Our research focuses on the signals that control stem cell self-renewal and how these signals are hijacked in cancer. Using a series of genetic models, we have studied how classic developmental ...signaling pathways play key roles in hematopoietic stem cell growth and regeneration and are dysregulated during leukemia development. Through this work we have identified Hedgehog and Wnt signaling, and more recently the cell fate determinant Musashi, as critical players in driving progression of hematologic malignancies and as targets for therapy. To search for new regulators of myeloid leukemia, we have carried out a focused screen of surface molecules that may enable leukemia cells to receive supportive cues from the microenvironment. This screen identified key new adhesion signals that are critical to leukemia growth, drug resistance and dissemination. Using high resolution in vivo imaging we have mapped how these mediate the interactions that leukemia cells make within their microenvironment. To complement this focused screen, we have also carried out a genome wide CRISPR screen to more generally define the biological determinants of myeloid leukemia establishment and propagation. This screen identified a large number of new genes and programs critically required for leukemia, including those essential for chromatin remodeling and spliceosomal assembly. Among these, RNA binding proteins (RBPs) in general, and the chromatin binding sub-family of RBPs in particular, emerged as key new dependencies of myeloid leukemia. The talk will focus in part on these new regulators.
No relevant conflicts of interest to declare.
Although we have come a long way in our understanding of the signals that drive cancer growth, and how these signals can be targeted, effective control of this disease remains a key scientific and ...medical challenge. The therapy resistance and relapse that are commonly seen are driven in large part by the inherent heterogeneity within cancers that allows drugs to effectively eliminate some, but not all, malignant cells. Here, we focus on the fundamental drivers of this heterogeneity by examining emerging evidence that shows that these traits are often controlled by the disruption of normal cell fate and aberrant adoption of stem cell signals. We discuss how undifferentiated cells are preferentially primed for transformation and often serve as the cell of origin for cancers. We also consider evidence showing that activation of stem cell programmes in cancers can lead to progression, therapy resistance and metastatic growth and that targeting these attributes may enable better control over a difficult disease.
While standard therapies can lead to an initial remission of aggressive cancers, they are often only a transient solution. The resistance and relapse that follows is driven by tumor heterogeneity and ...therapy-resistant populations that can reinitiate growth and promote disease progression. There is thus a significant need to understand the cell types and signaling pathways that not only contribute to cancer initiation, but also those that confer resistance and drive recurrence. Here, we discuss work showing that stem cells and progenitors may preferentially serve as a cell of origin for cancers, and that cancer stem cells can be key in driving the continued growth and functional heterogeneity of established cancers. We also describe emerging evidence for the role of developmental signals in cancer initiation, propagation, and therapy resistance and discuss how targeting these pathways may be of therapeutic value.
Mammalian tissues are fuelled by circulating nutrients, including glucose, amino acids, and various intermediary metabolites. Under aerobic conditions, glucose is generally assumed to be burned fully ...by tissues via the tricarboxylic acid cycle (TCA cycle) to carbon dioxide. Alternatively, glucose can be catabolized anaerobically via glycolysis to lactate, which is itself also a potential nutrient for tissues and tumours. The quantitative relevance of circulating lactate or other metabolic intermediates as fuels remains unclear. Here we systematically examine the fluxes of circulating metabolites in mice, and find that lactate can be a primary source of carbon for the TCA cycle and thus of energy. Intravenous infusions of
C-labelled nutrients reveal that, on a molar basis, the circulatory turnover flux of lactate is the highest of all metabolites and exceeds that of glucose by 1.1-fold in fed mice and 2.5-fold in fasting mice; lactate is made primarily from glucose but also from other sources. In both fed and fasted mice,
C-lactate extensively labels TCA cycle intermediates in all tissues. Quantitative analysis reveals that during the fasted state, the contribution of glucose to tissue TCA metabolism is primarily indirect (via circulating lactate) in all tissues except the brain. In genetically engineered lung and pancreatic cancer tumours in fasted mice, the contribution of circulating lactate to TCA cycle intermediates exceeds that of glucose, with glutamine making a larger contribution than lactate in pancreatic cancer. Thus, glycolysis and the TCA cycle are uncoupled at the level of lactate, which is a primary circulating TCA substrate in most tissues and tumours.
Immunoglobulin (Ig) class switch recombination (CSR) is the process occurring in mature B cells that diversifies the effector component of antibody responses. CSR is initiated by the activity of the ...B cell-specific enzyme activation-induced cytidine deaminase (AID), which leads to the formation of programmed DNA double-strand breaks (DSBs) at the Ig heavy chain (Igh) locus. Mature B cells use a multilayered and complex regulatory framework to ensure that AID-induced DNA breaks are channeled into productive repair reactions leading to CSR, and to avoid aberrant repair events causing lymphomagenic chromosomal translocations. Here, we review the DNA repair pathways acting on AID-induced DSBs and their functional interplay, with a particular focus on the latest developments in their molecular composition and mechanistic regulation.
Mature B cells rely on a multilayered regulatory framework to ensure that S region DSBs are preferentially channeled into the NHEJ pathway.The structure of AID-induced breaks influences both the DSB end-processing mode and end-joining pathway choice.Both the SSA factor RAD52 and the A-EJ protein HMCES contribute strand pairing activities during repair of S region DSBs.Repair of AID-initiated breaks is influenced by Igh locus-specific organizational features that ensure productive end-joining events leading to CSR. 53BP1 contributes both structural and resection modulatory roles to the regulation of CSR repair outcomes.Shieldin and CST complexes are 53BP1 and Rif1 downstream effectors, and actively counteract the processing of S region DSBs into ssDNA by combining inhibition of DNA end resection and limited fill-in synthesis of resected tracks.
Insulin Receptor Substrate (IRS), an intracellular molecule devoid of an intrinsic kinase activity, is activated upon binding to IR which thereby works as a scaffold, organizing all signaling ...complexes and initiating the signaling process downstream. The level of IRS proteins and their stability in the cell is mostly maintained through the phosphorylation status of their tyrosine and serine residues. IRS is positively regulated by phosphorylation of its Tyr residues whereas a Ser residue phosphorylation attenuates it, although there exist some exceptions as well. Other post-translational modifications like O-linked glycosylation, N-linked glycosylation and acetylation also play a prominent role in IRS regulation. Since the discovery of the Warburg effect, people have been curious to find out all possible signaling networks and molecules that could lead to cancer and no doubt, the insulin signaling pathway is identified as one such pathway, which is highly deregulated in cancers. Eminent studies reveal that IRS is a pertinent regulator of cancer and is highly overexpressed in the five most commonly occurring cancers namely- Prostate, Ovarian, Breast, Colon and Lung cancers. IRS1 and IRS2 family members are actively involved in the progression, invasion and metastasis of these cancers. Recently, less studied IRS4 has also emerged as a contributor in ovarian, breast, colorectal and lung cancer, but no such studies related to IRS4 are found in Prostate cancer. The involvement of other IRS family members in cancer is still undiscovered and so paves the way for further exploration. This review is a time-lapse study of IRSs in the context of cancer done over the past two decades and it highlights all the major discoveries made till date, in these cancers from the perspective of IRS.
•IRS is the central molecule responsible for relaying the extracellular stimuli induced effects via its varied signaling network.•Activation and deactivation of IRS is regulated by the phosphorylation at its Tyrosine and Serine residues respectively.•IRS has a multifaceted involvement in progression and development of cancers.
Our research focuses on the signals that control stem cell self-renewal and how these signals are hijacked in cancer. Using genetic models, we have shown that classic developmental signaling pathways ...such as Wnt and Hedgehog play key roles in stem cell growth and regeneration and are dysregulated during leukemia development. In addition, we have used real-time imaging strategies to show that stem cells have the capacity to undergo both symmetric and asymmetric division, and that shifts in the balance between these modes of division are controlled by the microenvironment and subverted by oncogenes. This work led to the discovery that regulators of asymmetric division, such as the cell fate determinant Musashi, can promote aggressive leukemias and may serve as critical targets for diagnostics and therapy in hematologic malignancies. Most recently, we have developed a high resolution in vivo imaging system that has allowed us to begin to map the behavior and interactions of stem cells with the microenvironment within living animals and to define how these change during cancer formation.
