The most frequent genetic alteration in acute myeloid leukemia (AML) is the mutation of nucleophosmin 1 (NPM1). Yet, its downstream oncogenic routes are not fully understood. Here, we report the ...identification of one long noncoding RNA (lncRNA) overexpressed in NPM1-mutated AML patients (named LONA) whose intracellular localization inversely reflects that of NPM1. While NPM1 is nuclear and LONA cytoplasmic in wild-type NPM1 AML cells, LONA becomes nuclear as mutant NPM1 moves toward the cytoplasm. Gain or loss of function combined with a genome-wide RNA-seq search identified a set of LONA mRNA targets encoding proteins involved in myeloid cell differentiation (including THSB1, MAFB, and ASB2) and interaction with its microenvironment. Consistently, LONA overexpression in mutant NPM1 established cell lines and primary AML cells exerts an anti-myeloid differentiation effect, whilst it exerts an opposite pro-myeloid differentiation effect in a wild type NPM1 setting. In vivo, LONA overexpression acts as an oncogenic lncRNA reducing the survival of mice transplanted with AML cells and rendering AML tumors more resistant to AraC chemotherapy.These data indicate that mutation-dependent nuclear export of NPM1 leads to nuclear retention and consequent oncogenic functions of the overexpressed lncRNA LONA, thus uncovering a novel NPM1 mutation-dependent pathway in AML pathogenesis.
Cancer‐associated fibroblasts (CAFs) are considered the most abundant type of stromal cells in pancreatic ductal adenocarcinoma (PDAC), playing a critical role in tumour progression and ...chemoresistance; however, a druggable target on CAFs has not yet been identified. Here we report that focal adhesion kinase (FAK) activity (evaluated based on 397 tyrosine phosphorylation level) in CAFs is highly increased compared to its activity in fibroblasts from healthy pancreas. Fibroblastic FAK activity is an independent prognostic marker for disease‐free and overall survival of PDAC patients (cohort of 120 PDAC samples). Genetic inactivation of FAK within fibroblasts (FAK kinase‐dead, KD) reduces fibrosis and immunosuppressive cell number within primary tumours and dramatically decreases tumour spread. FAK pharmacologic or genetic inactivation reduces fibroblast migration/invasion, decreases extracellular matrix (ECM) expression and deposition by CAFs, modifies ECM track generation and negatively impacts M2 macrophage polarization and migration. Thus, FAK activity within CAFs appears as an independent PDAC prognostic marker and a druggable driver of tumour cell invasion.
Synopsis
Understanding how cancer‐associated fibroblasts (CAFs) promote PDAC progression is of major interest given the poor prognosis of patients. This study identifies a druggable key regulator of CAF‐induced tumour cell metastasis and a prognostic factor: the protein Focal Adhesion Kinase (FAK).
FAK activity within CAFs was an independent prognostic marker for Disease Free Survival (DFS) and Overall Survival (OS) in a cohort of 120 PDAC patients.
Activation of FAK within CAFs did not necessarily impact tumour growth, but favored tumour spread in vivo.
Fibroblastic FAK activity promoted extracellular matrix (ECM) track formation used by tumor cells to invade, and MCP‐1 secretion leading to M2 macrophage recruitment to primary tumor site.
Specific FAK inactivation within CAFs “normalized” the tumor stroma (decreased fibrosis and pro‐tumor immunity) and drastically decreased spontaneous metastasis.
PDAC patients may benefit from treatment with FAK kinase inhibitor (already clinically available) through the inhibition of the deleterious pro‐metastatic action of CAFs.
Understanding how cancer‐associated fibroblasts (CAFs) promote PDAC progression is of major interest given the poor prognosis of patients. This study identifies a druggable key regulator of CAF‐induced tumour cell metastasis and a prognostic factor: the protein Focal Adhesion Kinase (FAK).
