Gene dosage effects in chronic lymphocytic leukemia

To understand the influence of chromosomal alterations on gene expression in a genome-wide view, chromosomal imbalances detected by single nucleotide polymorphism (SNP) chips were compared with global gene expression in 16 cases of chronic lymphocytic leukemia (CLL). A strong concordance between chromosomal gain or loss and increased or reduced expression of genes in the affected regions was found, respectively. Regions of uniparental disomy (UPD) were rare and had usually no consistent influence on gene expression, but in one instance, a large UPD was associated with a downregulation of most genes in the affected chromosome. The frequently deleted miRNAs, MIRN15A and MIRN16-1, did not show a reduced expression in cases with monoallelic deletions. The BCL2 protein, considered to be downregulated by these miRNAs, was upregulated not only in CLL with biallelic deletion of MIRN15A and MIRN16-1, but also in cases with monoallelic deletion. This suggests a complex regulation of BCL2 levels in CLL cells. Taken together, in CLL, a global gene dosage effect exists for chromosomal gains and deletions and in some instances for UPDs. We did not confirm a consistent correlation between MIRN15A and MIRN16-1 expression levels and BCL2 protein levels, indicating a complex regulation of BCL2 expression.