11q23 Deletion Is Associated with a Distinct Gene Expression Pattern

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[2480] 11q23 Deletion in B-Cell Chronic Lymphocytic Leukemia Is

Associated with a Distinct Gene Expression Pattern by cDNA Array and

Unique In Vitro Cell Proliferative Signature.

D. Dickinson, Lynette M. , M. Townley, Warren G.

Sanger, Philip J. Bierman, Shantaram S. Joshi Genetics, Cell Biology,

& Anatomy, University of Nebraska Medical Center, Omaha, NE, USA;

Deparment of Preventative and Societal Medicine, University of

Nebraska Medical Center, Omaha, NE, USA; Oncology, Hematology PC,

Methodist Hospital, Omaha, NE, USA; Department of Internal Medicine

Oncology & Hematology Section, University of Nebraska Medical Center,

Omaha, NE, USA

B-cell Chronic Lymphocytic Leukemia (B-CLL) is well characterized for

its clinical heterogeneity. One factor that influences time to

progression and treatment, as well as overall survival, is the

presence of chromosome aberrations. Deletions of 17p13 and 11q23 are

associated with shortened time to progression and lower overall

survival.

In this study, we identified chromosome aberrations by Fluorescent In

Situ Hybridization (FISH) from peripheral blood of 28 B-CLL patients.

Deletions of 13q was the most common chromosome abnormality with 10

patients (36%). 11q deletion was found at a slightly lower than

expected frequency with 4 patients (14%), followed by 7 (25%) Trisomy

12 patients, four (14%) 17p13 deletion patients, and three (11%) with

normal karyotype.

Gene expression profiling, with Clontech Apoptosis and Cell Cycle

cDNA arrays, was used to identify genes which best predict the

chromosome aberration. In particular, Cyclin Dependent Kinase 1

(CDK1) was found to be over-expressed in the 11q23 and 17p deletions.

CDK1 is associated with G2/M phase transition and cell proliferation.

Over-expression of this gene has been noted in other lymphoid

malignancies.

In contrast, Activator of Apoptosis Harakiri (HRK) was found to be

over-expressed in all members of the Trisomy 12 group relative to the

poor prognostic 11q and 17p deletion groups. HRK is a Bcl-2 family

member associated with apoptosis initiation. Its role in normal or

malignant B cells is not known. The expression levels of CDK1 and HRK

have been confirmed in 24 samples by Real-Time quantitative PCR

using -actin as a reference gene.

Unsupervised Hierarchical clustering reveals that B-CLL samples with

the 11q23 deletion group together and share a distinct gene

expression pattern involving over-expression of cell cycle related

genes and several caspases. Furthermore, based on the expression of

CDC2 and other cell cycle-related genes in the 11q23 deletion group

we monitored the proliferative state of 16 of the B-CLL samples by

flow cytometry using propidium iodide staining.

Cell cycle analysis revealed a pronounced G2/M phase peak in those

samples with the 11q deletion relative to other chromosome

aberrations. Finally, B-CLL samples with the 11q23 deletion showed

two to three fold increased proliferative capacity in vitro compared

to B-CLL cells with 13q deletion, Trisomy 12, or normal in response

to LPS mitogen stimulation by thymidine (3H) incorporation.

These results suggest that B-CLL cells from patients with 11q23

deletion are undergoing proliferation in the peripheral blood or

proliferating at a higher rate in the bone marrow and other

sequestered sites. This property may be responsible for the

aggressive behavior of this B-CLL subtype. This research was

supported by the U. Pardee Foundation, Midland, Michigan.