Joseph G. Moloughney

Poloxamer 188 (P188) as a Membrane Resealing Reagent in Biomedical Applications

Maintenance of the integrity of the plasma membrane is essential for maintenance of cellular function and prevention of cell death. Since the plasma membrane is frequently exposed to a variety of mechanical and chemical insults the cell has evolved active processes to defend against these injuries by resealing disruptions in the plasma membrane. Cell membrane repair is a conserved process observed in nearly every cell type where intracellular vesicles are recruited to sites of membrane disruption where they can fuse with themselves or the plasma membrane to create a repair patch. When disruptions are extensive or there is an underlying pathology that reduces the membrane repair capacity of a cell this defense mechanism may prove insufficient and the cell could die due to breakdown of the plasma membrane. Extensive loss of cells can compromise the integrity and function of tissues and leading to disease. Thus, methods to increase membrane resealing capacity could have broad utility in a number of disease states. Efforts to find reagents that can modulate plasma membrane reseal found that specific tri-block copolymers, such as poloxamer 188 (P188, or Pluronic F68), can increase the structural stability and resealing of the plasma membrane. Here we review several current patents and patent applications that present inventions making use of P188 and other copolymers to treat specific disease states such as muscular dystrophy, heart failure, neurodegenerative disorders and electrical injuries, or to facilitate biomedical applications such as transplantation. There appears to be promise for the application of poloxamers in the treatment of various diseases, however there are potential concerns with toxicity with long term application and bioavailability in some cases.

Vaccinia virus leads to ATG12–ATG3 conjugation and deficiency in autophagosome formation

The interactions between viruses and cellular autophagy have been widely reported. On the one hand, autophagy is an important innate immune response against viral infection. On the other hand, some viruses exploit the autophagy pathway for their survival and proliferation in host cells. Vaccinia virus is a member of the family of Poxviridae which includes the smallpox virus. The biogenesis of vaccinia envelopes, including the core envelope of the immature virus (IV), is not fully understood. In this study we investigated the possible interaction between vaccinia virus and the autophagy membrane biogenesis machinery. Massive LC3 lipidation was observed in mouse fibroblast cells upon vaccinia virus infection. Surprisingly, the vaccinia virus induced LC3 lipidation was shown to be independent of ATG5 and ATG7, as the atg5 and atg7 null mouse embryonic fibroblasts (MEFs) exhibited the same high levels of LC3 lipidation as compared with the wild-type MEFs. Mass spectrometry and immunoblotting analyses revealed that the viral infection led to the direct conjugation of ATG3, which is the E2-like enzyme required for LC3-phosphoethanonamine conjugation, to ATG12, which is a component of the E3-like ATG12–ATG5-ATG16 complex for LC3 lipidation. Consistently, ATG3 was shown to be required for the vaccinia virus induced LC3 lipidation. Strikingly, despite the high levels of LC3 lipidation, subsequent electron microscopy showed that vaccinia virus-infected cells were devoid of autophagosomes, either in normal growth medium or upon serum and amino acid deprivation. In addition, no autophagy flux was observed in virus-infected cells. We further demonstrated that neither ATG3 nor LC3 lipidation is crucial for viral membrane biogenesis or viral proliferation and infection. Together, these results indicated that vaccinia virus does not exploit the cellular autophagic membrane biogenesis machinery for their viral membrane production. Moreover, this study demonstrated that vaccinia virus instead actively disrupts the cellular autophagy through a novel molecular mechanism that is associated with aberrant LC3 lipidation and a direct conjugation between ATG12 and ATG3.

Mammalian Target of Rapamycin Complex 2 Modulates αβTCR Processing and Surface Expression during Thymocyte Development

An efficient immune response relies on the presence of T cells expressing a functional TCR. Whereas the mechanisms generating TCR diversity for antigenic recognition are well defined, what controls its surface expression is less known. In this study, we found that deletion of the mammalian target of rapamycin complex (mTORC) 2 component rictor at early stages of T cell development led to aberrant maturation and increased proteasomal degradation of nascent TCRs. Although CD127 expression became elevated, the levels of TCRs as well as CD4, CD8, CD69, Notch, and CD147 were significantly attenuated on the surface of rictor-deficient thymocytes. Diminished expression of these receptors led to suboptimal signaling, partial CD4−CD8− double-negative 4 (CD25−CD44−) proliferation, and CD4+CD8+ double-positive activation as well as developmental blocks at the CD4−CD8− double-negative 3 (CD25+CD44−) and CD8–immature CD8+ single-positive stages. Because CD147 glycosylation was also defective in SIN1-deficient fibroblasts, our findings suggest that mTORC2 is involved in the co/posttranslational processing of membrane receptors. Thus, mTORC2 impacts development via regulation of the quantity and quality of receptors important for cell differentiation.

