Suppression of MBD2 alternative splicing promotes breast cancer metastasis by activating FZD1 under hypoxia
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ABSTRACT: Metastasis is responsible for the majority of breast cancer (BrCa) deaths; however, the underlying mechanisms remain largely elusive. Here, we report that suppression of MBD2 alternative splicing under hypoxia, which favors the production of MBD2a, facilitates BrCa metastasis. Specifically, we found that MBD2a promotes, whereas its less-known short form MBD2c suppresses metastasis. We elucidate that HIF-1 activation under hypoxia facilitates MBD2a production via repression of SRSF2-mediated alternative splicing and, as a result, the elevated MBD2a outcompetes MBD2c for binding to the promoter CpG islands to activate the expression of FZD1, thereby promoting EMT and metastasis. Strikingly, clinical data reveals significantly correlated expression pattern of MBD2a and MBD2c with the invasiveness of malignancy, indicating the opposing roles for MBD2 splicing variants in regulating human BrCa metastasis. Thus, our findings establish a novel link between MBD2 switching and tumor metastasis, and provide promising therapeutic strategy and predictive biomarkers for hypoxia-driven BrCa metastasis.
Project description:Using global gene expression and proteomic analyses, we identified a molecular signature in human embryonic and induced pluripotent stem cells that suggested a central regulatory role for RNA splicing in self-renewal. Through genetic and biochemical approaches, we established reciprocal functional links between the master regulatory factor OCT4 and SFRS2, a member of the serine/arginine-rich family of splicing factors. SFRS2 regulates expression of two isoforms of the methyl-CpG-binding protein MBD2 that play opposing roles in human ESC and during the reprogramming of fibroblasts. Both the MBD2a isoform expressed in fibroblasts and the MBD2c isoform found in pluripotent cells bind OCT4 and NANOG promoters in human ESC, but only MBD2a interacts with NuRD chromatin remodeling factors. Members of the miR-301 and miR-302 families provide additional regulation by targeting SFRS2 and the somatic specific MBD2a isoform. These data are consistent with a model in which OCT4, SFRS2, and MBD2 participate in a positive feedback loop to regulate proteome diversity in support of self-renewal in pluripotent cells. We isolated RNA from human iPS cells, different human fibroblasts and human embryonic stem cells for hybridization to the Affymetrix gene expression microarrays.
Project description:Alternative RNA splicing (AS) regulates proteome diversity, including isoform-specific expression of several pluripotency genes. Here, we integrated global gene expression and proteomic analyses and identified a molecular signature suggesting a central role for AS in maintaining human pluripotent stem cell (hPSC) self-renewal. We demonstrate the splicing factor SFRS2 is an OCT4 target gene required for pluripotency. SFRS2 regulates AS of the methyl-CpG-binding protein MBD2, whose isoforms play opposing roles in maintenance of, and reprogramming to, pluripotency. While both MDB2a and MBD2c are enriched at the OCT4 and NANOG promoters, MBD2a preferentially interacts with repressive NuRD chromatin remodeling factors and promotes hPSC differentiation, whereas overexpression of MBD2c enhances reprogramming of fibroblasts to pluripotency. The miR-301 and miR-302 families provide additional regulation by targeting SFRS2 and MDB2a. These data suggest that OCT4, SFRS2, and MBD2 participate in a positive feedback loop, regulating proteome diversity complexity in support of hPSC self-renewal and reprogramming. We isolated RNA from human fibroblasts and human embryonic stem cells for hybridization to the Affymetrix gene expression microarrays.
Project description:Using global gene expression and proteomic analyses, we identified a molecular signature in human embryonic and induced pluripotent stem cells that suggested a central regulatory role for RNA splicing in self-renewal. Through genetic and biochemical approaches, we established reciprocal functional links between the master regulatory factor OCT4 and SFRS2, a member of the serine/arginine-rich family of splicing factors. SFRS2 regulates expression of two isoforms of the methyl-CpG-binding protein MBD2 that play opposing roles in human ESC and during the reprogramming of fibroblasts. Both the MBD2a isoform expressed in fibroblasts and the MBD2c isoform found in pluripotent cells bind OCT4 and NANOG promoters in human ESC, but only MBD2a interacts with NuRD chromatin remodeling factors. Members of the miR-301 and miR-302 families provide additional regulation by targeting SFRS2 and the somatic specific MBD2a isoform. These data are consistent with a model in which OCT4, SFRS2, and MBD2 participate in a positive feedback loop to regulate proteome diversity in support of self-renewal in pluripotent cells.
Project description:Alternative RNA splicing (AS) regulates proteome diversity, including isoform-specific expression of several pluripotency genes. Here, we integrated global gene expression and proteomic analyses and identified a molecular signature suggesting a central role for AS in maintaining human pluripotent stem cell (hPSC) self-renewal. We demonstrate the splicing factor SFRS2 is an OCT4 target gene required for pluripotency. SFRS2 regulates AS of the methyl-CpG-binding protein MBD2, whose isoforms play opposing roles in maintenance of, and reprogramming to, pluripotency. While both MDB2a and MBD2c are enriched at the OCT4 and NANOG promoters, MBD2a preferentially interacts with repressive NuRD chromatin remodeling factors and promotes hPSC differentiation, whereas overexpression of MBD2c enhances reprogramming of fibroblasts to pluripotency. The miR-301 and miR-302 families provide additional regulation by targeting SFRS2 and MDB2a. These data suggest that OCT4, SFRS2, and MBD2 participate in a positive feedback loop, regulating proteome diversity complexity in support of hPSC self-renewal and reprogramming.
