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Identification and analysis of PU.1 cell death pathways to improve leukemia therapy

English title Identification and analysis of PU.1 cell death pathways to improve leukemia therapy
Applicant Tschan Mario P.
Number 173219
Funding scheme Project funding (Div. I-III)
Research institution Institut für Pathologie Medizinische Fakultät Universität Bern
Institution of higher education University of Berne - BE
Main discipline Experimental Cancer Research
Start/End 01.05.2017 - 30.04.2021
Approved amount 693'641.00
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All Disciplines (4)

Discipline
Experimental Cancer Research
Cellular Biology, Cytology
Molecular Biology
Pathophysiology

Keywords (6)

Apoptosis; Alternative splicing; Chemoresistance; PU.1; Acute Myeloid Leukemia; TRAIL

Lay Summary (German)

Lead
Die Behandlung von gewissen Untertypen der Akute Myeloischen Leukämie (AML) zeigt erfreuliche Fortschritte. Da die AML aber eine äusserst heterogene Krankheit darstellt, sind weitere Untersuchungen, die zur Aufklärung der dieser Krankheit zugrunde liegenden molekularen Mechanismen dienen, für die Entwicklung neuer Behandlungsansätze zusätzlicher AML Untertypen äusserst wichtig.
Lay summary

Generell, ist die AML durch eine Ansammlung von nicht ausdifferenzierten Blutzellen gekennzeichnet. Die Ursachen für diesen anormalen Differenzierungsstopp kann verschiedene Ursachen haben, z.B. die Inaktivierung von Proteinen, sogenannten Transkriptionsfaktoren, welche die Transkription von wichtigen Genen für die Differenzierung steuern. Ein solcher Transkriptionsfaktor ist PU.1. Frühere Studien zeigten, dass die Expression von PU.1 in AML signifikant reduziert ist und PU.1 wurde als AML Tumorsuppressor postuliert.

Unsere aktuellen Ergebnisse zeigten eine neue, eher unerwartete Rolle für PU.1 in der Initierung von Zelltod in AML Zellen. Wir konnten zeigen, dass PU.1 die Expression und Funktion von Genen, welche das Überleben von AML Zellen fördern, behindern kann. Dies würde die Funktion von PU.1 über die Rolle in der Differenzierung hinaus erweitern, und macht die Reaktivierung dieses Transkriptionsfaktors ein interessantes therapeutisches Ziel. In einem ersten Schritt, untersuchen wir den PU.1 Mechanismus im Zell-Tod unter Verwendung der neuesten Molekularbiologie- und Zellkultur-Techniken. In einem zweiten Schritt, werden wir versuchen die Expression von PU.1 in AML Zellen wieder herzustellen, und damit hoffentlich die Sensitivität gegenüber gängigen zelltoxischen Krebstherapien erhöhen.

Unser Grundlagenforschungs-Projekt zielt also darauf ab, die neuen Funktionen von PU.1 im AML Zell-Tod besser zu verstehen, damit wir mittels Re-aktivierung von PU.1 in Kombination mit anderen AML Therapien die Wirksamkeit der Behandlung erhöhen können. 

Direct link to Lay Summary Last update: 19.07.2017

Responsible applicant and co-applicants

Employees

Associated projects

Number Title Start Funding scheme
143739 PU.1-regulated apoptosis and autophagy pathways in neutrophil differentiation of normal and leukemic myeloid precursor cells 01.01.2013 Project funding (Div. I-III)
166578 Analyzing and modulating the epigenetic landscape of CDX2 as well as studying its function in colorectal cancer pathology 01.06.2016 Project funding (Div. I-III)
143739 PU.1-regulated apoptosis and autophagy pathways in neutrophil differentiation of normal and leukemic myeloid precursor cells 01.01.2013 Project funding (Div. I-III)
183501 Installing a Hyperion CyTOF mass cytometry platform for high-dimensional single cell analysis at the University of Bern 01.10.2019 R'EQUIP

Abstract

The ETS-transcription factor PU.1 is needed throughout hematopoietic differentiation particularly by orchestrating terminal differentiation of macrophages, neutrophils, B-cells and Th9 cells. The role of PU.1 in myeloid differentiation and its regulation have been thoroughly investigated and many genes directly involved in myeloid development and function are transcriptional targets of PU.1. Importantly, low but not absent PU.1 expression can lead to the transformation of myeloid progenitor cells to acute myeloid leukemia (AML). Thus, PU.1 is regarded as a tumor suppressor in AML, a disease that is characterized by an accumulation of immature blast cells with increased cell survival. Much less information is available on PU.1’s function in cell death or cell cycle regulation. Comprehensive functional studies analyzing the role of PU.1 during cell death responses of AML cells to cancer therapies are missing. Our preliminary data describe a new tumor suppressor function for PU.1 by supporting TNF-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis in AML cells. Our data indicate that PU.1 represses the NF-?B survival pathway, and thus the induction of anti-apoptotic genes such as cFLIP, Bcl-2 or Mcl-1. Furthermore, blocking PU.1 expression causes a shift in cFLIP expression towards the anti-apoptotic splice variant cFLIPshort. Altogether, these results indicate a new facet of PU.1's tumor suppressor function during anti-leukemic therapy and low PU.1 levels may contribute to resistance towards TRAIL treatment. Moreover, inhibiting PU.1 also attenuates AML cell toxicity caused by anthracycline-based therapies. In my opinion, further studies to decipher mechanisms how PU.1 affects cell death and how PU.1 protein stability is regulated during cancer therapy warrants further investigations. Findings from this project hold potential for improved therapeutic strategies in mainly AML treatment and a better understanding of how PU.1 keeps neoplastic transformations in check. I propose to investigate in more detail how PU.1 regulates responses to cytotoxic particularly death receptor mediated therapies I suggest to address the following objectives: I. PU.1 mechanisms in response to cytotoxic therapy. I propose, (a) to validate our 2D cell culture findings in 3D in vitro and in vivo, (b) to further characterize PU.1’s cell death function in regard of TRAIL receptor regulation, (c) to validate possible apoptotic functions of PU.1 in additional hematopoietic neoplasms, (d) to investigate PU.1’s role in epigenetic regulation of cell death-associated genes. II. I propose, (a) to initially investigate if blocking major cellular degradation processes (e.g. caspases, necroptosis, proteasome, autophagy) affect PU.1 protein expression, and (b) to characterize the PU.1 protein interactome during cytotoxic treatment and to inhibit/activate newly identified proteins involved in PU.1 protein stability for novel therapeutic options in cytotoxic therapies.III. PU.1 and alternative splicing of cFLIP. I propose, (a) to analyze the function of cFLIP in resistance towards TRAIL treatment and chemotherapy, (b) to test if PU.1 associates with the cFLIP promoter region to promote specific use of splice sites, and (c) to investigate if PU.1 transcriptionally regulates posttranslational modifiers of cFLIP.The proposed studies will help to unravel novel functions of PU.1 in cell death responses to cancer therapies and may further elucidate its role in suppressing leukemia by targeting anti-apoptotic proteins. Identifying factors that regulate PU.1 protein stability may provide novel targets to be used in combination with current cytotoxic therapies.
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