Re: Prognostic significance of a short sequence insertion in the MCL-1 promoter in chronic lymphocytic leukemia.

A recent article entitled " Prognostic Signifi cance of a Short Sequence Insertion in the MCL-1 Promoter in Chronic Lym-phocytic Leukemia " identifi ed two novel sequence variants of the MCL-1 promoter within lymphocytes from chronic lym-phocytic leukemia (CLL) patients but not within noncancerous tissue from the same individuals or in lymphocytes from 18 healthy control subjects (1). This result suggested that the variants — insertions of 6 and 18 nucleotides at position − 188 relative to the transcription start site as mapped by Akgul et al. (2) — were CLL-related somatic oncogenic mutations. Moshynska et al. (1) also determined that the 6-and 18-nucleotide insertions were associated with higher MCL-1 mRNA and protein expression. In the course of analyzing the E2F1-mediated transcriptional repression of MCL-1 (3 , 4) , we independently identi-fi ed and cloned the three observed sequence variants from three human cancer cell lines, H1299 (Mcl-1 +0/+0) lung cancer cells, K562 (Mcl-1 +6/+6) erythro-leukemia cells, and T98G (Mcl-1 +0/+18) glioblastoma cells, representing the MCL-1 +0, +6, and +18 alleles, respectively (see Supplemental Material at We next used polymerase chain reaction (PCR), followed by resolution of the PCR products on acrylamide gels, to determine MCL-1 promoter status in a large number of cell lines and solid tumors. The +6 and +18 promoters occurred with a high frequency in both breast and lung cancer genomic DNA (Fig. 1A). To determine if these variants were somatic in origin, we analyzed DNA derived from 15 sets of paired lung cancer and adjacent normal lung tissue from patients undergoing routine thoracotomy for surgical resection of their malignancy. All samples were provided in deidentifi ed fashion, and all patients provided informed consent as approved by the Institutional Review Board. In every instance, the MCL-1 promoter profi le was identical in cancerous and normal tissue (Fig. 1B and data not shown). To address the possibility that the MCL-1 promoter variants may predispose to malignancy, we screened DNA samples derived from 59 healthy individuals, all of whom had provided informed consent, for the presence of the MCL-1 promoter insertions. Nearly half of the total alleles had one or both insertions , and the insertion alleles were present at frequencies similar to those in cancer cell lines (Fig 1, A and C , and data not shown). Thus, it appears likely that the +6 and +18 MCL-1 promoter variants are common benign polymorphisms. MCL-1 belongs to the …