Brf1 loss and not overexpression disrupts tissues homeostasis in the intestine, liver and pancreas

RNA polymerase III (Pol-III) transcribes tRNAs and other small RNAs essential for protein synthesis and cell growth. Pol-III is deregulated during carcinogenesis; however, its role in vivo has not been studied. To address this issue, we manipulated levels of Brf1, a Pol-III transcription factor that is essential for recruitment of Pol-III holoenzyme at tRNA genes in vivo. Knockout of Brf1 led to embryonic lethality at blastocyst stage. In contrast, heterozygous Brf1 mice were viable, fertile and of a normal size. Conditional deletion of Brf1 in gastrointestinal epithelial tissues, intestine, liver and pancreas, was incompatible with organ homeostasis. Deletion of Brf1 in adult intestine and liver induced apoptosis. However, Brf1 heterozygosity neither had gross effects in these epithelia nor did it modify tumorigenesis in the intestine or pancreas. Overexpression of BRF1 rescued the phenotypes of Brf1 deletion in intestine and liver but was unable to initiate tumorigenesis. Thus, Brf1 and Pol-III activity are absolutely essential for normal homeostasis during development and in adult epithelia. However, Brf1 overexpression or heterozygosity are unable to modify tumorigenesis, suggesting a permissive, but not driving role for Brf1 in the development of epithelial cancers of the pancreas and gut

Abstract B13: EGF/Ras/Erk signaling controls growth and proliferation through regulation of tRNA synthesis

Abstract Ras signaling promotes growth and proliferation in many tissues throughout animal development. An important challenge is to identify how the Ras-Erk pathway alters cellular metabolism to drive growth. Here we report on the control of tRNA synthesis as growth effector of EGF/Ras/Erk signaling in Drosophila. I find that overexpression of oncogenic Ras (RasV12) leads to increased mRNA translation and protein content in Drosophila S2 cells, suggesting that Ras may promote growth through enhanced protein synthesis. The conventional view is that the Ras pathway functions by controlling translation initiation factor activity. However I have identified an alternate mechanism involving control of tRNA synthesis. My data suggest that overexpression of RasV12 or the activated versions of EGFR and the Raf1 in wing imaginal discs increases tRNA synthesis. Similarly, expression of RasV12 in S2 cells increases tRNA levels, while blocking Ras/Erk signaling using the MEK inhibitor, U0126 or RNAi reduces tRNA synthesis. We previously identified the RNA polymerase III (Pol III) factor, Brf, as regulator of cell and tissue growth in Drosophila. Here we show that knockdown of either Brf blocks the effects of Ras signaling on growth and proliferation in larval wing imaginal discs, adult midgut progenitor cells and adult intestinal stem cells. Several transcription factors have been shown to link Ras signaling to changes in mRNA expression and growth. I have identified Myc is required but not sufficient for Ras-induced cell proliferation and growth through tRNA synthesis. Previously we have shown that TOR signaling regulates protein synthesis through RNA Pol III repressor, Maf1. I found that Maf1 RNAi increases tRNA synthesis in S2 cells. In addition, the decrease in tRNA synthesis induced by the MEK inhibitor is blocked in the presence of Maf1 RNAi suggesting Maf1 is downstream of Ras signaling pathway. My data point to control of tRNA synthesis possibly through Myc and/or Maf1 as a new mechanisms by which Ras signaling enhances protein synthesis to promote cell and tissue growth. Citation Format: Shrivani Sriskanthadevan-Pirahas, Savraj S. Grewal. EGF/Ras/Erk signaling controls growth and proliferation through regulation of tRNA synthesis. [abstract]. In: Proceedings of the AACR Special Conference on Translational Control of Cancer: A New Frontier in Cancer Biology and Therapy; 2016 Oct 27-30; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2017;77(6 Suppl):Abstract nr B13.</jats:p

Ras/ERK-signalling promotes tRNA synthesis and growth via the RNA polymerase III repressor Maf1 in Drosophila.

