1. Research Background:

Cell growth is a crucial and tightly regulated process. Cells take up nutrients (like amino acids, sugars, lipids) from their environment, and use them to synthesize various macromolecules, which they incorporate to increase their mass and grow. As growth is very energy consuming, cells have developed mechanisms to sense environmental conditions and to adjust their metabolism accordingly, so that they only grow when conditions are optimal. These mechanisms are of great importance, as dysregulation of growth can lead to life-threatening disorders, such as cancer and other age-related diseases. Our work focuses on the intricate molecular and cellular mechanisms of nutrient sensing and growth control, mainly via the regulation of the TSC/mTOR signaling hub. Given the central role of mTOR in the ageing process, and that dysregulation of the nutrient sensing machinery is a hallmark of ageing, our research investigates fundamental aspects of ageing and age-related diseases.

The mTOR kinase, as part of the mTOR complexes 1 (mTORC1) and 2 (mTORC2), is a master growth regulator. It functions as a sensor and a molecular rheostat that links information from the cellular milieu to the growth properties of the cells. A large number of inputs converge on mTORC1 to regulate growth. Nutrients, energy, and growth factors activate this complex, whereas various stresses strongly inhibit its activity. Besides cell growth, mTOR activity affects the majority of cellular functions and can therefore influence organismal health, lifespan and ageing. Importantly, mutations on upstream pathway components, such as the inhibitory Tuberous Sclerosis Complex (TSC) proteins, can lead to mTOR hyperactivation, and, thus, are clinically relevant. In line with this, compounds targetingmTOR or upstream regulatory components are currently being used against various diseases or as anti-ageing drugs.

2. Research questions addressed by the group:

control, mainly via the regulation of the master cellular nutrient sensor and growth coordinator, the mTOR kinase; and of its main negative upstream regulator, the TSC complex. We have previously elucidated the mechanistic details of mTOR inactivation in response to nutrient starvation and have revealed how information from multiple, diverse, cellular stresses is integrated to control cellular physiology. The vision of the Demetriades group at the MPI-AGE is to understand:

• how cells sense the presence or the absence of nutrients in their environment to adjust their growth and metabolism accordingly,
• how the dysregulation of these cellular mechanisms contributes to the development of human diseases (cancer, diabetes, neurological disorders) and the ageing process, and
• how we can intervene pharmacologically to target these mTOR-related conditions.

3. Possible project(s):

Multiple projects are available in the lab for the prospective PhD students, for most of which we already have intriguing preliminary results. Our philosophy is that each person should have a tailored project based on his/her technical skills and research background, so that he/she is maximally efficient. Although it does not cover the full array of research taking place in our lab, an indicative list is provided here:

• Novel molecular players and mechanisms in amino acid sensing by mTORC1.
• Role of ubiquitination of mTOR in cell growth, skin biology and cancer.
• Spatiotemporal regulation of the TSC complex in starvation and stress.
• Pathways of bulky cargo secretion and their role in skeletal disease.
• Principles of cargo sorting at the Golgi and its role in inter-organellar communication.
• Development of novel, specific mTORC1 inhibitors.

4. Applied Methods and model organisms:

We apply high-throughput omics (functional genomic screens, proteomics, metabolomics) to identify novel regulators of key cellular processes; and combine them with state-of-the-art molecular biology, biochemistry, cell biology, and high-resolution microscopy techniques to understand the very mechanistic details of their function and to reveal new principles in nutrient sensing and cell growth research. We use various established human and mouse cell lines to identify evolutionarily conserved processes and to address multiple fundamental questions. Our group also implements patient-derived cell lines to study the disease relevance of our findings. When necessary, we use advanced CRISPR-based gene-editing techniques to generate custom-made knock-out/transgenic cell lines. In order to investigate how our genes of interest affect organismal physiology, behavior, health, and ageing, we often transfer our findings to the mouse model using wild-type or knock-out animals.

