KCNRG as tumor suppressor gene candidate in B-cell chronic lymphocytic leukemia and multiple myeloma

196 Multiple myeloma (MM) is a malignant disease originating from follicle center B-lymphocytes which differentiate to plasma cells accumulating in the bone marrow. Chromosome 13q14 harbor a critical tumor suppressor gene since deletion of 13q14 is a strong adverse prognostic indicator in MM. The same chromosomal region is deleted in chronic lymphocytic leukemia (CLL) patients. For both diseases, haploinsufficiency mode of tumor suppression has been proposed. Haploinsufficiency implies that mutation screening might be ineffective as a primary mean of search for MM and/or CLL tumor suppressor gene, as deletion of one copy of TSG is enough for tumor progression. We created a detailed map of transcripts located in 13q14 area and pinpointed KCNRG gene encoding potassium channel inhibitor protein as a primary candidate for MM/CLL TSG. KCNRG encodes a protein with a high homology to the tetramerization domain of voltage-gated K+ channels. This protein may interfere with the normal assembly of the K+ channel proteins, binding to their tetramerization domain and causing the suppression of Kv channels. Using the patch-clamp technique, we determined that KCNRG indeed suppresses Kv channel activity in the human prostate cell line LNCaP. Experiments producing stable overexpression of the KCNRG-L and KCNRG-S protein isoform in the model cell lines LNCaP, HL60 and RPMI8226 demonstrated significant suppression of their proliferation rates. We also observed changes in the phenotypes of the both stably and transiently transfected LnCaP and RPMI8226, particularly, multinucleated cells. There were also indications of an importance of the KCNRG-L in the process of cell adhesion and differentiation as after transfection, LNCaP cell line demonstrated more contact inhibition and does not grow as confluently as do the nontransfected cells. Apoptosis Caspase-Glo assays showed a significant 26% increase in apoptosis for transfected cells of RPMI8226 line. We also performed expression profiling of transfected and nontransfected cell lines and revealed that in the cells transfected with KCNRG the expression of genes related to cell cycle checkpoints and apoptosisis increased. Transfected RPMI8226 cells demonstrated a marked upregulation of TP53. Taken together, these data indicate that the human KCNRG gene might behave as a tumor suppressor via a decrease of Kv channel activity. As KCNRG is indeed haploinsufficient and one wild-type copy of the gene remains in tumor cells, it may be possible to boost its expression or the activity of its protein product to achieve a therapeutic effect. In addition to that, potassium-channel inhibitors could be used to simulate activity of intact KCNRG in tumor cells. The excellent track record of nanomolar concentrations of K+ channel blockers in the management of epilepsy, stroke, cardiac arrhythmias and high blood pressure enhances the attractiveness of this therapeutic approach.