The small G-protein Ras is a conserved regulator of cell and tissue growth. These effects of Ras are mediated largely through activation of a canonical RAF-MEK-ERK kinase cascade. An important challenge is to identify how this Ras/ERK pathway alters cellular metabolism to drive growth. Here we report on stimulation of RNA polymerase III (Pol III)-mediated tRNA synthesis as a growth effector of Ras/ERK signalling in Drosophila. We find that activation of Ras/ERK signalling promotes tRNA synthesis both in vivo and in cultured Drosophila S2 cells. We also show that Pol III function is required for Ras/ERK signalling to drive proliferation in both epithelial and stem cells in Drosophila tissues. We find that the transcription factor Myc is required but not sufficient for Ras-mediated stimulation of tRNA synthesis. Instead we show that Ras signalling promotes Pol III function and tRNA synthesis by phosphorylating, and inhibiting the nuclear localization and function of the Pol III repressor Maf1. We propose that inhibition of Maf1 and stimulation of tRNA synthesis is one way by which Ras signalling enhances protein synthesis to promote cell and tissue growth

Ras/ERK-signalling promotes tRNA synthesis and growth via the RNA polymerase III repressor Maf1 in<i>Drosophila</i>

ABSTRACTThe small G-protein Ras is a conserved regulator of cell and tissue growth. These effects of Ras are mediated largely through activation of a canonical RAF-MEK-ERK kinase cascade. An important challenge is to identify how this Ras/ERK pathway alters cellular metabolism to drive growth. Here we report on stimulation of RNA polymerase III (Pol III)-mediated tRNA synthesis as a growth effector of Ras/ERK signalling inDrosophila. We find that activation of Ras/ERK signalling promotes tRNA synthesis both in vivo and in culturedDrosophilaS2 cells. We also show that Pol III function is required for Ras/ERK signalling to drive proliferation in both epithelial and stem cells inDrosophilatissues. We find that the transcription factor Myc is required but not sufficient for Ras-mediated stimulation of tRNA synthesis. Instead we show that the main way that Ras promotes Pol III function and tRNA synthesis is by inhibiting the nuclear localization and function of the Pol III repressor Maf1. We propose that inhibition of Maf1 and stimulation of tRNA synthesis is one way by which Ras signalling enhances protein synthesis to promote cell and tissue growth.</jats:p

Solution structures of the adhesion molecule DdCAD-1 reveal new insights into Ca2+-dependent cell-cell adhesion

10.1038/nsmb1162Nature Structural and Molecular Biology13111016-1022NSMB

Adipose mitochondrial metabolism controls body growth by modulating cytokine and insulin signaling

SummaryAnimals need to adapt their growth to fluctuations in nutrient availability to ensure proper development and survival. These adaptations often rely on specific nutrient-sensing tissues and their control of whole-body physiology through inter-organ communication. While the signaling mechanisms that underlie this communication are well studied, the contributions of metabolic alterations in the nutrient-sensing tissues are less clear. Here, we show how reprogramming of adipose mitochondrial metabolism controls whole-body growth in Drosophila larvae. We find that dietary nutrients alter fat body mitochondrial morphology to lower their bioenergetic activity, which we see can rewire fat body glucose metabolism. Strikingly, we find that genetic reduction of mitochondrial bioenergetics just in the fat body is sufficient to accelerate body growth and development. These growth effects are caused by inhibition of the fat-derived adipokine, TNFα/Eiger, which leads to enhanced systemic insulin signaling, the main hormonal stimulator of body growth. Our work reveals how reprogramming of mitochondrial metabolism in one nutrient-sensing tissue is able to couple whole body growth to nutrient availability.</jats:p

Mitochondrial metabolism in<i>Drosophila</i>macrophage-like cells regulates body growth via modulation of cytokine and insulin signaling

SummaryMacrophages play key roles in regulating and maintaining tissue and whole-body metabolism in both normal and disease states. While the cell-cell signaling pathway that underlie these functions are becoming clear, less is known about how alterations in macrophage metabolism influence their roles as regulators of systemic physiology. Here we investigate this by examining Drosophila macrophage-like cells called hemocytes. We used knockdown of TFAM, a mitochondrial genome transcription factor, to reduce mitochondrial OxPhos activity specifically in larval hemocytes. We find that this reduction in hemocyte OxPhos leads to a decrease in larval growth and body size. These effects are associated with a suppression of systemic insulin, the main endocrine stimulator of body growth. We also find that TFAM knockdown leads to decreased hemocyte JNK signaling and decreased expression of the TNF alpha homolog, Eiger in hemocytes. Furthermore, we show that genetic knockdown of hemocyte JNK signaling or Eiger expression mimics the effects of TFAM knockdown and leads to a non-autonomous suppression of body size but without altering hemocyte numbers. Our data suggest that modulation of hemocyte mitochondrial metabolism can determine their non-autonomous effects on organismal growth by altering cytokine and systemic insulin signaling. Given that mitochondrial metabolism can be controlled by nutrient availability, our findings may explain how macrophages function as nutrient-responsive regulators of tissue and whole-body physiology and homeostasis.</jats:p