5. Desirable skills and qualifications:

The applicant is required to hold a master’s degree/diploma in biology, biochemistry or a related field, and to have strong written and oral communication skills. The working language of the lab is English; knowledge of the Germanlanguage is not necessary. Experience in one or more of the following methodologies: cell culture, confocal microscopy, protein (western blotting, immunoprecipitation) and RNA analysis (RT-qPCR), mass-spectrometry, gene- editing, or previous work with mouse models is an advantage.

We seek for highly-motivated, hard-working, ambitious, talented students to join an enthusiastic international research team. Independent thinking and ability to work both independently and as part of a team is a plus.

6. References:

• Gollwitzer P.*, Grützmacher N.*, Wilhelm S., Kümmel D., and Demetriades C., A Rag GTPase Dimer Code Defines the Regulation of mTORC1 by Amino Acids. Nat Cell Biol. 2022 (in press)
• Huang W.*, Kew C.*, Fernandes SA., Loerhke A., Han L., Demetriades C., and Antebi A., Decreased spliceosome fidelity and egl-8 intron retention inhibit mTORC1 signaling to promote longevity. Nat Aging. 2022 (in press)
• Fernandes AS. and Demetriades C., The Multifaceted Role of Nutrient Sensing and mTORC1 Signaling in Physiology and Aging. Front. Aging. 2021 August 27. doi:10.3389/fragi.2021.707372
• Nüchel J., Tauber M., Nolte JL., Mörgelin M., Türk C., Eckes B., Demetriades C.^#, and Plomann M.^#, A novel mTORC1-GRASP55 signaling axis reshapes the extracellular proteome upon stress. Mol Cell. 2021 Jul 5;S1097-2765(21)00497-4. doi: 10.1016/j.molcel.2021.06.017.
• Demetriades C. ^#, Nüchel J., and Plomann M. ^#, GRASPing the unconventional secretory machinery to bridge cellular stresssignaling to the extracellular proteome. Cell Stress. 2021 Oct 15;5(11): 173-175. doi: 10.15698/cst2021.11.259
• Fitzian K.*, Brückner A.*, Brohée L.*, Zech R., Antoni C., Kiontke S., Gasper R., Linard Matos AL., Beel S., Wilhelm S., Gerke V., Ungermann C., Nellist M., Raunser S., Demetriades C.^#, Oeckinghaus A.^#, and Kümmel D.^#, TSC1 binding to lysosomal PIPs is required for TSC complex translocation and mTORC1 regulation. Mol Cell. 2021 Jul 1;81(13):2705-2721.e8.
• Prentzell MT., Rehbein U., Cadena Sandoval M., et al., G3BPs tether the TSC complex to lysosomes and suppress mTORC1 signaling. Cell. 2021 Feb 4;184(3):655-674.e27.
• Romero-Pozuelo J., Demetriades C., Schroeder P., and Teleman AA., CycD/Cdk4 and discontinuities in Dpp signaling activate TORC1 in the Drosophila wing disc. Developmental Cell. 2017 Aug 21;42(4):376-387.e5.
• Tsokanos F.*, Albert MA.*, Demetriades C.*, Spirohn K., Boutros M., and Teleman AA., eIF4A inactivates TORC1 in response to amino acid starvation. EMBO J. 2016 Mar 17;35(10):1058-76.
• Demetriades C.^#, Plescher M., and Teleman AA.^#, Lysosomal recruitment of TSC2 is a universal response to cellular stress. Nature Communications. 2016 Feb 12;7:10662.
• Plescher M., Teleman AA.^#, and Demetriades C.^#, TSC2 mediates hyperosmotic stress-induced inactivation of mTORC1. Scientific Reports. 2015 Sep 8;5:13828.
• Demetriades C.^#, Doumpas N., and Teleman AA.^#, Regulation of TORC1 in response to amino acid starvation via lysosomal recruitment of TSC2. Cell. 2014 February; 156(4):786-99.

* Co-first authors
# Co-corresponding authors