Establishment of induced pluripotent stem cells from normal B cells and inducing AID expression in their differentiation into hematopoietic progenitor cells

ΔNp63α transcriptionally represses p53 target genes involved in the radiation-induced DNA damage response : ΔNp63α may cause genomic instability in epithelial stem cells

BACKGROUND

The DNA damage response (DDR) is a mechanism that protects cells against radiation-induced oxidative DNA damage by causing cell cycle arrest and apoptosis. TP63 is a member of the tumour suppressor TP53 gene family, and ΔNp63α, a TP63 splicing variant, is constitutively expressed in the stem cell-containing basal layer of stratified epithelial tissues, including the mammary gland, where it plays a critical role in stemness and tissue development. ΔNp63α has been reported to transcriptionally inhibit the tumour suppression protein p53. This p53-repressive activity may cause genomic instability in epithelial stem cells exposed to radiation. In this study, we analysed the inhibitory effect of ΔNp63α on radiation-induced DDR.

METHODS

To elucidate the role of the p53-repressive effect of ΔNp63α in radiation response, we performed a p63-siRNA knockdown experiment using human mammary epithelial cells (HMECs) expressing ΔNp63α and then performed ectopic and entopic expression experiments using human induced pluripotent stem cells (hiPSCs). After irradiation, the expression of DDR-related genes and proteins in ΔNp63α-expressing and control cells was analysed by RT-qPCR, Western blotting, and flow cytometry.

RESULTS

The mRNA/protein expression levels of BAX and p21 were significantly increased in p63-siRNA-treated HMECs (sip63) after X-ray irradiation (4 Gy, 0.7 Gy/min) but not in scramble-siRNA treated HMECs (scr). Transcriptomic analysis showed decreased RNA expression of cell cycle-related genes and increased expression of programmed cell death-related genes in sip63 cells compared to scr cells. Furthermore, flow cytometric analysis revealed an increase in apoptotic cells and a decrease in 5-ethynyl-2´-deoxyuridine uptake in sip63 cells compared to scr cells. On the other hand, both the ectopic and entopic expression of ΔNp63α in apoptosis-sensitive hiPSCs reduced the expression levels of BAX after irradiation and significantly decreased the number of apoptotic cells induced by radiation.

CONCLUSION

Taken together, these results indicate that ΔNp63α represses p53-related radiation-induced DDR, thereby potentially causing genomic instability in epithelial stem cells.

Chromosomal translocation t(11;14) and p53 deletion induced by the CRISPR/Cas9 system in normal B cell-derived iPS cells

Multiple myeloma (MM) cells are derived from mature B cells based on immunoglobulin heavy chain (IgH) gene analysis. The onset of MM is often caused by a reciprocal chromosomal translocation (cTr) between chr 14 with IgH and chr 11 with CCND1. We propose that mature B cells gain potential to transform by reprograming, and then chromosomal aberrations cause the development of abnormal B cells as a myeloma-initiating cell during B cell redifferentiation. To study myeloma-initiating cells, we have already established normal B cell-derived induced pluripotent stem cells (BiPSCs). Here we established two BiPSCs with reciprocal cTr t(11;14) using the CRISPR/Cas9 system; the cleavage site were located in the IgH Eμ region of either the VDJ rearranged allele or non-rearranged allele of IgH and the 5'-upsteam region of the CCND1 (two types of BiPSC13 with t(11;14) and MIB2-6 with t(11;14)). Furthermore, p53 was deleted using the CRISPR/Cas9 system in BiPSC13 with t(11;14). These BiPSCs differentiated into hematopoietic progenitor cells (HPCs). However, unlike cord blood, those HPCs did not differentiated into B lymphocytes by co-culture with BM stromal cell. Therefore, further ingenuity is required to differentiate those BiPSCs-derived HPCs into B lymphocytes.

Induction of t(11;14) IgH enhancer/promoter-cyclin D1 gene translocation using CRISPR/Cas9

Chromosomal translocation is a key process in the oncogenic transformation of somatic cells. Previously, artificial induction of chromosomal translocation was performed using homologous recombination-mediated loxP labeling of target regions followed by Cre-mediated recombination. Recent progress in genome editing techniques has facilitated the easier induction of artificial translocation by cutting two targeted genome sequences from different chromosomes. The present study established a system to induce t(11;14)(q13;q32), which is observed primarily in multiple myeloma (MM) and involves the repositioning of the cyclin D1 (CCND1) gene downstream of the immunoglobulin heavy chain (IgH) constant region enhancers by translocation. The placing of tandem gRNAs designed to cut both the IgH Eµ and CCND1 15-kb upstream regions in lentiCRISPRv2 enabled the induction of chromosomal translocation in 293T cells, with confirmation by translocation-specific PCR and fluorescence in situ hybridization probing with IgH and CCND1. At the translocation junctions, small deletions and the addition of DNA sequences (indels) were observed in several clones. Cloned cells with t(11;14) exhibited slower growth and lower CCND1 mRNA expression compared to the parent cells, presenting the opposite phenomena induced by t(11;14) in MM cells, indicating that the silent IgH gene juxtaposed to CCND1 may negatively affect CCND1 gene expression and cell proliferation in the non-B lymphocyte lineage. Therefore, the present study achieved the induction of silent promoter/enhancer translocation in t(11;14)(q13;q32) as a preparatory experiment to study the role of IgH constant region enhancer-driven CCND1 overexpression in oncogenic transformation processes in B lymphocytes.