Prognostic significance of a short sequence insertion in the MCL-1 promoter in chronic lymphocytic leukemia.
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.
Moshynska
Oksana
O
Department of Pathology, Royal University Hospital and College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
Sankaran
Koravangattu
K
Pahwa
Punam
P
Saxena
Anurag
A
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015153:Blotting, Western; D016022:Case-Control Studies; D002878:Chromosomes, Human, Pair 1; D004251:DNA Transposable Elements; D004273:DNA, Neoplasm / Q000032:analysis; D018450:Disease Progression; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D015321:Gene Rearrangement; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000175:diagnosis / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000235:genetics*; D011237:Predictive Value of Tests; D011379:Prognosis; D011401:Promoter Regions, Genetic; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D017422:Sequence Analysis, DNA; D016019:Survival Analysis; D015854:Up-Regulation
D004251:DNA Transposable Elements; D004273:DNA, Neoplasm; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger