RESUMO
Infant acute leukemias are aggressive and characterized by rapid onset after birth. The majority harbor translocations involving the MLL gene with AF9 as one of its most common fusion partners. MLL and AF9 loci contain breakpoint cluster regions (bcrs) with sequences hypothesized to be targets of topoisomerase II inhibitors that promote translocation formation. Overlap of MLL bcr sequences associated with both infant acute leukemia and therapy-related leukemia following exposure to the topoisomerase II inhibitor etoposide led to the hypothesis that exposure during pregnancy to biochemically similar compounds may promote infant acute leukemia. We established a reporter system to systematically quantitate and stratify the potential for such compounds to promote chromosomal translocations between the MLL and AF9 bcrs analogous to those in infant leukemia. We show bioflavonoids genistein and quercetin most biochemically similar to etoposide have a strong association with MLL-AF9 bcr translocations, while kaempferol, fisetin, flavone, and myricetin have a weak but consistent association, and other compounds have a minimal association in both embryonic stem (ES) and hematopoietic stem cell (HSC) populations. The frequency of translocations induced by bioflavonoids at later stages of myelopoiesis is significantly reduced by more than one log. The MLL and AF9 bcrs are sensitive to these agents and recombinogenic independent of their native context suggesting bcr sequences themselves are drivers of illegitimate DNA repair reactions and translocations, not generation of functional oncogenic fusions. This system provides for rapid systematic screening of relative risk, dose dependence, and combinatorial impact of multitudes of dietary and environmental exposures on MLL-AF9 translocations. Environ. Mol. Mutagen. 60: 154-167, 2019. © 2018 Wiley Periodicals, Inc.
Assuntos
Flavonoides/toxicidade , Leucemia/genética , Proteína de Leucina Linfoide-Mieloide/genética , Proteínas de Fusão Oncogênica/genética , Translocação Genética/efeitos dos fármacos , Quebra Cromossômica/efeitos dos fármacos , Pontos de Quebra do Cromossomo/efeitos dos fármacos , Cromossomos/efeitos dos fármacos , Cromossomos/genética , Exposição Ambiental/efeitos adversos , Feminino , Humanos , Lactente , Leucemia/induzido quimicamente , Leucemia/patologia , Gravidez , Medição de RiscoRESUMO
The presence of histones acts as a barrier to protein access; thus chromatin remodeling must occur for essential processes such as transcription and replication. In conjunction with histone modifications, DNA methylation plays critical roles in gene silencing through chromatin remodeling. Chromatin remodeling is also interconnected with the DNA damage response, maintenance of stem cell properties, and cell differentiation programs. Chromatin modifications have increasingly been shown to produce long-lasting alterations in chromatin structure and transcription. Recent studies have shown environmental exposures in utero have the potential to alter normal developmental signaling networks, physiologic responses, and disease susceptibility later in life during a process known as developmental reprogramming. In this review we discuss the long-term impact of exposure to environmental compounds, the chromatin modifications that they induce, and the differentiation and developmental programs of multiple stem and progenitor cell types altered by exposure. The main focus is to highlight agents present in the human lifestyle that have the potential to promote epigenetic changes that impact developmental programs of specific cell types, may promote tumorigenesis through altering epigenetic marks, and may be transgenerational, for example, those able to be transmitted through multiple cell divisions.
Assuntos
Montagem e Desmontagem da Cromatina/genética , Dano ao DNA/genética , Dieta/efeitos adversos , Exposição Ambiental/efeitos adversos , Células-Tronco/patologia , Carcinogênese/efeitos dos fármacos , Carcinogênese/genética , Montagem e Desmontagem da Cromatina/efeitos dos fármacos , Dano ao DNA/efeitos dos fármacos , Metilação de DNA/efeitos dos fármacos , Metilação de DNA/genética , Epigênese Genética/efeitos dos fármacos , Epigênese Genética/genética , Regulação da Expressão Gênica/efeitos dos fármacos , Regulação da Expressão Gênica/genética , Humanos , Células-Tronco/efeitos dos fármacos , Células-Tronco/metabolismo , Fatores de TempoRESUMO
Yeast prions, based on self-seeded highly ordered fibrous aggregates (amyloids), serve as a model for human amyloid diseases. Propagation of yeast prions depends on the balance between chaperones of the Hsp100 and Hsp70 families. The yeast prion [PSI(+)] can be eliminated by an excess of the chaperone Hsp104. This effect is reversed by an excess of the chaperone Hsp70-Ssa. Here we show that the actions of Hsp104 and Ssa on [PSI(+)] are modulated by the small glutamine-rich tetratricopeptide cochaperone Sgt2. Sgt2 is conserved from yeast to humans, has previously been implicated in the guided entry of tail-anchored proteins (GET) trafficking pathway, and is known to interact with Hsps, cytosolic Get proteins, and tail-anchored proteins. We demonstrate that Sgt2 increases the ability of excess Ssa to counteract [PSI(+)] curing by excess Hsp104. Deletion of SGT2 also restores trafficking of a tail-anchored protein in cells with a disrupted GET pathway. One region of Sgt2 interacts both with the prion domain of Sup35 and with tail-anchored proteins. Sgt2 levels are increased in response to the presence of a prion when major Hsps are not induced. Our data implicate Sgt2 as an amyloid "sensor" and a regulator of chaperone targeting to different types of aggregation-prone proteins.