Hypoxia has recently been shown to activate the endoplasmic reticulum kinase PERK, leading to phosphorylation of eIF2α and inhibition of mRNA translation initiation. Using a quantitative assay, we ...show that this inhibition exhibits a biphasic response mediated through two distinct pathways. The first occurs rapidly, reaching a maximum at 1–2 h and is due to phosphorylation of eIF2α. Continued hypoxic exposure activates a second, eIF2α‐independent pathway that maintains repression of translation. This phase is characterized by disruption of eIF4F and sequestration of eIF4E by its inhibitor 4E‐BP1 and transporter 4E‐T. Quantitative RT–PCR analysis of polysomal RNA indicates that the translation efficiency of individual genes varies widely during hypoxia. Furthermore, the translation efficiency of individual genes is dynamic, changing dramatically during hypoxic exposure due to the initial phosphorylation and subsequent dephosphorylation of eIF2α. Together, our data indicate that acute and prolonged hypoxia regulates mRNA translation through distinct mechanisms, each with important contributions to hypoxic gene expression.
The purpose of this review is to summarize recent experimental data describing the regulation of the phosphorylation of eIF4E, the cap-binding protein, by the MAPK-activated protein kinase Mnk1. Mnk1 ...does not interact directly with eIF4E, but uses a docking site in eIF4G, a partner of eIF4E. Consequently, control of eIF4E phosphorylation may not strictly depend on changes in Mnk1 activity. The possibility that integrity of the eIF4E/eIF4G/Mnk1 complex also impinges upon eIF4E phosphorylation is discussed.
Eukaryotic initiation factor (eIF) 4A functions
as a subunit of the initiation factor complex eIF4F, which
mediates the binding of mRNA to the ribosome. eIF4A possesses
ATPase and RNA helicase ...activities and is the prototype
for a large family of putative RNA helicases (the DEAD
box family). It is thought that the function of eIF4A during
translation initiation is to unwind the mRNA secondary
structure in the 5′ UTR to facilitate ribosome binding.
However, the evidence to support this hypothesis is rather
indirect, and it was reported that eIF4A is also required
for the translation of mRNAs possessing minimal 5′
UTR secondary structure. Were this hypothesis correct,
the requirement for eIF4A should correlate with the degree
of mRNA secondary structure. To test this hypothesis, the
effect of a dominant-negative mutant of mammalian eIF4A
on translation of mRNAs with various degrees of secondary
structure was studied in vitro. Here, we show that mRNAs
containing stable secondary structure in the 5′ untranslated
region are more susceptible to inhibition by the eIF4A
mutant. The mutant protein also strongly inhibits translation
from several picornavirus internal ribosome entry sites
(IRES), although to different extents. UV crosslinking
of eIF4F subunits and eIF4B to the mRNA cap structure is
dramatically reduced by the eIF4A mutant and RNA secondary
structure. Finally, the eIF4A mutant forms a more stable
complex with eIF4G, as compared to the wild-type eIF4A,
thus explaining the mechanism by which substoichiometric
amounts of mutant eIF4A inhibit translation.
Loss of skeletal muscle mass and force aggravates age-related sarcopenia and numerous pathologies, such as cancer and diabetes. The AKT-mTORC1 pathway plays a major role in stimulating adult muscle ...growth; however, the functional role of its downstream mediators in vivo is unknown. Here, we show that simultaneous inhibition of mTOR signaling to both S6K1 and 4E-BP1 is sufficient to reduce AKT-induced muscle growth and render it insensitive to the mTORC1-inhibitor rapamycin. Surprisingly, lack of mTOR signaling to 4E-BP1 only, or deletion of S6K1 alone, is not sufficient to reduce muscle hypertrophy or alter its sensitivity to rapamycin. However, we report that, while not required for muscle growth, S6K1 is essential for maintaining muscle structure and force production. Hypertrophy in the absence of S6K1 is characterized by compromised ribosome biogenesis and the formation of p62-positive protein aggregates. These findings identify S6K1 as a crucial player for maintaining muscle function during hypertrophy.
