A quantitative analysis of genomic instability in lymphoid and plasma cell neoplasms based on the PIG-A gene

Abstract

It has been proposed that hypermutability is necessary to account for the high frequency of mutations in cancer. However, historically, the mutation rate (μ) has been difficult to measure directly, and increased cell turnover or selection could provide an alternative explanation. We recently developed an assay for μ using PIG-A as a sentinel gene and estimated that its average value is 10.6 × 10 -7 mutations per cell division in B-lymphoblastoid cell lines (BLCLs) from normal donors. Here we have measured μ in human malignancies and found that it was elevated in cell lines derived from T cell acute lymphoblastic leukemia, mantle cell lymphoma, follicular lymphoma in transformed phase, and 2 plasma cell neoplasms. In contrast, μ was much lower in a marginal zone lymphoma cell line and 5 other plasma cell neoplasms. The highest μ value that we measured, 3286 × 10 -7 , is 2 orders of magnitude above the range we have observed in non-malignant human cells. We conclude that the type of genomic instability detected in this assay is a common but not universal feature of hematologic malignancies. IntroductionA model sentinel gene to measure spontaneous somatic mutations must be non-essential for growth or viability, and the mutant phenotype must be detectable among a vastly larger population of normal cells. Since a single mutation conferring loss of function could be complemented by the wild type allele on the homologous chromosome, most autosomal genes are not suitable for this purpose. However, due to hemizygosity in males and X-inactivation in females, a single mutation is sufficient to inactivate X-linked genes. For example, among lymphocytes in normal adults, resistance to 6-thioguanine occurs as a consequence of a spontaneous inactivating mutation in HPRT (Xq26-q27.2), at a frequency (f) of ∼ 2 -10 × 10 -6 [1].Corresponding author. David J. Araten, MD, NYU Cancer Center, 7 th Floor, 160 East 34 th Street, New York, NY 10016. 212-731-5186 (office); 212-731-5540 (fax). David.Araten@nyumc.org. There are no conflicts of interest to report.Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. While f represents the proportion of mutants within a population, the mutation rate (μ) represents the probability of a new mutation per cell division. If mutations are growth-neutral, f will increase over time according to the formula Δf = μ × Δd, where d represents number of cell divisions. By analysis of f values for HPRT in human population groups of different ages and estimates for Δd in human lymphocytes in vivo, it has been proposed that the normal μ value for this gene is ∼8.4 ×...

The rate of spontaneous mutations in human myeloid cells

“…This value is about 2 orders of magnitude above the mutant frequency in granulocytes from normal donors, and we believe that this represents a manifestation of widespread hypermutability across the genome, including the PIG-A gene. This is in keeping with our previous report that a large proportion of cell lines derived from hematologic malignancies demonstrate an elevated μ value [20]; in the KG-1 cell line, this may be due to a mutation in hOGG1 and a reduction in base excision repair [41]. …”

“…In B-lymphoblastoid cell lines (BLCLs) from normal individuals, we have reported that μ ranges from about 2.5 to 30 × 10 -7 mutations per cell division [14,15], which is similar to the results provided by Green et al [11], and it is elevated in a significant proportion of malignant cell lines [20]. Recently, we have shown an elevation in f in approximately 50% of ex vivo blast samples derived from children with ALL [21].…”

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“…The studies are summarized in table according to the year of publication. The studies can be broadly classified (classification indicated by letters in table ) into studies in cancer cells (A ), in cells from normal donors (B; ), in cells with impaired DNA damage response or DNA repair defects (C ), in human lymphocytes exposed to environmental stressors (D ) and recently also in the TK6 cell line that is widely used and relevant for chemical risk assessment (E ).…”