Abstract 21: The mTORC2 target Akt is regulated in response to glutamine metabolite levels

Highly proliferating cells are particularly dependent on glucose and glutamine for bioenergetics and to fuel biosynthesis of macromolecules. The signals that respond to the fluctuations of these nutrients and how they control metabolic pathways remain poorly understood. mTOR, as part of mTOR complex 1 (mTORC1), responds to amino acids and plays a central role in metabolism. On the other hand, little is known on how mTORC2, consisting of the core components mTOR, rictor, SIN1 and mLST8 is regulated and its metabolic functions. The phosphorylation of the mTORC2 substrate, Akt, is enhanced in cancer cells, suggesting that mTORC2 becomes deregulated during tumorigenesis. Here we found that the activity of mTORC2 is enhanced by diminishing glutamine-derived metabolites. mTORC2 activity is required by glutamine-requiring biosynthetic pathways such as the hexosamine biosynthetic pathway (HBP). Acute nutrient withdrawal augments Akt phosphorylation but does not affect GFAT1 expression. However, extreme starvation that eventually depletes intracellular glutamine metabolites inactivates mTORC2 and downregulates GFAT1 expression. Thus, while mTORC1 senses glutamine abundance to promote anabolism, mTORC2 responds to declining glutamine catabolites in order to restore metabolic homeostasis. Our findings uncover the role of mTORC2 in metabolic reprogramming and provide insights on more effective therapeutic strategies for glutamine-dependent tumors. Citation Format: Estela Jacinto, Joseph Moloughney, Peter K. Kim, Nicole M. Vega-Cotto, Chang-Chih Wu, Thomas Lynch, Sisi Zhang, Matthew Adlam, Sai Guntaka, Po-Chien Chou, Joshua D. Rabinowitz, Guy Werlen. The mTORC2 target Akt is regulated in response to glutamine metabolite levels. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 21.

mTORC2 modulates the amplitude and duration of GFAT1 Ser243 phosphorylation to maintain flux through the hexosamine pathway during starvation

The mechanistic target of rapamycin (mTOR) controls metabolic pathways in response to nutrients. Recently, we have shown that mTOR complex 2 (mTORC2) modulates the hexosamine biosynthetic pathway (HBP) by promoting the expression of the key enzyme of the HBP, glutamine:fructose-6-phosphate aminotransferase 1 (GFAT1). Here, we found that GFAT1 Ser-243 phosphorylation is also modulated in an mTORC2-dependent manner. In response to glutamine limitation, active mTORC2 prolongs the duration of Ser-243 phosphorylation, albeit at lower amplitude. Blocking glycolysis using 2-deoxyglucose robustly enhances Ser-243 phosphorylation, correlating with heightened mTORC2 activation, increased AMPK activity, and O-GlcNAcylation. However, when 2-deoxyglucose is combined with glutamine deprivation, GFAT1 Ser-243 phosphorylation and mTORC2 activation remain elevated, whereas AMPK activation and O-GlcNAcylation diminish. Phosphorylation at Ser-243 promotes GFAT1 expression and production of GFAT1-generated metabolites including ample production of the HBP end-product, UDP-GlcNAc, despite nutrient starvation. Hence, we propose that the mTORC2-mediated increase in GFAT1 Ser-243 phosphorylation promotes flux through the HBP to maintain production of UDP-GlcNAc when nutrients are limiting. Our findings provide insights on how the HBP is reprogrammed via mTORC2 in nutrient-addicted cancer cells.

The mTOR Complexes in Cancer Cell Metabolism

Cells metabolize nutrients to generate energy and building materials for growth and proliferation. In highly proliferating cells, such as cancer cells, there is an increased demand for nutrients with concomitant rerouting of metabolic pathways in favor of biosynthetic processes. This rewiring is accomplished by cross talk between growth signaling and metabolic pathways. At the hub of these pathways is the mechanistic or mammalian target of rapamycin (mTOR), a protein kinase that senses nutrients and growth signals. mTOR forms two protein complexes, termed mTOR complex 1 (mTORC1) and mTORC2, by partnering with distinct proteins. Several studies strongly support a central role for mTORC1 in metabolic reprogramming but there is also emerging evidence for mTORC2 involvement in this process. This review focuses on the role of both complexes in different metabolic and biosynthetic processes in which they have been linked so far, with special emphasis on the role of mTORCs in cancer metabolic reprogramming. We also discuss the clinical relevance of targeting mTOR and metabolic pathways for cancer therapy.

