bims-tubesc 2022-12-25 papers

bims-tubesc

Biomed News

on Molecular mechanisms in tuberous sclerosis

Issue of 2022–12–25
eight papers selected by

Drug Inhibition of Redox Factor-1 Restores Hypoxia-Driven Changes in Tuberous Sclerosis Complex 2 Deficient Cells.
mTORC1 regulates a lysosome-dependent adaptive shift in intracellular lipid species.
Ring domains are essential for GATOR2-dependent mTORC1 activation.
mTOR Signaling Network in Cell Biology and Human Disease.
mTORC1 takes control of lysosomal lipid breakdown.
Nuclear S6K1 Enhances Oncogenic Wnt Signaling by Inducing Wnt/β-Catenin Transcriptional Complex Formation.
Ras-mediated activation of mTORC2 promotes breast epithelial cell migration and invasion.
Zinc-finger Protein CXXC5 Promotes Breast Carcinogenesis by Regulating the TSC1/mTOR Signaling Pathway.

Cancers (Basel). 2022 Dec 15. pii: 6195. [Epub ahead of print]14(24):

Drug Inhibition of Redox Factor-1 Restores Hypoxia-Driven Changes in Tuberous Sclerosis Complex 2 Deficient Cells.

Jesse D Champion, Kayleigh M Dodd, Hilaire C Lam, Mohammad A M Alzahrani, Sara Seifan, Ellie Rad, David Oliver Scourfield, Melissa L Fishel, Brian L Calver, Ann Ager, Elizabeth P Henske, David Mark Davies, Mark R Kelley, Andrew R Tee.

  Therapies with the mechanistic target of rapamycin complex 1 (mTORC1) inhibitors are not fully curative for tuberous sclerosis complex (TSC) patients. Here, we propose that some mTORC1-independent disease facets of TSC involve signaling through redox factor-1 (Ref-1). Ref-1 possesses a redox signaling activity that stimulates the transcriptional activity of STAT3, NF-kB, and HIF-1α, which are involved in inflammation, proliferation, angiogenesis, and hypoxia, respectively. Here, we demonstrate that redox signaling through Ref-1 contributes to metabolic transformation and tumor growth in TSC cell model systems. In TSC2-deficient cells, the clinically viable Ref-1 inhibitor APX3330 was effective at blocking the hyperactivity of STAT3, NF-kB, and HIF-1α. While Ref-1 inhibitors do not inhibit mTORC1, they potently block cell invasion and vasculature mimicry. Of interest, we show that cell invasion and vasculature mimicry linked to Ref-1 redox signaling are not blocked by mTORC1 inhibitors. Metabolic profiling revealed that Ref-1 inhibitors alter metabolites associated with the glutathione antioxidant pathway as well as metabolites that are heavily dysregulated in TSC2-deficient cells involved in redox homeostasis. Therefore, this work presents Ref-1 and associated redox-regulated transcription factors such as STAT3, NF-kB, and HIF-1α as potential therapeutic targets to treat TSC, where targeting these components would likely have additional benefits compared to using mTORC1 inhibitors alone.

Keywords:  APE1; HIF-1α; NF-kB; Ref-1; STAT3; TSC; angiogenesis; hypoxia; mTOR; redox

DOI:  https://doi.org/10.3390/cancers14246195
Nat Metab. 2022 Dec;4(12): 1792-1811

mTORC1 regulates a lysosome-dependent adaptive shift in intracellular lipid species.

Aaron M Hosios, Meghan E Wilkinson, Molly C McNamara, Krystle C Kalafut, Margaret E Torrence, John M Asara, Brendan D Manning.

The mechanistic target of rapamycin complex 1 (mTORC1) senses and relays environmental signals from growth factors and nutrients to metabolic networks and adaptive cellular systems to control the synthesis and breakdown of macromolecules; however, beyond inducing de novo lipid synthesis, the role of mTORC1 in controlling cellular lipid content remains poorly understood. Here we show that inhibition of mTORC1 via small molecule inhibitors or nutrient deprivation leads to the accumulation of intracellular triglycerides in both cultured cells and a mouse tumor model. The elevated triglyceride pool following mTORC1 inhibition stems from the lysosome-dependent, but autophagy-independent, hydrolysis of phospholipid fatty acids. The liberated fatty acids are available for either triglyceride synthesis or β-oxidation. Distinct from the established role of mTORC1 activation in promoting de novo lipid synthesis, our data indicate that mTORC1 inhibition triggers membrane phospholipid trafficking to the lysosome for catabolism and an adaptive shift in the use of constituent fatty acids for storage or energy production.

