Abstract
Mutations at the protein-coding region of TERT gene (chromosome 5p15.33) have been well characterized in patients affected by a constitutional telomere syndrome, including diskeratosis, aplastic anemia and pulmonary fibrosis (Calado RT, Hematology, ASH 2009:338). In rare cases somatic mutations may occur in de novo MDS/AML (Calado RT, Young NS. Blood 2008;111:4446). Mutations involving the regulatory region of TERT gene have been recently identified in a consistent proportion of familial and sporadic melanoma and in a subset of tumors originating from tissues with low rate of self-renewal (glioblastoma, liposarcoma, oligodendroglioma bladder cancer, upper urinary tract cancer). These mutations create new binding motifs for Ets/TCF transcription factors, thus increasing TERT gene transcription (Killela PJ et al, PNAS 2013;110:6021; Horn S et al, Science 2013;339:959). As far as we know TERT promoter mutations were never described in MDS.
Material and Methods
Index Case. A 52 years old woman was selected because of a complex phenotype including abnormal skin pigmentation, familial pulmonary fibrosis, osteoarthritis, and a refractory cytopenia with multilineage dysplasia (RCMD, WHO 2008) with a 47,XX,+8 karyotype.
Screening Cases. Mutational analysis was extended to a cohort of 115 patients (72 males; 44 females, median age 69) referred to the Laboratory of Cytogenetics, Hematology Department,University of Perugia, Italy.
Cytogenetics was normal in 49 cases (43%). Abnormalities included: isolated del(5q) (seven cases, 6%); del(5q) plus one additional change (three cases, 3%); isolated del(20q) (fourteen cases, 12%); trisomy 8 (five cases, 4%); monosomy 7 (two cases, 2%); -Y (three cases, 3%); del(11q) (two cases, 2%); complex karyotype (twenty-four cases, 21%); other aberrations (six cases, 5%).
Genomic DNA was extracted from bone marrow (BM) of all cases and from peripheral blood T lymphocytes of index case using Salting out method. In all cases TERT promoter was screened using PCR based DHPLC assay (Wave system; MD Transgenomic Inc. Omaha, NE). The 274bp amplicon was amplified with forward primer 5'GTCCTGCCCCTTCACCTTC3' and reverse primer 5'AGCACCTCGCGGTAGTGG3' using Robust Start Taq KAPA2G (Biosystems, Woburn, MA). DNA from abnormal elution profiles were re-amplified and sequenced by Sanger method (ABI 3500 Genetic Analyzer, Applied Biosystems). Variations were detected using Finch TV v. 1.4.0. In the index case 23 amplicons encompassing all 16 exons of TERT gene were also screened (NC_000005.9). Mutations cloning was carried out after RNA extraction (Trizol, Invitrogen, Life Technologies, Paisley, UK), reverse transcription (ThermoscriptTM RT-PCR System, Invitrogen) and amplification (TERT_2CF (5'-CAGCGCTACTGGCAAATGCG-3' Ta-61,4°C; and TERT_2543R (5'-GGCACTGGACGTAGGACTTG-3' Ta-61,4°C). PCR products were sub-cloned into pGEM-T easy vector (Promega, Madison, WI, USA) and sequenced.
Results
Index Case. Patient was a compound heterozygous for two germline variations: a nonsense mutation c.1209C>A p.C403* (exon 2) and a missense mutation c.2455C>T p.R819C (exon 8). A putative somatic A>C transition 57 bp before the ATG start codon was detected only in BM cells (Table).
Screening Cases. DHPLC analysis showed three patients (2.6%) with a two-peak elution profile. Sequencing revealed a 10 bp duplication (c.1-110_1-101) in case 2; a c.1-124 C>T point mutation in case 3; a point mutation c.1-78 C>T in case 4 (Table).
Comment
We showed that TERT gene promoter variations are recurrent events in 2.6% of MDS patients. Only low/int1 risk MDS (IPSS) were affected in this series. The c.1-57A>C, previously reported as a germline activating variation in familial melanoma (Horn S et al, Science 2013;339:959), was likely a somatic mutation in our index case, thus supporting its role in clonal MDS proliferation. We first found the melanoma activating c.1-124 C>T point mutation (Huang FW et al, Science 2013;339:957; Killela PJ et al, PNAS 2013;110:6021) in a MDS with isolated del(5q). The new variation of our case n.4 does not appear to introduce a new transcription factor binding site (http://www.cbrc.jp/research/db/TFSEARCH.html), whereas the 10bp duplication of case 2 indicates an hypothetical binding site for Ikaros. Further results from ongoing functional studies in these cases will be presented.
Disclosures:
No relevant conflicts of interest to declare.
Human TERT Promoter Mutations in Atypical and Anaplastic Meningiomas
