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Julia von Blume, PhD

Associate Professor in Cell Biology
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About

Titles

Associate Professor in Cell Biology

Biography

Julia von Blume completed her Ph.D. in 2006 at the University of Ulm, Germany, focusing on investigating the cell compartment-specific functions of Protein Kinase D (PKD). During postdoctoral work at institutions including the University of California San Diego and the Center of Genomic Regulation (CRG) in Spain, she uncovered how cells organize and transport constitutively secreted proteins.

Continuing her research trajectory in 2012, she assumed an independent group leader position at the Max Planck Institute of Biochemistry in Martinsried (MPI-B), Germany. At MPI-B, her research group combined in vitro reconstitution experiments with advanced cell biology techniques to reveal autonomous molecular mechanisms devoid of cargo receptors. A significant discovery emerged: luminal Golgi resident protein Cab45 forms a scaffold within the trans-Golgi network (TGN) to package secretory proteins, driven by transient luminal Ca2+ increases.

In 2019, Julia von Blume relocated from Germany to the US, joining the Department of Cell Biology at Yale School of Medicine. Within this new academic home, her research broadened its scope to unravel the intricacies of insulin granule biogenesis in pancreatic beta cells. Key to this process is chromogranin B, which orchestrates the generation of a condensed protein scaffold at the moderately acidic pH of the TGN. This scaffold captures insulin and its processing enzymes, facilitating the budding of nascent insulin granules from the TGN. Drawing parallels to immune cells like neutrophils and mast cells that generate diverse secretory granules, the research poses a compelling question: Do granule-forming factors also exist in hematopoietic cells? Interestingly, chromogranin B, a player in insulin-secreting cells, prompts a similar line of inquiry.

Appointments

Education & Training

Postdoctoral Fellow
Centre Regulació Genòmica (2011)
Postdoctoral Fellow
University of California, San Diego (2007)
PhD
Ulm University (2006)
MSc
Konstanz University

Research

Overview

How are secretory proteins sorted and targeted to the cell surface?

Most secreted proteins contain a signal sequence that targets them to the endoplasmic reticulum (ER) during synthesis. There they are translocated into the ER lumen and once folded travel in coat complex II (COPII)-coated vesicles to the Golgi apparatus. After passage through the Golgi membranes, proteins are sorted at the TGN for transport to their final destination. Depending on the cell types these destinations include apical and basolateral cell surfaces, early/sorting endosomes, late endosomes, recycling endosomes, secretory storage granules and preceding Golgi compartments. Sorting of lysosomal hydrolases for delivery to pre-lysosomes is well established, the corresponding mechanism by which secreted proteins are sorted for transport to the plasma membrane is poorly understood.

  • Ca2+ dependent sorting in the trans-Golgi Network
  • The interconnection between Ca2+ dependent sorting and leukocyte trafficking
  • Novel Ca2+ independent sorting pathways

In recent years we discovered a novel sorting mechanism of secretory proteins a process that had remained mysterious for decades. The major components regulating this process are F-actin, cofilin, the Golgi ATPase SPCA1, Ca2+, and Cab45. We reconstituted the binding of cofilin to SPCA1 that recruits F-actin to a specific domain to initiate a Ca2+ influx required for cargo sorting Next, we discovered how a Golgi resident protein Cab45 binds and sorts cargo molecules by selective Ca2+ dependent oligomerization. This discovery led to the critical concept of sorting of proteins independent of a classical sorting receptor. Our research focuses on the poorly understood sorting reactions in the trans-Golgi Network (TGN) with particular emphasis on the role of protein and lipid complexes that recognize and pack secreted proteins into specific transport carriers. This process is crucial to facilitate secretion and function of these proteins in different cell types and organisms. Moving forward, we plan to identify the molecular mechanisms facilitating Ca2+ dependent sorting applying a combination of cell-based experiments, high-end microscopy, and biochemical reconstitution assays. To further investigate the link between TGN dependent sorting and physiology such as diabetes, we will apply mouse models.

A second major research goal of the group is the investigation of the interconnection of Ca2+ dependent sorting and cell migration in leukocytes. Leukocyte trafficking positions immune cells in the body and therefore has a central role in the function of the immune system. The foundation of these studies is that Cab45 and SPCA1 are primary regulators of extravasation of leukocytes. Leukocyte extravasation requires the sorting and transport of a so far unknown specific set of soluble molecules in the TGN. We plan to identify and analyze the secretomes of primary leukocytes isolated from SPCA1 and Cab45 knock-out mice. Having identified these factors, we will reconstitute their sorting using biochemical assays to gain an insight into the molecular complex in the TGN that together with Cab45 steers this process. Moving forward, we will be able to monitor the significance of Cab45, SPCA1 and the new components for extravasation of leukocytes in living organisms using intravital microscopy. These experiments will give mechanistic insight into the importance of TGN sorting for macrophage extravasation and will thus explain the basic mechanism of innate immunity.

In a third approach, we investigate additional mechanisms of TGN based secretory cargo sorting. For instance, our unpublished work has shown that sorting of Matrix Metallo Proteinases (MMPs) to podosomes in macrophages occurs in independently of our Ca2+-dependent sorting. We have accomplished to identify novel sorting regulators required for the transport of MMP2 to podosomes. To monitor and investigate the role of a physiological system we generated estrogen-regulated Hoxb8 immortalized macrophages in which we use CRISPR/Cas9 deplete these components. This system will allow monitoring the trafficking of MMP2 in macrophages and will also enable to track their movement in living organisms. These data will give an insight into the relevance of sorting of proteins inside macrophages and will allow testing their role in matrix invasion in normal and cancer tissues.

Research at a Glance

Yale Co-Authors

Frequent collaborators of Julia von Blume's published research.

Publications

2024

2023

2022

2021

Academic Achievements & Community Involvement

  • honor

    Rudolph J. Anderson Endowed Postdoctoral Fellowship

  • honor

    Pilot and Feasibility Award

  • honor

    Heisenberg Award

  • honor

    Perspective Program PLUS3 Award

  • honor

    Project Leader Collaborative Research Center 914

Get In Touch

Contacts

Academic Office Number
Mailing Address

Cell Biology

333 Cedar Stree1

New Haven, CT 06510

United States