DOI: https://doi.org/10.1038/s42255-022-00706-6
Mol Cell. 2022 Dec 08. pii: S1097-2765(22)01134-0. [Epub ahead of print]

Ring domains are essential for GATOR2-dependent mTORC1 activation.

Cong Jiang, Xiaoming Dai, Shaohui He, Hongfei Zhou, Lan Fang, Jianping Guo, Songlei Liu, Tao Zhang, Weijuan Pan, Haihong Yu, Tianmin Fu, Dali Li, Hiroyuki Inuzuka, Ping Wang, Jianru Xiao, Wenyi Wei.

  The GATOR2-GATOR1 signaling axis is essential for amino-acid-dependent mTORC1 activation. However, the molecular function of the GATOR2 complex remains unknown. Here, we report that disruption of the Ring domains of Mios, WDR24, or WDR59 completely impedes amino-acid-mediated mTORC1 activation. Mechanistically, via interacting with Ring domains of WDR59 and WDR24, the Ring domain of Mios acts as a hub to maintain GATOR2 integrity, disruption of which leads to self-ubiquitination of WDR24. Physiologically, leucine stimulation dissociates Sestrin2 from the Ring domain of WDR24 and confers its availability to UBE2D3 and subsequent ubiquitination of NPRL2, contributing to GATOR2-mediated GATOR1 inactivation. As such, WDR24 ablation or Ring deletion prevents mTORC1 activation, leading to severe growth defects and embryonic lethality at E10.5 in mice. Hence, our findings demonstrate that Ring domains are essential for GATOR2 to transmit amino acid availability to mTORC1 and further reveal the essentiality of nutrient sensing during embryonic development.

Keywords:  Gator1; Gator2; NPRL2; Sestrin; WDR24; amino acid sensing; mTOR; ubiquitination

DOI:  https://doi.org/10.1016/j.molcel.2022.11.021
Int J Mol Sci. 2022 Dec 18. pii: 16142. [Epub ahead of print]23(24):

mTOR Signaling Network in Cell Biology and Human Disease.

Jane J Yu, Elena A Goncharova.

The mechanistic target of rapamycin (mTOR) is a serine/threonine protein kinase that regulates multiple processes, including gene transcription, protein synthesis, ribosome biogenesis, autophagy, cell metabolism, and cell growth [...].

DOI: https://doi.org/10.3390/ijms232416142
Nat Metab. 2022 Dec;4(12): 1620-1622

mTORC1 takes control of lysosomal lipid breakdown.

Laura Tribouillard, Mathieu Laplante.

DOI: https://doi.org/10.1038/s42255-022-00702-w
Int J Mol Sci. 2022 Dec 18. pii: 16143. [Epub ahead of print]23(24):

Nuclear S6K1 Enhances Oncogenic Wnt Signaling by Inducing Wnt/β-Catenin Transcriptional Complex Formation.

Min Gyu Lee, Hwamok Oh, Jong Woo Park, Jueng Soo You, Jeung-Whan Han.

  Ribosomal protein S6 kinase 1 (S6K1), a key downstream effector of the mammalian target of rapamycin (mTOR), regulates diverse functions, such as cell proliferation, cell growth, and protein synthesis. Because S6K1 was previously known to be localized in the cytoplasm, its function has been mainly studied in the cytoplasm. However, the nuclear localization and function of S6K1 have recently been elucidated and other nuclear functions are expected to exist but remain elusive. Here, we show a novel nuclear role of S6K1 in regulating the expression of the Wnt target genes. Upon activation of the Wnt signaling, S6K1 translocated from the cytosol into the nucleus and subsequently bound to β-catenin and the cofactors of the Wnt/β-catenin transcriptional complex, leading to the upregulation of the Wnt target genes. The depletion or repression of S6K1 downregulated the Wnt target gene expression by inhibiting the formation of the Wnt/β-catenin transcriptional complex. The S6K1-depleted colon cancer cell lines showed lower transcription levels of the Wnt/β-catenin target genes and a decrease in the cell proliferation and invasion compared to the control cell lines. Taken together, these results indicate that nuclear S6K1 positively regulates the expression of the Wnt target genes by inducing the reciprocal interaction of the subunits of the transcriptional complex.

