the preparation of feeder cells to support Human embryonic stem cells (hESCs) growth, remained in the culture system which might be a major cause of these abnormalities [7]
We demonstrated that CTNNB1 was aberrantly upregulated in karyotypically aberrant hESCs under suboptimal culture conditions
Summary
Human embryonic stem cells (hESCs) are derived from the inner cell mass of blastocysts with the potential of unlimited self-renewal and pluripotent differentiation that makes it a candidate source of cells for regenerative medicine [1]. Numerous studies have demonstrated that the accumulated chromosomal aberrations in long-term suboptimal cultured hESCs are similar to those found in tumorigenesis and might interfere with the clinical application [2,3,4]. Our previous studies found that the human embryonic stem cell line, chHES-3, gained increasing karyotypic abnormalities and progressed toward malignancy under long-term suboptimal culture in vitro [5, 6]. We found that trace levels of mitomycin C (MMC), a DNA-damaging agent widely used for the preparation of feeder cells to support hESC growth, remained in the culture system which might be a major cause of these abnormalities [7]. We demonstrated that CTNNB1 was aberrantly upregulated in karyotypically aberrant hESCs under suboptimal culture conditions. Under optimized culture conditions, hESCs with different passages maintained normal karyotype, and the expression of CTNNB1 did not display significant changes in karyotypically normal hESCs, thereby suggesting a link between CTNNB1 and the malignant transformation of hESCs [6]
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