Protein kinase D-mediated balance between lipid homeostasis and secretory activity in mammalian cells - A systemic appoach

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Lipid metabolism, sorting and transport between different organelles are tightly regulated in mammalian cells, since lipid homeostasis is critical for maintaining the integrities of cellular membranes. At the Golgi complex the lipid composition determines the formation of transport vesicles, which are required to shuffle secretory proteins from the trans-Golgi network (TGN) to the cell membrane. Protein kinase D (PKD) has been shown to play an important role in this regulation: Active PKD is directly involved in the fission of transport vesicles at the TGN. Furthermore, it has a dual function for the ceramide transport from the endoplasmic reticulum (ER) to the TGN by regulating the activity of the ceramide transfer protein (CERT) in two opposite ways. PKD and CERT mutually regulate each other in a complex structure of interrelated feedback circuits, making this system an attractive target for a holistic modeling approach. Moreover, recent advances in experimental techniques have led to new insights about molecular interactions at the TGN, and regulation of secretion has not yet been taken into account in theoretical secretion models. The goal of this project is to increase our understanding about the role of PKD in the balance between lipid homeostasis and secretion. This will be achieved by a data- and knowledge-driven modeling approach based on chemical reaction kinetics, which will be accompanied by perturbation experiments that are used for model identification. We will particularly focus on statistical methods for parameter estimation and model selection, identifiability analysis, and systems-theoretic methods to investigate coupled feedback. The results of our project will be highly relevant for biotechnological applications: We may reveal targets for optimization of mammalian host cell lines used for therapeutic protein production, where regulation processes at the TGN have recently been identified as a bottleneck in the secretory pathways.