Endocytosis and Secretion

All cells of the liver and pancreas secrete nascent proteins into the extracellular space to maintain normal organ function, while internalizing scores of different trophic growth factors, receptors and pathogens. The lab's goal is to understand the mechanistic basis of these important processes in healthy and diseased cells.

  • Association of a dynamin-like protein with the Golgi in mammalian cells

  • Actin and Arf1-dependent recruitment of a cortactin–Dyn2 complex to the Golgi regulates post-Golgi transport

  • Waves sequester and internalize EGFR

  • Cortactin is a component of clathrin-coated pits and participates in RME

  • EGF-induced phosphorylation of caveolin 1 stimulates caveolae formation

View the publications below to learn more about the lab's work.

CIN85 phosphorylation is essential for EGFR ubiquitination and sorting into multivesicular bodies.

Molecular Biology of the Cell. 2012;23:3602.

CIN85 phosphorylation is essential for EGFR ubiquitination and sorting into MVBs

Barbara Schroeder, Subhashini Srivatsan, Andrey Shaw, Daniel Billadeau, Mark A. McNiven

Ubiquitination of the epidermal growth factor receptor (EGFR) by cbl and its cognate adaptor cbl-interacting protein of 85 kDa (CIN85) is known to play an essential role in directing this receptor to the lysosome for degradation. These findings provide novel insights into how src-kinase-based regulation of a cbl adaptor regulates the fate of the EGFR.

Read more.

Hepatocytes internalize trophic receptors at large endocytic 'hot spots.'

Hepatology. 2011;54:1819.

Hong Cao, Eugene W. