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

Abstract

Background: Mcl-1 protein contributes to the longevity of chronic lymphocytic leukemia (CLL) B cells, and its higher expression has been associated with resistance to chemotherapy. We sought structural changes in the MCL-1 gene in CLL patients and associated these with clinical parameters of the disease. Methods: The MCL-1 gene from peripheral blood lymphocytes from 58 CLL patients and 18 control subjects and from the RL and BC-3 lymphoma cell lines was sequenced. Mcl-1 mRNA expression (in 20 consecutive patients and four control subjects) was analyzed by RNase protection assay, and Mcl-1 protein expression (in 18 consecutive patients and four controls) was analyzed by western blotting. Genetic changes in MCL-1 were associated with biochemical and clinical characteristics, including expression of CD38, a negative prognostic factor. Cox proportional hazards modeling was used to determine the prognostic importance of changes in the MCL-1 gene, and the Kaplan-Meier method was used to analyze patient survival. All statistical tests were two sided. Results: A 6- or 18-nucleotide sequence insertion was found in the same site in the MCL-1 promoter in 17 of 58 patients and in BC-3 cells; it was absent in all control subjects and in RL cells. Of 21 CD38-negative patients, 10 had a promoter insertion; of 17 CD38-positive patients, one had a promoter insertion (P = .0099). Patients with a promoter insertion had higher mRNA (median = 26.8 relative units, interquartile range [IQR] = 14.9 to 35.2, versus median = 8.8 relative units, IQR = 3.9 to 15.7, P = .030, U-test) and protein (median = 0.84 relative units, IQR = 0.81 to 1.0 versus median = 0.47, IQR = 0.32 to 0.70, P = .021, U-test) expression, more rapid disease progression (P = .012), poorer response to chemotherapy (P = .001), and shorter overall (P = .0088) and disease-specific (P < .001) survival than patients with a normal promoter. The presence of an MCL-1 promoter insertion had prognostic significance in a Cox model (P = .001). Conclusions: The MCL-1 promoter insertion may identify a high-risk group of CD38-negative CLL patients. © Oxford University Press 2004, all rights reserved.