Project description:During human development, there is a switch in the erythroid compartment at birth that results in silencing of expression of fetal hemoglobin (HbF). Reversal of this silencing has been shown to be effective in overcoming the pathophysiologic defect in sickle cell anemia. Among the many transcription factors and epigenetic effectors that are known to mediate HbF silencing, two of the most potent are BCL11A and MBD2-NuRD. In this report we present direct evidence that MBD2- NuRD occupies the γ-globin gene promoter in adult erythroid cells and positions a nucleosome there that results in a closed chromatin conformation that prevents binding of the transcriptional activator, NF-Y. We show that the specific isoform, MBD2a, is required for the formation and stable occupancy of this repressor complex that includes BCL11A, MBD2a-NuRD and the arginine methyltransferase, PRMT5. The methyl cytosine binding preference and the arginine rich (GR) domain of MBD2a are required for high affinity binding to methylated γ-globin gene proximal promoter DNA sequences. Mutation of the methyl cytosine binding domain of MBD2 results in a variable but consistent loss of γ-globin gene silencing, in support of the importance of promoter methylation. The GR domain of MBD2a is also required for recruitment of PRMT5, which in turn results in placement of the repressive chromatin mark H3K8me2s at the promoter. These findings 2 support a unified model that integrates the respective roles of BCL11A, MBD2a-NuRD, PRMT5 and DNA methylation in HbF silencing.
Project description:To obtain a comprehensive and quantitative view on MBD2 vs MBD3-NuRD complex stoichiometry, we performed biotin co-immunoprecipitations in Mbd3 KO ES cells expressing either biotin-tagged MBD2a or MBD3a and identified known NuRD complex members using label-free mass spectrometry (Supplementary Fig. 8b-c). We then calculated the intensity-based absolute quantification (iBAQ) values of the most predominant and statistically significant MBD-interacting proteins in both cell lines, which can be used to estimate the relative abundance. While we observe very similar complex composition between MBD2a-NuRD and MBD3a-NuRD, peptides shared between SALL1-4 proteins show a preferred interaction with the MBD2a-NuRD complex.
Project description:The Nucleosome Remodeling and Deacetylation (NuRD) complex is a crucial regulator of cellular differentiation. Two members of the Methyl-CpG-binding domain (MBD) protein family, MBD2 and MBD3, are known to be integral, but mutually exclusive subunits of the NuRD complex. Several MBD2 and MBD3 isoforms are present in mammalian cells, resulting in distinct MBD-NuRD complexes. Whether these different complexes serve distinct functional activities during differentiation is not fully explored. Based on the essential role of MBD3 in lineage commitment, we systematically investigated a diverse set of MBD2 and MBD3 variants for their potential to rescue the differentiation block observed for mouse embryonic stem cells (ESCs) lacking MBD3. While MBD3 is indeed crucial for ESC differentiation to neuronal cells, it functions independently of its MBD domain. We further identify that MBD2 isoforms can replace MBD3 during lineage commitment, however with different potential. Full-length MBD2a only partially rescues the differentiation block, while MBD2b, an isoform lacking an N-terminal GR-rich repeat, fully rescues the Mbd3 KO phenotype. In case of MBD2a, we further show that removing the methylated DNA binding capacity or the GR-rich repeat enables full redundancy to MBD3, highlighting the synergistic requirements for these domains in diversifying NuRD complex function.
Project description:The heterogeneous collection of NuRD complexes can be grouped into the MBD2 or MBD3 containing complexes MBD2-NuRD and MBD3-NuRD. MBD2 is known to bind to methylated CpG sequences in vitro in contrast to MBD3. Although functional differences have been described, a direct comparison of MBD2 and MBD3 in respect to genome-wide binding and function has been lacking. Here we show when depleting cells for MBD2, the MBD2 bound genes increase their activity, whereas MBD2 plus MBD3 bound genes reduce their activity. Most strikingly, MBD3 is enriched at active promoters, whereas MBD2 is bound at methylated promoters and enriched at exon sequences of active genes. This suggests a functional connection between MBD2 binding to chromatin and splicing.
Project description:Mitochondria contain a 16kb-dsDNA genome encoding 13 proteins essential for respiration, whereas its regulatory mechanism and potential role in cancer development remain elusive. Although Methyl-CpG-binding protein (MBD) proteins are essential for nuclear transcription, their role in mitochondrial DNA (mtDNA) transcription is unknown. Here, we report that the MBD2c splicing variant translocates into mitochondria to mediate mtDNA transcription and increase mitochondrial respiration in triple negative breast cancer (TNBC) cells. Specifically, MBD2c binds D-loop regions in mtDNA to recruit SIRT3, which in turn deacetylates TFAM, a primary mitochondrial transcription factor, and activates its function. TFAM activation subsequently enhances transcription of the whole mitochondrial genome. Furthermore, MBD2c overexpression recovered the decreased mtDNA-encoded RNA and protein levels induced by the DNA synthesis inhibitor, cisplatin (CDDP), in vitro and in vivo, preserving mitochondrial gene expression and respiration, consequently enhancing TNBC cells drug resistance and proliferation. These data collectively demonstrate that MBD2c positively regulates mtDNA transcription, thus connecting epigenetic regulation by deacetylation with cancer cell metabolism, suggesting druggable targets to overcome resistance.