SATB acts as a master regulator
SATB2 acts as a master regulator by binding to genes which regulate embryonic development, cell differentiation, pluripotency, and cell survival (Ordonez, 2014; Rosenfeld et al., 2009; Zhao et al., 2014). We have discovered the SATB2 JSH-23 in the promoters of c-Myc, Nanog, Kl4, Bcl-2 and XIAP genes. These SATB2 target genes directly regulate pluripotency, cell survival, cell growth and differentiation in progenitor and transformed cells. Our Chip data confirmed that SATB2 can directly bind to these genes in breast cancer stem cells. The ability of SATB2 to induce transformation of mammary epithelial cells suggests that it is capable of regulating de-differentiation that results into formation of progenitor-like cells. Interestingly, these cells were capable of forming colonies and mammospheres. In an appropriate microenvironment, these cells will be able to form pathologically similar breast cancer tissues. Further studies with SATB2 transgenic or knockout mice will be needed to confirm the role of SATB2 in breast cancer initiation, progression and metastasis.
Authors\' contributions WY and YM=performed the experiments, analyzed the data, and wrote the manuscript. SS and RKS=designed the study and contributed reagents. All the authors approved the manuscript.
Disclosure of potential conflicts of interest
Resource details Acute Megakaryoblastic Leukemia (AMKL) is a type of acute myeloid leukemia (AML) characterized by the accumulation of immature megakaryoblasts in bone marrow and thrombocytopenia (Athale et al., 2001; Hama et al., 2008; Paredes-Aguilera et al., 2003). Pediatric AMKL not associated to Down Syndrome (non-DS AMKL) has a bad prognosis, with a mortality rate of >50% and an average survival of 2years (Gruber and Downing, 2015). Approximately 15% of non-DS AMKL pediatric patients carry the t(1;22) chromosomal translocation that generates the oncogenic fusion protein RBM15-MKL1 (Gruber and Downing, 2015). As this is a rare disease, there is only a limited access to patient samples and a reduced amount of available in vitro models. Therefore, it is essential to establish new human models that will provide enough biological material to perform functional and molecular studies. The early onset of pediatric leukemias, the high rate of disease concordance in monozygotic twins, and the presence of leukemia-associated chromosomal translocations in cells from bloodspots collected at birth indicate that the initiating lesions are acquired in utero (Greaves, 2005; Wiemels et al., 2002). Thus, hPSCs represent an ideal model for studying the mechanisms of infant leukemia development and progression in a relevant cellular context (Dvash et al., 2006; Greaves, 2006). We have generated two hPSC cell lines constitutively expressing the fusion oncogene RBM15-MKL1. These cell lines represent new non-DS AMKL in vitro disease models. They will help us understand the impact of the RBM15-MKL1 oncogene in the early stages of human embryonic hematopoietic development, and how it contributes to the acquisition of a leukemic phenotype. We transduced the iPSC cell line PBMC2-iPS4F8 (Montes et al., manuscript in preparation) and the hESC cell line H9 (Thomson et al., 1998) with lentiviruses expressing either a control, empty pRRL-Neo vector (Neo cell lines), or a pRRL-HA-RBM15-MKL1-Neo vector (RM cell lines) (Fig. 1A). After selection with Neomycin for 10days we obtained resistant colonies that were expanded, leading to the establishment of the following four cell lines, which retained the typical morphology of undifferentiated hPSCs: H9 Neo, H9 RM, PBMC2-iPS4F8 Neo, and PBMC2-iPS4F8 RM (Fig. 1B). We confirmed by quantitative PCR that the RM cell lines express the oncogene RBM15-MKL1, and that the PCR product was specific (Fig. 1C). The expression of RBM15-MKL1 in the RM cell lines resulted in an increased expression of several genes previously described as being targets of RBM15-MKL1, including genes of the Notch pathway (Mercher et al., 2009; Niu et al., 2009) (Fig. 1D). We also detected an increase in the expression of the endogenous MKL1 and both variants of RBM15 genes (Fig. 1D). We confirmed the identity of the transgenic cell lines by Short Tandem Repeat (STR) profiling (Fig. 1E). Of note, in the H9 cell lines (Neo and RM) the marker TPOX has changed from 10, 11 to only 11 (Fig. 1E and F), while in the PBMC2-iPS4F8 cell lines (Neo and RM) the marker D13S317 shows the appearance of a new incipient peak at position 14 (Fig. 1E and G).