Project description:Recently, screens for mediators of resistance to FLT3 and ABL kinase inhibitors in leukemia resulted in the discovery of LZTR1 as an adaptor of a Cullin-3 RING E3 ubiquitin ligase complex responsible for degradation of RAS GTPases. In parallel, dysregulated LZTR1 expression via aberrant splicing and mutations have been identified in clonal hematopoietic conditions. Here we identify that loss of LZTR1, or leukemia-associated mutants in the LZTR1 substrate and RAS GTPase RIT1 which escape degradation, drive hematopoietic stem cell expansion (HSC) and leukemia in vivo. LZTR1 null cells rely on multiple RAS GTPases for transformation. Consequently, RAS targeting bioPROTACs or reduction of GTP-loaded RAS overcomes LZTR1 loss-mediated resistance to FLT3 inhibitors. These data thereby reveal proteolysis of non-canonical RAS proteins as novel regulators of HSC function, define the function and spectrum of RIT1 and LZTR1 mutations in leukemia, and identify means to overcome drug resistance due to LZTR1 downregulation.
Project description:Recently, screens for mediators of resistance to FLT3 and ABL kinase inhibitors in leukemia resulted in the discovery of LZTR1 as an adaptor of a Cullin-3 RING E3 ubiquitin ligase complex responsible for degradation of RAS GTPases. In parallel, dysregulated LZTR1 expression via aberrant splicing and mutations have been identified in clonal hematopoietic conditions. Here we identify that loss of LZTR1, or leukemia-associated mutants in the LZTR1 substrate and RAS GTPase RIT1 which escape degradation, drive hematopoietic stem cell expansion (HSC) and leukemia in vivo. LZTR1 null cells rely on multiple RAS GTPases for transformation. Consequently, RAS targeting bioPROTACs or reduction of GTP-loaded RAS overcomes LZTR1 loss-mediated resistance to FLT3 inhibitors. These data thereby reveal proteolysis of non-canonical RAS proteins as novel regulators of HSC function, define the function and spectrum of RIT1 and LZTR1 mutations in leukemia, and identify means to overcome drug resistance due to LZTR1 downregulation.
Project description:Though limited proteolysis of the histone H3 N-terminal tail (H3NT) is frequently observed during mammalian differentiation, however the specific genomic sites targeted for H3NT proteolysis and their functional significance of H3NT cleavage remain unknown.We used genome wide Chip-seq (ChIPac-Seq) approaches to an established cell model of osteoclast differentiation. We discovered that H3NT proteolysis is selectively targeted near transcription start sites of a small group of genes and that most of these H3NT-cleaved genes are epigenetically regulated during osteoclastogenesis.We also discovered that the principal H3NT protease of osteoclastogenesis is matrix metalloproteinase 9 (MMP-9).Abrogation of H3NT proteolysis impaired osteoclastogenic gene activation concomitant with defective osteoclast differentiation. In summary our results support the necessity of MMP-9-dependent H3NT proteolysis in the epigenetic reprogramming of gene pathways required for proficient osteoclastogenesis.
Project description:The differential expression of microRNAs in Ras transformed epithelial cells of human and rat origin was investigated. Here we describe the group of miRNAs differentially expressed in two Ras transformed cell lines and defined it as a miRNA Ras signatures. We show that expression of these miRNAs are also affected in different primary tumors with high frequency of Ras mutation. We demonstate that introduction of different miRNAs lost during Ras transformation have big influence on cellular phenotype and mRNA expression. Importance of Ras pathway dependent transcription factors for miRNA regulation was shown as well. The complexity of miRNA – signal transduction pathways interactions and importance of miRNA regulation in Ras dependent malignant tumor formation is discussed.
Project description:The tumor suppressor protein p27Kip1 plays a pivotal role in the control of cell growth and metastasis formation.Several studies pointed to different roles for p27Kip1 in the control of Ras induced transformation, although no explanation has been provided to elucidate these differences. We recently demonstrated that p27kip1 regulates H-Ras activity via its interaction with stathmin.Here, using in vitro and in vivo models, we show that p27kip1 is an important regulator of Ras induced transformation. In H-RasV12 transformed cells, p27kip1 suppressed cell proliferation and tumor growth via two distinct mechanisms: 1) inhibition of CDK activity and 2) impairment of MT-destabilizing activity of stathmin. Conversely, in K-Ras4BV12 transformed cells, p27kip1 acted mainly in a CDK-dependent but stathmin-independent manner.Using human cancer-derived cell lines and primary breast and sarcoma samples, we confirmed in human models what we observed in mice.Overall, we highlight a pathway, conserved from mouse to human, important in the regulation of H-Ras oncogenic activity that could have therapeutic and diagnostic implication in patients that may benefit from anti-H-Ras therapies.
Project description:The differential expression of microRNAs in Ras transformed epithelial cells of human and rat origin was investigated. Here we describe the group of miRNAs differentially expressed in two Ras transformed cell lines and defined it as a miRNA Ras signatures. We show that expression of these miRNAs are also affected in different primary tumors with high frequency of Ras mutation. We demonstate that introduction of different miRNAs lost during Ras transformation have big influence on cellular phenotype and mRNA expression. Importance of Ras pathway dependent transcription factors for miRNA regulation was shown as well. The complexity of miRNA – signal transduction pathways interactions and importance of miRNA regulation in Ras dependent malignant tumor formation is discussed.
Project description:The oncogenic proteins expressed in human cancer cells are exceedingly difficult targets for drug discovery due to intrinsic properties of the Ras GTPase switch. As a result, recent efforts have largely focused on inhibiting Ras-regulated kinase effector cascades, particularly the Raf/MEK/ERK and PI3 kinase/Akt/mTOR pathways. We constructed murine stem cell leukemia virus (MSCV) vectors encoding oncogenic K-RasD12 with additional “second site” amino acid substitutions that that impair PI3 kinase/Akt or Raf/MEK/ERK activation and performed bone marrow transduction/transplantation experiments in mice. In spite of attenuated signaling properties, defective K-Ras oncoproteins induced aggressive clonal T lineage acute lymphoblastic leukemia (T-ALL). These leukemias exhibited a high frequency of somatic Notch1 mutations, which is also true of human T-ALL. Multiple independent T-ALLs restored full oncogenic Ras activity by acquiring “third site” mutations within the viral KrasD12 transgenes. Other leukemias with undetectable PTEN and elevated phosphoryated Akt levels showed a similar gene expression profile to human early T progenitor (ETP) T-ALL. Expressing oncoproteins that are defective for specific functions is a general strategy for assessing requirements for tumor maintenance and uncovering potential mechanisms of drug resistance in vivo. In addition, our observation that defective Kras oncogenes regain potent cancer initiating activity strongly supports simultaneously targeting distinct components of Ras signaling networks in the substantial fraction of cancers with RAS mutations. WT Balb/c mice were lethally irradiated and transplanted with WT Balb/c bone marrow cells transduced with MSCV-IRES-Kras mutant-GFP vectors. Mice developed T-cell lymphoproliferative disease.