CBFB and MYH11 in inv(16)(p13q22) of acute myeloid leukemia displaying close spatial proximity in interphase nuclei of human hematopoietic stem cells.

To gain a better understanding of the mechanism of chromosomal translocations in cancer, we investigated the spatial proximity between CBFB and MYH11 genes involved in inv(16)(p13q22) found in patients with acute myeloid leukemia. Previous studies have demonstrated a role for spatial genome organization in the formation of tumorigenic abnormalities. The nonrandom localization of chromosomes and, more specifically, of genes appears to play a role in the mechanism of chromosomal translocations. Here, two-color fluorescence in situ hybridization and confocal microscopy were used to measure the interphase distance between CBFB and MYH11 in hematopoietic stem cells (HSCs), where inv(16)(p13q22) is believed to occur, leading to leukemia development. The measured distances in HSCs were compared with mesenchymal stem cells, peripheral blood lymphocytes, and fibroblasts, as spatial genome organization is determined to be cell-type specific. Results indicate that CBFB and MYH11 are significantly closer in HSCs compared with all other cell types examined. Furthermore, the CBFB-MYH11 distance is significantly reduced compared with CBFB and a control locus in HSCs, although separation between CBFB and the control is ∼70% of that between CBFB and MYH11 on metaphase chromosomes. HSCs were also treated with fragile site-inducing chemicals because both the genes contain translocation breakpoints within these regions. However, treatment with fragile site-inducing chemicals did not significantly affect the interphase distance. Consistent with previous studies, our results suggest that gene proximity may play a role in the formation of cancer-causing rearrangements, providing insight into the mechanism of chromosomal abnormalities in human tumors.