Assembly of mTORC3 Involves Binding of ETV7 to Two Separate Sequences in the mTOR Kinase Domain.

mTOR plays a crucial role in cell growth by controlling ribosome biogenesis, metabolism, autophagy, mRNA translation, and cytoskeleton organization. It is a serine/threonine kinase that is part of two distinct extensively described protein complexes, mTORC1 and mTORC2. We have identified a rapamycin-resistant mTOR complex, called mTORC3, which is different from the canonical mTORC1 and mTORC2 complexes in that it does not contain the Raptor, Rictor, or mLST8 mTORC1/2 components.

Mitochondrial proteostasis mediated by CRL5 and Alix maintains skeletal muscle function.

High energy-demanding tissues, such as skeletal muscle, require mitochondrial proteostasis to function properly. Two quality-control mechanisms, the ubiquitin proteasome system (UPS) and the release of mitochondria-derived vesicles, safeguard mitochondrial proteostasis. However, whether these processes interact is unknown.

Haploinsufficiency of the lysosomal sialidase NEU1 results in a model of pleomorphic rhabdomyosarcoma in mice.

Rhabdomyosarcoma, the most common pediatric sarcoma, has no effective treatment for the pleomorphic subtype. Still, what triggers transformation into this aggressive phenotype remains poorly understood. Here we used Ptch1/ETV7 mice with enhanced incidence of rhabdomyosarcoma to generate a model of pleomorphic rhabdomyosarcoma driven by haploinsufficiency of the lysosomal sialidase neuraminidase 1.

Targeting KDM4 for treating PAX3-FOXO1-driven alveolar rhabdomyosarcoma.

Chimeric transcription factors drive lineage-specific oncogenesis but are notoriously difficult to target. Alveolar rhabdomyosarcoma (RMS) is an aggressive childhood soft tissue sarcoma transformed by the pathognomonic Paired Box 3-Forkhead Box O1 (PAX3-FOXO1) fusion protein, which governs a core regulatory circuitry transcription factor network. Here, we show that the histone lysine demethylase 4B (KDM4B) is a therapeutic vulnerability for PAX3-FOXO1 RMS.

Lysosomes and Cancer Progression: A Malignant Liaison.

During primary tumorigenesis isolated cancer cells may undergo genetic or epigenetic changes that render them responsive to additional intrinsic or extrinsic cues, so that they enter a transitional state and eventually acquire an aggressive, metastatic phenotype. Among these changes is the alteration of the cell metabolic/catabolic machinery that creates the most permissive conditions for invasion, dissemination, and survival. The lysosomal system has emerged as a crucial player in this malignant transformation, making this system a potential therapeutic target in cancer.

MYC competes with MiT/TFE in regulating lysosomal biogenesis and autophagy through an epigenetic rheostat.

Coordinated regulation of the lysosomal and autophagic systems ensures basal catabolism and normal cell physiology, and failure of either system causes disease. Here we describe an epigenetic rheostat orchestrated by c-MYC and histone deacetylases that inhibits lysosomal and autophagic biogenesis by concomitantly repressing the expression of the transcription factors MiT/TFE and FOXH1, and that of lysosomal and autophagy genes. Inhibition of histone deacetylases abates c-MYC binding to the promoters of lysosomal and autophagy genes, granting promoter occupancy to the MiT/TFE members, TFEB and TFE3, and/or the autophagy regulator FOXH1.

Phosphorylation of TSC2 by PKC-δ reveals a novel signaling pathway that couples protein synthesis to mTORC1 activity.

Downstream of insulin-like growth factor receptor, the TSC1/2/ TCB1D7 (tuberous sclerosis complex) and mTOR (mechanistic target of rapamycin) pathways are implicated in many human diseases, including cancer and diabetes. Targeting this pathway is currently an important approach for palliating or eradicating cancer. Downstream of mTOR, translational machinery targeting holds great promise for anticancer drug development.

Establishment of a transgenic mouse to model ETV7 expressing human tumors.

The ETS transcription factor ETV7 has been characterized as a hematopoietic oncoprotein, which requires cooperating mutations for its leukemogenic activity. Although the ETV7 gene is highly conserved among vertebrates, part of the rodents, including Mus musculus, deleted the Etv7 gene locus. Many human hematopoietic malignancies upregulate ETV7 expression but contrary to ETV7's role in oncogenesis, its physiological role in normal tissues is unknown.