Abstract 1150: mTORC2 enhances flux through the hexosamine biosynthetic pathway by regulation of GFAT1 expression

Metabolic and biosynthetic pathways drive cell growth and proliferation in response to nutrients and growth factors. Highly proliferating cells utilize glucose and glutamine to fuel biosynthetic processes. These two nutrients serve as substrates for the glutamine:fructose-6-phosphate amidotransferase (GFAT1), the rate-limiting enzyme in the hexosamine biosynthetic pathway (HBP), which ultimately produces UDP-GlcNAc that is necessary for protein glycosylation. Despite a role for the HBP in insulin resistance and lifespan extension, the mechanisms underlying GFAT1 regulation in vivo has remained elusive. We found mTOR complex 2 (mTORC2) controls flux through the HBP via regulation of GFAT1 expression levels in response to glucose. In the absence of mTORC2, GFAT1 expression is reduced and highly sensitive to glucose starvation. Furthermore, UDP-GlcNAc is highly diminished and glycosylation of specific transmembrane proteins such as CD147 is defective upon mTORC2 disruption. However, mTORC2 is also required for glycolysis and other biosynthetic pathways whose metabolites feed into the HBP. Thus, although exogenous UDP-GlcNAc can partially rescue glycosylation defects, it does not rescue the metabolic deficiencies in the absence of mTORC2. Like GFAT1, key enzymes of biosynthetic pathways have decreased expression in mTORC2-disrupted cells. Thus, by regulating levels of metabolic enzymes, mTORC2 coordinates flux through biosynthetic pathways in response to glucose availability. Our findings have implications for therapeutic targeting of mTORC2 in insulin resistance and cancer metabolism. Citation Format: Estela Jacinto, Joseph Moloughney, Thomas Lynch, Chang-Chih Wu, Olufunmilola Ibironke, Aixa Navia, Po-Chien Chou, Sisi Zhang, Joshua Rabinowitz, Guy Werlen. mTORC2 enhances flux through the hexosamine biosynthetic pathway by regulation of GFAT1 expression. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1150. doi:10.1158/1538-7445.AM2015-1150

Abstract 2441: mTOR complex 2 modulates glycosylation of CD147 via the hexosamine biosynthetic pathway

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Cell surface proteins transduce extracellular signals into the cell to control metabolism and growth. In turn, their expression is linked to nutrient availability and other growth signals by mechanisms that are poorly understood. The mammalian target of rapamycin (mTOR) regulates cell growth and metabolism and is part of two distinct protein complexes, mTOR complex 1 (mTORC1) and mTORC2. We found that mTORC2 is involved in the processing and maturation of cell surface receptors such as CD147. CD147 is a highly glycosylated receptor that has been linked to tumor progression via its role in activating matrix metalloproteinases and maturation of lactate transporters. In breast cancer cells, CD147 glycosylation is highly sensitive to glucose starvation and mTOR inhibition. In mTORC2-disrupted cells CD147 is misprocessed and occurs predominantly in a low glycosylated form. CD147 misprocessing can be partly rescued by addition of exogenous UDP-GlcNAc, the end product of the hexosamine biosynthetic pathway (HBP). However, UDP-GlcNAc cannot restore the abnormal growth and metabolism in mTORC2-disrupted cells due to defects in expression of other key metabolic enzymes in these cells. Our findings define a role for mTORC2 in regulating receptor glycosylation via the HBP and reveal a broader role for mTORC2 in controlling other biosynthetic pathways that become deregulated in cancer. Citation Format: Chang-Chih Wu, Thomas Lynch, Joseph Moloughney, Aixa Navia, Olufunmilola Ibironke, Po-Chien Chou, Nicole M. Vega-Cotto, Sisi Zhang, Joshua Rabinowitz, Guy Werlen, Estela Jacinto. mTOR complex 2 modulates glycosylation of CD147 via the hexosamine biosynthetic pathway. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2441. doi:10.1158/1538-7445.AM2014-2441