A carregar...
Projeto de investigação
Sem título
Financiador
Autores
Publicações
Dissecting the cellular and molecular mechanisms of IL-7-mediated leukemia T-cell survival proliferation and cell growth
Publication . Ribeiro, Daniel; Barata, João Taborda,
T-cell acute lymphoblastic leukemia (T-ALL) constitutes an aggressive subset of ALL, the most frequent childhood malignancy. Although risk-adjusted chemotherapeutic regimens are currently extremely effective, they frequently associate with significant long-term side effects. Moreover, cases that do not respond to therapy or that relapse have dismal prognosis. Thus, better therapies focused on efficacy and specificity against T-ALL cells are necessary. Understanding the biology and molecular pathogenesis of T-cell leukemogenesis is critical to carry out this goal. Interleukin-7 (IL-7) and its receptor (IL-7R; heterodimer constituted by IL-7Rα/IL7R and γc/IL2RG subunits) are essential for normal T-cell development and there is considerable evidence that IL 7-mediated signaling may promote leukemogenesis. Mice overexpressing IL-7 develop B- and T-cell lymphomas and increased expression of IL-7Rα, present in AKR/J mice, promotes development of T-cell tumors. Furthermore, IL-7 promotes T-ALL expansion in vivo and leukemia cell survival and proliferation in vitro. We assessed whether activating IL-7R mutations could occur in T-ALL. We found that 9% of T-ALL patients harbor somatic gain-of function IL7R mutations. The majority introduced an unpaired cysteine in exon 6 and promoted IL-7Rα homodimerization, which led to constitutive signaling that relied exclusively on Jak1. We found that IL7R mutations promote cell transformation and tumor formation. Importantly, mutant IL-7R signaling (and consequent increase in viability and proliferation) was targetable with Jak/STAT5 pathway inhibitors (Chapter 2). Previously, we have shown that IL-7 promotes leukemia cell survival and proliferation in vitro by activating PI3K/Akt/mTOR signaling pathway. The observation that IL-7-driven murine lymphomagenesis requires STAT5 and the fact that IL-7R-mutated T-ALL are sensitive to Jak/STAT5 pathway inhibitors, led us to investigate the role of this pathway in T-ALL. Here, we showed that inhibition of STAT5 in T-ALL completely abrogates IL-7-mediated T-ALL cell viability, growth and proliferation. Importantly, we demonstrated that survival mediated by IL-7 via STAT5 was independent from expression of Bcl-2 family members. Next generation sequencing analysis (NGS) revealed that PIM1 kinase is a direct STAT5 target in the context of IL-7 signaling and that PIM1 is required for IL-7/Jak/STAT5-mediated functional effects. In addition, we provide evidence that IL-7 downregulates the expression of BCL6 and promotes transcription of an alternate transcript (Chapter 3). Autophagy may mitigate stress, such as that induced by oncogene-driven proliferation or chemotherapy, in cancer cells. However, when persistent, its protective role may shift to what is called autophagic cell death. Since IL-7 promotes activation of mTOR, a master negative regulator of autophagy, we decided to explore whether IL-7 may also regulate T-ALL cell autophagy. We demonstrated that IL-7 modulates autophagy in T-ALL cells in a complex manner that involves triggering both pro- (MEK/Erk) and anti- (PI3K/Akt/mTOR) autophagic signaling pathways. Our data suggest that depending on the microenvironmental cues, IL-7 uses a 'flexible strategy' to shift the signaling pathway required for survival. In a nutrient-rich microenvironment (low autophagy) IL-7 inhibits autophagy and survival relies on PI3K/Akt/mTOR, while in nutrient-poor conditions (high autophagy) IL-7 promotes autophagy and survival relies on MEK/Erk pathway activation (Chapter 4). IL-7 maintains cell size and metabolic activity in normal T-cells. Also, IL-7 promotes expression of Glut1 and hexokinase II (HK2), both involved in glycolysis. In T-ALL, we previously showed that IL-7 mediated cell growth, promoted glucose use and Glut1 expression. Using NGS data obtained in Chapter 2, we extended the knowledge on IL-7-mediated T ALL cell metabolism. We provide significant evidence that IL-7 is broadly involved in upregulation of glycolysis in T-ALL. Gene expression analysis showed that IL-7 promotes very early expression of several glycolytic genes, including those involved in key stages of glycolysis regulation (Chapter 5). Taken together, the studies presented in this work significantly expand our understanding of the role of the IL 7/IL-7R signaling axis in T-ALL. The discovery of oncogenic IL7R mutations may have important therapeutic implications in T-ALL. In addition, we provide clear evidence that targeting Jak/STAT5/PIM1 and MEK/Erk pathways in IL-7 signaling constitute new promising therapeutic targets. We also unravel new roles for IL-7 in important physiological processes, such as autophagy and glycolysis, which may help devise new therapeutic strategies in T-cell leukemia.
Unidades organizacionais
Descrição
Palavras-chave
Contribuidores
Financiadores
Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
SFRH
Número da atribuição
SFRH/BD/69781/2010