ETV7 is an essential component of a rapamycin-insensitive mTOR complex in cancer.

The mechanistic target of rapamycin (mTOR) serine/threonine kinase, a critical regulator of cell proliferation, is frequently deregulated in human cancer. Although rapamycin inhibits the two canonical mTOR complexes, mTORC1 and mTORC2, it often shows minimal benefit as an anticancer drug. This is caused by rapamycin resistance of many different tumors, and we show that a third mTOR complex, mTORC3, contributes to this resistance.

Modeling of the human alveolar rhabdomyosarcoma Pax3-Foxo1 chromosome translocation in mouse myoblasts using CRISPR-Cas9 nuclease.

Many recurrent chromosome translocations in cancer result in the generation of fusion genes that are directly implicated in the tumorigenic process. Precise modeling of the effects of cancer fusion genes in mice has been inaccurate, as constructs of fusion genes often completely or partially lack the correct regulatory sequences. The reciprocal t(2;13)(q36.

Zebrafish ETV7 regulates red blood cell development through the cholesterol synthesis pathway.

ETV7 is a human oncoprotein that cooperates with Eμ-MYC to promote pre-B-cell leukemia in mice. It is normally expressed in the bone marrow and fetal liver and is upregulated in primary leukemia, suggesting that it is involved in proper hematopoiesis and leukemogenesis. ETV7 has been deleted in most rodents, but is conserved in all other vertebrates, including the zebrafish, Danio rerio.

Distinct and overlapping sarcoma subtypes initiated from muscle stem and progenitor cells.

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children, whereas undifferentiated pleomorphic sarcoma (UPS) is one of the most common soft tissue sarcomas diagnosed in adults. To investigate the myogenic cell(s) of origin of these sarcomas, we used Pax7-CreER and MyoD-CreER mice to transform Pax7(+) and MyoD(+) myogenic progenitors by expressing oncogenic Kras(G12D) and deleting Trp53 in vivo. Pax7-CreER mice developed RMS and UPS, whereas MyoD-CreER mice developed UPS.

PAX3-FOXO1 induces up-regulation of Noxa sensitizing alveolar rhabdomyosarcoma cells to apoptosis.

Alveolar rhabdomyosarcoma (ARMS) has a much poorer prognosis than the more common embryonal subtype. Most ARMS tumors characteristically possess a specific genomic translocation between the genes of PAX3/7 and FOXO1 (FKHR), which forms fusion proteins possessing the DNA binding domains of PAX3/7 and the more transcriptionally potent transactivation domain of FOXO1. We have shown that the proapoptotic BH3-only family member Noxa is upregulated by the PAX3-FOXO1 fusion transcription factor in a p53-independent manner.

Mapping of MN1 sequences necessary for myeloid transformation.

The MN1 oncogene is deregulated in human acute myeloid leukemia and its overexpression induces proliferation and represses myeloid differentiation of primitive human and mouse hematopoietic cells, leading to myeloid leukemia in mouse models. To delineate the sequences within MN1 necessary for MN1-induced leukemia, we tested the transforming capacity of in-frame deletion mutants, using retroviral transduction of mouse bone marrow. We found that integrity of the regions between amino acids 12 to 458 and 1119 to 1273 are required for MN1's in vivo transforming activity, generating myeloid leukemia with some mutants also producing T-cell lympho-leukemia and megakaryocytic leukemia.

Alveolar rhabdomyosarcoma - The molecular drivers of PAX3/7-FOXO1-induced tumorigenesis.

Rhabdomyosarcoma is a soft tissue sarcoma arising from cells of a mesenchymal or skeletal muscle lineage. Alveolar rhabdomyosarcoma (ARMS) is more aggressive than the more common embryonal (ERMS) subtype. ARMS is more prone to metastasis and carries a poorer prognosis.

The leukemia-associated fusion protein MN1-TEL blocks TEL-specific recognition sequences.

The leukemia-associated fusion protein MN1-TEL combines the transcription-activating domains of MN1 with the DNA-binding domain of the transcriptional repressor TEL. Quantitative photobleaching experiments revealed that ∼20% of GFP-tagged MN1 and TEL is transiently immobilised, likely due to indirect or direct DNA binding, since transcription inhibition abolished immobilisation. Interestingly, ∼50% of the MN1-TEL fusion protein was immobile with much longer binding times than unfused MN1 and TEL.

