Biology subjects

Heit, B.

Publications and source records attributed to Heit, B..

3 recordsLinked to original sources

bioRxiv2018

PACS-1 and Adaptor Protein-1 Mediate ACTH Trafficking to the Regulated Secretory Pathway

The regulated secretory pathway is a specialized form of protein secretion found in endocrine and neuroendocrine cell types. Pro-opiomelanocortin (POMC) is a pro-hormone that utilizes this pathway to be trafficked to dense core secretory granules (DCSGs). Within this organelle, POMC is processed to multiple bioactive hormones that play key roles in cellular physiology. However, the complete set of cellular membrane trafficking proteins that mediate the correct sorting of POMC to DCSGs remain unknown. Here, we report the roles of the phosphofurin acidic cluster sorting protein - 1 (PACS-1) and the clathrin adaptor protein 1 (AP-1) in the targeting of POMC to DCSGs. Upon knockdown of PACS-1 and AP-1, POMC is readily secreted into the extracellular milieu and fails to be targeted to DCSGs.

cell biology↗

bioRxiv2018

Soluble CD93 is an Apoptotic Cell Opsonin Recognized by the αxβ2 Integrin

AO_SCPLOWBSTRACTC_SCPLOWEfferocytosis - the phagocytic removal of apoptotic cells - is essential for the maintenance of homeostasis and prevention of the inflammatory and autoimmune diseases which can follow the lysis of uncleared apoptotic cells. CD93 is a transmembrane glycoprotein previously implicated in efferocytosis and angiogenesis, and upon mutation, results in the onset of efferocytosis-associated diseases such as atherosclerosis and rheumatoid arthritis. CD93 is produced as a cell surface protein which is shed as soluble CD93, but it is unknown how CD93 mediates efferocytosis or whether its efferocytic activity is mediated by the soluble or membrane-bound form. Herein, we demonstrate that the membrane bound form of CD93 has no phagocytic, efferocytic, or tethering activity, whereas soluble CD93 potently opsonizes apoptotic cells but not a broad range of Gram-Negative, Gram-Positive or fungal microorganisms. Using mass spectrometry, we identified the x{beta}2 integrin as the receptor required for soluble CD93-mediated efferocytosis, and via deletion mutagenesis determined that soluble CD93 binds to apoptotic cells via its C-Type Lectin-Like domain, and to x{beta}2 by its EGF-like repeats. This bridging of apoptotic cells to the x{beta}2 integrin markedly enhanced efferocytosis by macrophages, and could be abrogated by knockdown of x{beta}2 integrin. Combined, these data elucidate the mechanism by which CD93 regulates efferocytosis and identify a previously unreported opsonin-receptor system utilized by the immune system for the efferocytic clearance of apoptotic cells.

immunology↗

bioRxiv2017

Membrane Diffusion Occurs by a Continuous-Time Random Walk Sustained by Vesicular Trafficking.

Diffusion in cellular membranes is regulated by processes which occur over a range of spatial and temporal scales. These processes include membrane fluidity, inter-protein and inter-lipid interactions, interactions with membrane microdomains, interactions with the underlying cytoskeleton, and cellular processes which result in net membrane movement. The complex, non-Brownian diffusion that results from these processes has been difficult to characterize, and moreover, the impact of factors such as membrane recycling on membrane diffusion remains largely unexplored. We have used a careful statistical analysis of single-particle tracking data of the single-pass plasma membrane protein CD93 to show that the diffusion of this protein is well-described by a continuous-time random walk in parallel with an aging process mediated by membrane corrals. The overall result is an evolution in the diffusion of CD93: proteins initially diffuse freely on the cell surface, but over time, become increasingly trapped within diffusion-limiting membrane corrals. Stable populations of freely diffusing and corralled CD93 are maintained by an endocytic/exocytic process in which corralled CD93 is selectively endocytosed, while freely diffusing CD93 is replenished by exocytosis of newly synthesized and recycled CD93. This trafficking not only maintained CD93 diffusivity, but also maintained the heterogeneous distribution of CD93 in the plasma membrane. These results provide insight into the nature of the biological and biophysical processes that can lead to significantly non-Brownian diffusion of membrane proteins, and demonstrate that ongoing membrane recycling is critical to maintaining steady-state diffusion and distribution of proteins in the plasma membrane.

biophysics↗