# Mechanism of secretory cargo sorting at the trans-Golgi Network (TGN)

> **NIH NIH R35** · YALE UNIVERSITY · 2023 · $327,894

## Abstract

Project summary
Protein secretion plays a central role in developing and maintaining multicellular organisms. Specialized cell
types in tissues secrete proteins by regulated or constitutive secretion. Regulated secretion occurs in response
to an extracellular stimulus that elicits the release of signaling molecules, while constitutive secretion facilitates
the deposition of extracellular matrix components that provide tissue integrity. Even though these processes
are highly significant for human health, features that determine whether a protein is secreted by
regulated or constrictive secretion remain unknown. A central regulator of intracellular protein distribution
is the trans-Golgi Network (TGN), which sorts and packages secretory proteins into specific vesicular carriers
targeting them to intracellular storage granules (regulated secretion) or the cell surface (constitutive secretion).
The identification of the mannose-6-phosphate receptor (M6P-R) that recognizes M6P tags of lysosomal led to
the idea that specific sorting receptors also sort secretory proteins. However, conserved recognition signals
or cargo receptors remain unknown. How are these molecules recognized and sorted for targeting the
correct destination?
The concept of concentrating macromolecules into biomolecular condensates by liquid-liquid phase separation
(LLPS) has revolutionized modern cell biology. Human cells use this principle to organize biochemical
processes spatially without a membrane. Our recent research raises the novel possibility that the segregation
of secretory proteins in the TGN lumen follows this concept. Our work has shown that purified chromogranins
(CGs) or Cab45 undergo liquid-liquid phase separation (LLPS) in the milieu of TGN. Both proteins have been
suggested to co-aggregate with secreted proteins (clients) to facilitate their sorting and packaging. We show
that CG or Cab45 liquids, not solid aggregates, are essential for client sorting and packaging. Nonetheless,
the underlying mechanisms of LLPS-dependent client packaging remain elusive. Therefore, our long-term
goal is to understand the molecular basis of LLPS-dependent cargo sorting for regulated (by CGs) and
constitutive (by Cab45) secretion.
Our proposal aims at identifying the mechanisms of LLPS-dependent sorting in reconstituted systems that
recreate the milieu of the TGN lumen. We will include model membranes to examine if and how these
condensates associate with the luminal leaflet of the TGN. We will use cell culture models of regulated (P12
cells) or constitutive (skin fibroblasts) secretion to validate our in-vitro results in living cells. Our concept will
establish the molecular requirements for condensate formation, the mechanisms of client recognition and
vesicular formation in regulated and constitutive secretion. These results will provide a fundamental
understanding of an exciting new paradigm in cell biology and impact the research of pathologies
caused by defective protein secre...

## Key facts

- **NIH application ID:** 10623825
- **Project number:** 1R35GM149293-01
- **Recipient organization:** YALE UNIVERSITY
- **Principal Investigator:** Julia von Blume
- **Activity code:** R35 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2023
- **Award amount:** $327,894
- **Award type:** 1
- **Project period:** 2023-04-01 → 2028-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10623825

## Citation

> US National Institutes of Health, RePORTER application 10623825, Mechanism of secretory cargo sorting at the trans-Golgi Network (TGN) (1R35GM149293-01). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10623825. Licensed CC0.

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