No relevant conflicts of interest to declare.
Mammalian 53BP1 and replication timing regulatory factor 1 (RIF1) protect DNA double-strand breaks (DSBs) against nucleolytic degradation through the recruitment of the REV7-SHLD1-SHLD2-SHLD3 ...(shieldin) and CTC1–STN1–TEN1 (CST) complexes.Mouse models deficient in downstream effectors of DSB protection have enabled the comparative assessment of defects in V(D)J recombination and class switch recombination (CSR).Regulation of DSB resection is crucial for CSR but dispensable for V(D)J recombination.The DSB protection function of mammalian 53BP1 does not explain the CSR defect severity associated with its deficiency.V(D)J recombination and CSR rely on the dynamic reconfiguration of Tcr/Ig loci that is contributed by cohesin-mediated loop extrusion.We propose that mammalian 53BP1 mediates pre- and post-break functions related to Tcr/Ig dynamics and DSB end-tethering, respectively, during the two recombination reactions.
The dissection of the key molecular activities contributed by 53BP1 to antibody gene diversification exemplifies the importance of considering the repair of V(D)J and class switch recombination DNA double-strand breaks in their architectural genomic contexts. The investigation of the close interplay between Tcr/Ig loci dynamics and the repair of these programmed breaks can provide a deeper understanding of the molecular bases of humoral immune responses.
The DNA double-strand break (DSB) repair factor 53BP1 has long been implicated in V(D)J and class switch recombination (CSR) of mammalian lymphocyte receptors. However, the dissection of the underlying molecular activities is hampered by a paucity of studies V(D)J and plurality of phenotypes (CSR) associated with 53BP1 deficiency. Here, we revisit the currently accepted roles of 53BP1 in antibody diversification in view of the recent identification of its downstream effectors in DSB protection and latest advances in genome architecture. We propose that, in addition to end protection, 53BP1-mediated end-tethering stabilization is essential for CSR. Furthermore, we support a pre-DSB role during V(D)J recombination. Our perspective underscores the importance of evaluating repair of DSBs in relation to their dynamic architectural contexts.
The DNA double-strand break (DSB) repair factor 53BP1 has long been implicated in V(D)J and class switch recombination (CSR) of mammalian lymphocyte receptors. However, the dissection of the underlying molecular activities is hampered by a paucity of studies V(D)J and plurality of phenotypes (CSR) associated with 53BP1 deficiency. Here, we revisit the currently accepted roles of 53BP1 in antibody diversification in view of the recent identification of its downstream effectors in DSB protection and latest advances in genome architecture. We propose that, in addition to end protection, 53BP1-mediated end-tethering stabilization is essential for CSR. Furthermore, we support a pre-DSB role during V(D)J recombination. Our perspective underscores the importance of evaluating repair of DSBs in relation to their dynamic architectural contexts.
Lineage commitment and differentiation is driven by the concerted action of master transcriptional regulators at their target chromatin sites. Multiple efforts have characterized the key ...transcription factors (TFs) that determine the various hematopoietic lineages. However, the temporal interactions between individual TFs and their chromatin targets during differentiation and how these interactions dictate lineage commitment remains poorly understood. Here we perform dense, daily, temporal profiling of chromatin accessibility (DNase I-seq) and gene expression changes (total RNA-seq) along ex vivo human erythropoiesis to comprehensively define developmentally regulated DNase I hypersensitive sites (DHSs) and transcripts. We link both distal DHSs to their target gene promoters and individual TFs to their target DHSs, revealing that the regulatory landscape is organized in distinct sequential regulatory modules that regulate lineage restriction and maturation. Finally, direct comparison of transcriptional dynamics (bulk and single-cell) and lineage potential between erythropoiesis and megakaryopoiesis uncovers differential fate commitment dynamics between the two lineages as they exit the stem and progenitor stage. Collectively, these data provide insights into the temporally regulated synergy of the cis- and the trans-regulatory components underlying hematopoietic lineage commitment and differentiation.
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