Biology subjects

Cavanagh, A. T.

Publications and source records attributed to Cavanagh, A. T..

5 recordsLinked to original sources

bioRxiv2026

Mechanistic dissection of BLTP2 targeting to ER-PM contact sites

The bridge-like lipid transfer proteins (BLTPs) are a novel superfamily of rod-shaped lipid transporters that engage in bulk non-vesicular movement of lipids at organelle membrane contact sites. The molecular and cellular functions of these proteins are still emerging; however, it is clear that one key aspect that regulates BLTP function is targeting to the appropriate membrane contact site(s). Here, we use Drosophila as a model system to dissect the mechanisms that drive targeting of BLTP2 (hobbit in Drosophila) to endoplasmic reticulum-plasma membrane (ER-PM) contact sites. We demonstrate that a conserved adapter protein, which we name bilbobaggins (bbo), is required for targeting of Hobbit to ER-PM contacts; importantly, loss of bbo phenocopies loss of hobbit, indicating that bbo is required for hobbit function. Additionally, our structure-function analyses show that cis-acting sequences in the C-terminal tail of Hobbit are also required for ER-PM targeting. Crucially, our data indicates that that these cis-acting sequences and Bbo binding are independent and likely sequential mechanisms that we propose function like a "hook" and "latch" to govern Hobbit targeting. Thus, we define a new regulatory paradigm governing targeting of BLTPs to membrane contact sites.

cell biology↗

bioRxiv2023

Modulation of hepatic transcription factor EB activity during cold exposure uncovers direct regulation of bis(monoacylglycerol)phosphate lipids by Pla2g15

Cold exposure is a selective environmental stress that elicits a rapid metabolic shift to maintain energy homeostasis. In response to cold exposure, the liver rewires the metabolic state shifting from glucose to lipid catabolism. By probing the liver lipids in cold exposure, we observed that the lysosomal bis(monoacylglycero)phosphate (BMP) lipids were rapidly increased during cold exposure. BMP lipid changes occurred independently of lysosomal abundance but were dependent on the lysosomal transcriptional regulator transcription factor EB (TFEB). Knockdown of TFEB in hepatocytes decreased BMP lipid levels and led to cold intolerance in mice. We assessed TFEB binding sites of lysosomal genes and determined that the phospholipase Pla2g15 regulates BMP lipid catabolism. Knockdown of Pla2g15 in mice increased BMP lipid levels, ablated the cold-induced rise, and improved cold tolerance. Knockout of Pla2g15 in mice and hepatocytes led to increased BMP lipid levels, that were decreased with re-expression of Pla2g15. Mutation of the catalytic site of Pla2g15 ablated the BMP lipid breakdown. Together, our studies uncover TFEB regulation of BMP lipids through Pla2g15 catabolism.

biochemistry↗

bioRxiv2021

The Hob proteins are novel and conserved lipid binding proteins at ER-PM contact site

Membrane contact sites are critical junctures for organelle signaling and communication. Endoplasmic reticulum-plasma membrane (ER-PM) contact sites were the first membrane contact sites to be described; however, the protein composition and molecular function of these sites is still emerging. Here, we leverage yeast and Drosophila model systems to uncover a novel role for the Hobbit/Hob proteins at ER-PM contact sites. We find that Hobbit localizes to ER-PM contact sites in both yeast cells and the Drosophila larval salivary glands, and this localization is mediated by an N-terminal ER membrane anchor and conserved C-terminal sequences. The C-terminus of Hobbit binds to plasma membrane phosphatidylinositols, and the distribution of these lipids is altered in hobbit mutant cells. Notably, the Hobbit protein is essential for viability in higher animals, providing one of the first examples of a membrane contact site-localized lipid binding protein that is required for development.

cell biology↗

bioRxiv2021

A novel function for Rab proteins during maturation of secretory granules

Regulated exocytosis is an essential process whereby professional secretory cells synthesize and secrete specific cargo proteins in a stimulus-dependent manner. Cargo-containing secretory granules are synthesized in the trans-Golgi Network (TGN); after budding from the TGN, granules undergo many modifications, including a dramatic increase in size. These changes occur during a poorly understood process called secretory granule maturation. Here we leverage the professional secretory cells of the Drosophila larval salivary glands as a model system to characterize a novel and unexpected role for Rab GTPases during secretory granule maturation. We find that secretory granules in the larval salivary glands increase in size ~300-fold between biogenesis and release, and loss of Rab1 or Rab11 dramatically reduces granule size. Surprisingly, we find that Rab1 and Rab11 protein localize to secretory granule membranes. Rab11 associates with granule membranes throughout the maturation process, and Rab11 is required for recruitment of Rab1. In turn, Rab1 associates specifically with immature secretory granules and drives granule growth. In addition to their roles in granule growth, both Rab1 and Rab11 appear to have additional roles during exocytosis; Rab11 function is necessary for exocytosis, while the presence of Rab1 on immature granules may prevent precocious exocytosis. Overall, these results highlight a new and unexpected role for Rab GTPases in secretory granule maturation.

cell biology↗

bioRxiv2020

Mistargeting of secretory cargo in retromer-deficient cells

ABSTRACTIntracellular trafficking is a basic and essential cellular function required for delivery of proteins to the appropriate subcellular destination; this process is especially demanding in professional secretory cells, which synthesize and secrete massive quantities of cargo proteins via regulated exocytosis. The Drosophila larval salivary glands are professional secretory cells that synthesize and secrete mucin proteins at the onset of metamorphosis. Using the larval salivary glands as a model system, we have identified a role for the highly conserved retromer complex in trafficking of secretory granule membrane proteins. We demonstrate that retromer-dependent trafficking via endosomal tubules is induced at the onset of secretory granule biogenesis, and that recycling via endosomal tubules is required for delivery of essential secretory granule membrane proteins to nascent granules. Without retromer function, nascent granules do not contain the proper membrane proteins; as a result, cargo from these defective granules is mistargeted to Rab7-positive endosomes, where it progressively accumulates to generate dramatically enlarged endosomes. Retromer complex dysfunction is strongly associated with Alzheimer’s disease, characterized by accumulation of amyloid β (Aβ). We show that amyloid precursor protein (APP) undergoes regulated exocytosis and accumulates within enlarged endosomes in retromer-deficient cells. These results highlight recycling of secretory granule membrane proteins as a critical step during secretory granule maturation and provide new insights into our understanding of retromer complex function in secretory cells. Our data also suggests that misrouting of secretory cargo, including APP, may contribute to the progressive nature of neurodegenerative disease.SUMMARY STATEMENT Retromer complex dysfunction is implicated in neurodegeneration. Here the authors show a new role for the retromer complex in recycling of secretory membrane and cargo proteins during regulated exocytosis.View Full Text

developmental biology↗