PAX3-FOXO1 induces cannabinoid receptor 1 to enhance cell invasion and metastasis.

Alveolar rhabdomyosarcoma (ARMS) is a muscle-derived childhood tumor characterized by production of oncogenic PAX3/7-FOXO1 chimeric transcription factors. While downstream targets of the PAX3-FOXO1 oncoprotein in ARMS have been defined, the functional relevance of these targets is unclear. Here, we show that upregulation of the cannabinoid receptor 1 (Cnr1/Cb1) by PAX3-FOXO1 in mouse primary myoblasts and ARMS cell lines, contributes to PAX3-FOXO1 phenotypes, both in vivo and in vitro.

PAX3-FOXO1 and FGFR4 in alveolar rhabdomyosarcoma.

We and others have identified FGFR4 as a direct transcriptional target of the alveolar rhabdomyosarcoma (ARMS) specific fusion protein, PAX3-FOXO1. We hypothesized fibroblast growth factor receptor 4 (FGFR4) may act as an effector of PAX3-FOXO1, contributing to PAX3-FOXO1 tumorigenic phenotypes. However, we demonstrate that enhanced expression of FGFR4 does not contribute to inhibited differentiation, enhanced proliferation, or transformation downstream of PAX3-FOXO1 in primary mouse myoblasts.

IRIZIO: a novel gene cooperating with PAX3-FOXO1 in alveolar rhabdomyosarcoma (ARMS).

Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma in children with an annual incidence of five new cases per million. Alveolar rhabdomyosarcoma (ARMS) is characterized by the t(2;13) or t(1;13) chromosomal translocations, which generate the PAX3-FOXO1 or PAX7-FOXO1 fusion genes, respectively. The oncogenic activity of PAX3-FOXO1 has been demonstrated in vitro and in vivo, yet expression of the fusion protein alone in primary myoblasts or a mouse model is insufficient for tumorigenic transformation.

Reintroduction of CEBPA in MN1-overexpressing hematopoietic cells prevents their hyperproliferation and restores myeloid differentiation.

Forced expression of MN1 in primitive mouse hematopoietic cells causes acute myeloid leukemia and impairs all-trans retinoic acid-induced granulocytic differentiation. Here, we studied the effects of MN1 on myeloid differentiation and proliferation using primary human CD34(+) hematopoietic cells, lineage-depleted mouse bone marrow cells, and bipotential (granulocytic/monocytic) human acute myeloid leukemia cell lines. We show that exogenous MN1 stimulated the growth of CD34(+) cells, which was accompanied by enhanced survival and increased cell cycle traverse in cultures supporting progenitor cell growth.

Overexpression of the cellular DEK protein promotes epithelial transformation in vitro and in vivo.

High levels of expression of the human DEK gene have been correlated with numerous human malignancies. Intracellular DEK functions have been described in vitro and include DNA supercoiling, DNA replication, RNA splicing, and transcription. We have shown that DEK also suppresses cellular senescence, apoptosis, and differentiation, thus promoting cell growth and survival in monolayer and organotypic epithelial raft models.

MN1 affects expression of genes involved in hematopoiesis and can enhance as well as inhibit RAR/RXR-induced gene expression.

The oncoprotein meningioma 1 (MN1) is overexpressed in several subtypes of acute myeloid leukemia (AML) and overexpression was associated with a poor response to chemotherapy. MN1 is a cofactor of retinoic acid receptor/retinoic x receptor (RAR/RXR)-mediated transcription and this study identified genes in the promonocytic cell line U937 that were regulated by MN1. We found that MN1 can both stimulate and inhibit transcription.

Overexpression of N-Myc rapidly causes acute myeloid leukemia in mice.

N-MYC encodes a basic helix-loop-helix/leucine zipper (bHLH/LZ) transcription factor that is frequently overexpressed in human neuroblastoma. N-MYC overexpression has also been reported in human acute myeloid leukemias (AML), which we show here is a frequent event. Myeloid cells in N-Myc-overexpressing mouse bone marrow hyperproliferate but those in c-MYC-overexpressing bone marrow do not.

MN1, a novel player in human AML.

The transcriptional coactivator MN1 has been identified as a gene overexpressed in certain types of human acute myeloid leukemia. Upregulation is invariantly associated with inv(16) AML but is also found in other AML subtypes. Overexpression of this gene is also associated with a worse prognosis and a shorter survival in AML patients with a normal karyotype.