Project description:Inactivating mutations in the zinc finger gene PHF6 are seen in approximately 40% of adult T-cell acute lymphoblastic leukemias (T-ALLs) and 3% of adult acute myeloid leukemias (AMLs). The absence of PHF6 mutations in B-cell lineage malignancies has led to the hypothesis that PHF6 may act as a lineage-specific tumor suppressor gene. Here, we demonstrate that PHF6 plays a critical role in regulating B-cell identity in the context of B-cell precursor acute lymphoblastic leukemia (preB-ALL). Transplantation of Phf6 knockout preB-ALL cells (hereafter referred to as Phf6KO cells) into immunocompetent syngeneic recipients resulted in the development of a fully penetrant lymphoma-like disease. Strikingly, the resulting lymphomas showed robust up-regulation of the canonical T-cell marker CD4, suggesting that Phf6KO cells adopt a T-cell program in the context of leukemogenesis. RNA sequencing analysis revealed numerous differentially expressed (DE) genes in Phf6WT and Phf6KO cells, including a significant down-regulation of genes and gene sets involved in pathways important for B-cell development. Chromatin immunoprecipitation followed by high-throughput sequencing analysis revealed that PHF6 co-localizes with H3K27ac signals close to the transcription start sites (TSSs) and enhancer regions of a significant proportion of DE genes. Notably, regions flanking the TSS of DE genes showed significant enrichment for binding sites of several well-described master regulators of B-cell development, including PU.1, EGR-1, EBF-1, NF-kB, TCF3 and TCF12. We found that PHF6 and TCF12 physically interact in preB-ALL cells, suggesting that these factors act synergistically in the establishment and maintenance of B-cell identity. In addition, we found that a human PHF6 mutant T-ALL cell line has an incompletely rearranged IGH locus, strongly suggesting that T-ALL can have a B-cell origin. These findings reveal an essential role for PHF6 in the establishment and maintenance of B-cell identity in preB-ALL by directly activating genes that are crucial for B-cell lineage commitment and maintenance. Collectively, these results indicate that loss of function of PHF6 in preB-ALL leads to an unstable cellular state in which cells acquire alternate developmental programs (such as the T-lineage program) to survive, potentially explaining the apparent absence of PHF6 mutations in human B cell-lineage malignancies.
Project description:Inactivating mutations in the zinc finger gene PHF6 are seen in approximately 40% of adult T-cell acute lymphoblastic leukemias (T-ALLs) and 3% of adult acute myeloid leukemias (AMLs). The absence of PHF6 mutations in B-cell lineage malignancies has led to the hypothesis that PHF6 may act as a lineage-specific tumor suppressor gene. Here, we demonstrate that PHF6 plays a critical role in regulating B-cell identity in the context of B-cell precursor acute lymphoblastic leukemia (preB-ALL). Transplantation of Phf6 knockout preB-ALL cells (hereafter referred to as Phf6KO cells) into immunocompetent syngeneic recipients resulted in the development of a fully penetrant lymphoma-like disease. Strikingly, the resulting lymphomas showed robust up-regulation of the canonical T-cell marker CD4, suggesting that Phf6KO cells adopt a T-cell program in the context of leukemogenesis. RNA sequencing analysis revealed numerous differentially expressed (DE) genes in Phf6WT and Phf6KO cells, including a significant down-regulation of genes and gene sets involved in pathways important for B-cell development. Chromatin immunoprecipitation followed by high-throughput sequencing analysis revealed that PHF6 co-localizes with H3K27ac signals close to the transcription start sites (TSSs) and enhancer regions of a significant proportion of DE genes. Notably, regions flanking the TSS of DE genes showed significant enrichment for binding sites of several well-described master regulators of B-cell development, including PU.1, EGR-1, EBF-1, NF-kB, TCF3 and TCF12. We found that PHF6 and TCF12 physically interact in preB-ALL cells, suggesting that these factors act synergistically in the establishment and maintenance of B-cell identity. In addition, we found that a human PHF6 mutant T-ALL cell line has an incompletely rearranged IGH locus, strongly suggesting that T-ALL can have a B-cell origin. These findings reveal an essential role for PHF6 in the establishment and maintenance of B-cell identity in preB-ALL by directly activating genes that are crucial for B-cell lineage commitment and maintenance. Collectively, these results indicate that loss of function of PHF6 in preB-ALL leads to an unstable cellular state in which cells acquire alternate developmental programs (such as the T-lineage program) to survive, potentially explaining the apparent absence of PHF6 mutations in human B cell-lineage malignancies.
Project description:Inactivating mutations in the zinc finger gene PHF6 are seen in approximately 40% of adult T-cell acute lymphoblastic leukemias (T-ALLs) and 3% of adult acute myeloid leukemias (AMLs). The absence of PHF6 mutations in B-cell lineage malignancies has led to the hypothesis that PHF6 may act as a lineage-specific tumor suppressor gene. Here, we demonstrate that PHF6 plays a critical role in regulating B-cell identity in the context of B-cell precursor acute lymphoblastic leukemia (preB-ALL). Transplantation of Phf6 knockout preB-ALL cells (hereafter referred to as Phf6KO cells) into immunocompetent syngeneic recipients resulted in the development of a fully penetrant lymphoma-like disease. Strikingly, the resulting lymphomas showed robust up-regulation of the canonical T-cell marker CD4, suggesting that Phf6KO cells adopt a T-cell program in the context of leukemogenesis. RNA sequencing analysis revealed numerous differentially expressed (DE) genes in Phf6WT and Phf6KO cells, including a significant down-regulation of genes and gene sets involved in pathways important for B-cell development. Chromatin immunoprecipitation followed by high-throughput sequencing analysis revealed that PHF6 co-localizes with H3K27ac signals close to the transcription start sites (TSSs) and enhancer regions of a significant proportion of DE genes. Notably, regions flanking the TSS of DE genes showed significant enrichment for binding sites of several well-described master regulators of B-cell development, including PU.1, EGR-1, EBF-1, NF-kB, TCF3 and TCF12. We found that PHF6 and TCF12 physically interact in preB-ALL cells, suggesting that these factors act synergistically in the establishment and maintenance of B-cell identity. In addition, we found that a human PHF6 mutant T-ALL cell line has an incompletely rearranged IGH locus, strongly suggesting that T-ALL can have a B-cell origin. These findings reveal an essential role for PHF6 in the establishment and maintenance of B-cell identity in preB-ALL by directly activating genes that are crucial for B-cell lineage commitment and maintenance. Collectively, these results indicate that loss of function of PHF6 in preB-ALL leads to an unstable cellular state in which cells acquire alternate developmental programs (such as the T-lineage program) to survive, potentially explaining the apparent absence of PHF6 mutations in human B cell-lineage malignancies.
Project description:Tumor suppressor genes on the X chromosome may skew the gender distribution of specific types of cancer. T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy with an increased incidence in males. In this study, we report the identification of inactivating mutations and deletions in the X-linked plant homeodomain finger 6 (PHF6) gene in 16% of pediatric and 38% of adult primary T-ALL samples. Notably, PHF6 mutations are almost exclusively found in T-ALL samples from male subjects. Mutational loss of PHF6 is importantly associated with leukemias driven by aberrant expression of the homeobox transcription factor oncogenes TLX1 and TLX3. Overall, these results identify PHF6 as a new X-linked tumor suppressor in T-ALL and point to a strong genetic interaction between PHF6 loss and aberrant expression of TLX transcription factors in the pathogenesis of this disease.