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•S6K1 is required for increasing adult muscle force, not muscle size•4E-BP1 and S6K1 can independently mediate rapamycin-sensitive muscle growth•Hypertrophy in the absence of S6K1 leads to the formation of protein aggregates•S6K1 is required for increases in ribosome biogenesis
Marabita et al. describe the role of the kinase S6K1 during muscle hypertrophy. They show that, surprisingly, S6K1 is not required for muscle growth but is important for stimulating ribosome biogenesis, preventing the formation of protein aggregates, and increasing muscle force.
The PI3K-AKT-mTOR pathway lies at the confluence of signaling pathways in which various components are subjected to activating genetic alterations in acute myeloid leukemia (AML), thus contributing ...to oncogenesis. Three AKT isoforms exist in humans. However, whether one isoform predominates in AML remains unknown. This study reveals that AKT3 behaves very distinctly than AKT1 or AKT2 in both normal myeloid differentiation and AML. During normal differentiation, AKT3 is preferentially expressed in hematopoietic stem cells whilst AKT1 becomes preferentially expressed as cells differentiate into granulocytes or monocytes. AKT2 expression remains unchanged. In AML, AKT3 expression varies widely among patient samples and is counterintuitively high in mature/monocytic leukemia. Furthermore, a low level of AKT3 expression is strongly correlated to genetic alterations associated with a better outcome (NPM1 mutations and RUNX1-RUNX1T1 translocation), while a high level is correlated to alterations associated to a bad outcome (RUNX1 mutations; and SRSF2, U2AF1, SF3B1, ASXL1 and BCOR mutations occurring frequently in MDS and MPN). Consistently, a high AKT3 expression level appears as a very strong predictor of poor survival. Curiously, although modestly varying among AML samples, a high AKT1 expression shows in contrast as a strong predictor of a better patient outcome. These data suggest that AKT3 and AKT1 expressions have strong, yet opposite, prognostic values.
The G protein-coupled sst2 somatostatin receptor is a critical negative regulator of cell proliferation. sstII prevents growth factor-induced cell proliferation through activation of the tyrosine ...phosphatase SHP-1 leading to induction of the cyclin-dependent kinase inhibitor p27Kip1. Here, we investigate the signaling molecules linking sst2 to p27Kip1. In Chinese hamster ovary-DG-44 cells stably expressing sst2 (CHO/sst2), the somatostatin analogue RC-160 transiently stimulates ERK2 activity and potentiates insulin-stimulated ERK2 activity. RC-160 also stimulates ERK2 activity in pancreatic acini isolated from normal mice, which endogenously express sst2, but has no effect in pancreatic acini derived from sst2 knock-out mice. RC-160-induced p27Kip1 up-regulation and inhibition of insulin-dependent cell proliferation are both prevented by pretreatment of CHO/sst2 cells with the MEK1/2 inhibitor PD98059. In addition, using dominant negative mutants, we show that sst2-mediated ERK2 stimulation is dependent on the pertussis toxin-sensitive Gi/o protein, the tyrosine kinase Src, both small G proteins Ras and Rap1, and the MEK kinase B-Raf but is independent of Raf-1. Phosphatidylinositol 3-kinase (PI3K) and both tyrosine phosphatases, SHP-1 and SHP-2, are required upstream of Ras and Rap1. Taken together, our results identify a novel mechanism whereby a Gi/o protein-coupled receptor inhibits cell proliferation by stimulating ERK signaling via a SHP-1-SHP-2-PI3K/Ras-Rap1/B-Raf/MEK pathway.
Highlights • Novel multireceptor somatostatin analogs may putatively present higher antitumor activities. • Biased agonism indicates that different somatostatin analogs cannot be considered as simple ...mimics of the native somatostatins. • Pharmacologic differences in somatostatin analogs need to be taken into account for optimal use of the somatostatin analogs in the clinic.
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