Keywords:  Wnt signaling; Wnt-transcriptional complex; mTOR; p70 S6K1; β-catenin

DOI:  https://doi.org/10.3390/ijms232416143
Mol Biol Cell. 2022 Dec 21. mbcE22060236

Ras-mediated activation of mTORC2 promotes breast epithelial cell migration and invasion.

Shannon E Collins, Mollie E Wiegand, Alyssa N Werner, Isabella N Brown, Mary I Mundo, Douglas J Swango, Ghassan Mouneimne, Pascale G Charest.

We previously identified the mechanistic Target of Rapamycin Complex 2 (mTORC2) as an effector of Ras for the control of directed cell migration in Dictyostelium. Recently, the Ras-mediated regulation of mTORC2 was found to be conserved in mammalian cells, and mTORC2 was shown to be an effector of oncogenic Ras. Interestingly, mTORC2 has been linked to cancer cell migration, and particularly in breast cancer. Here, we investigated the role of Ras in promoting the migration and invasion of breast cancer cells through mTORC2. We observed that both Ras and mTORC2 promote the migration of different breast cancer cells and breast cancer cell models. Using HER2 and oncogenic Ras-transformed breast epithelial MCF10A cells, we found that both wild-type Ras and oncogenic Ras promote mTORC2 activation and an mTORC2-dependent migration and invasion in these breast cancer models. We further observed that, whereas oncogenic Ras-transformed MCF10A cells display uncontrolled cell proliferation and invasion, disruption of mTORC2 leads to loss of invasiveness only. Together, our findings suggest that, whereas the Ras-mediated activation of mTORC2 is expected to play a minor role in breast tumor formation, the Ras-mTORC2 pathway plays an important role in promoting the migration and invasion of breast cancer cells.

DOI: https://doi.org/10.1091/mbc.E22-06-0236
J Biol Chem. 2022 Dec 17. pii: S0021-9258(22)01255-8. [Epub ahead of print] 102812

Zinc-finger Protein CXXC5 Promotes Breast Carcinogenesis by Regulating the TSC1/mTOR Signaling Pathway.

Wenjuan Wang, Zhaohan Zhang, Minghui Zhao, Yu Wang, Yuze Ge, Lin Shan.

CXXC5, a member of the CXXC family of zinc-finger proteins, is associated with numerous pathological processes. However, the pathophysiological function of CXXC5 has not been clearly established. Herein, we found that CXXC5 interacts with the CRL4B and NuRD complexes. Screening of transcriptional targets downstream of the CXXC5-CRL4B-NuRD complex by next-generation sequencing (ChIP-sequencing) revealed that the complex regulates the transcriptional repression process of a cohort of genes, including TSC1, that play important roles in cell growth and mTOR signaling pathway regulation, and whose abnormal regulation results in the activation of programmed cell death-ligand protein 1 (PD-L1). Intriguingly, CXXC5 expression increased after stimulation with vitamin B2, but decreased after vitamin D treatment. We also found that the CXXC5-CRL4B-NuRD complex promotes the proliferation of tumor cells in vitro and accelerates the growth of breast cancer in vivo. The expression of CXXC5, CUL4B, and MTA1 increased during the occurrence and development of breast cancer, and correspondingly, TSC1 expression decreased. Meanwhile, a high expression of CXXC5 was positively correlated with the histological grade of high malignancy and poor survival of patients. In conclusion, our study revealed that CXXC5-mediated TSC1 suppression activates the mTOR pathway, reduces autophagic cell death, induces PD-L1-mediated immune suppression, and results in tumor development, shedding light on the mechanism of the pathophysiological function of CXXC5.

DOI: https://doi.org/10.1016/j.jbc.2022.102812