Short Nucleotide Insertions in the MCL-1 Promoter Affect Its Gene Expression.

We have recently reported a short nucleotide (six and eighteen) insertion (6- and 18-nt) in the MCL-1 promoter (−190bp upstream of the major transcription start site, GenBank, AN: AF198614) in B-cell chronic lymphocytic leukemia patients. These insertions were found to be polymorphisms. CD38-negative CLL patients with these promoter insertions had higher mRNA levels, poor response to standard chemotherapy and shorter survival. The aim of the present study was to test the hypothesis that these insertions directly effect MCL-1 gene expression. K562 and HeLa cells were transfected with pGL3-Basic, pGL3-Control and four reporter plasmids were constructed with a +0/0, +6/6, +18/18, and −23/23 MCL-1 promoter linked to Luciferase. Firefly activity in each transfection was normalized to Renilla Luciferase activity. At 24-hours post-transfection cells were induced with phorbol 12-myristate 13-acetate (PMA), granulocyte-macrophage colony stimulating factor (GM-CSF), both PMA and GM-CSF, or with fresh media only. At 48-hours post-transfection cells were harvested and Dual-Luciferase Assay was performed. Compared to transfection with pGL3-(+0/0) plasmid, the Luciferase PMA-stimulated activity for K562 cells transfected with pGL3-(+6/6) and pGL3-(+18/18) was 1.7 (P=0.0277) and 1.5 times higher (P=0.0067) respectively, and for pGL3-(−23/23) was 3.2 times lower (P=0.0021). The Luciferase PMA-stimulated activity for HeLa cells transfected with pGL3-(+6/6) was 3.3 times higher (P=0.0038), pGL-3-(+18/18) was 2.3 times higher (P=0.0245), and did not differ significantly for pGL3-(−23/23), compared to pGL3-(+0/0). Similar results were observed for GM-CSF-stimulated activity for HeLa cells, where activity was 3.9 times (P=0.0068) for pGL3-(+6/6) and 2.5 times (P=0.0258) higher for pGL3-(+18/18). Unstimulated Luciferase activity was also 2.5 times higher (P=0.0115) for pGL3-(+18/18) compared to pGL3-(+0/0) plasmid. These results provide experimental evidence for the positive effect of these nucleotide insertions (6- and 18-nt) on MCL-1 gene expression in both hemopoietic (K562) and epithelial (HeLa) cells.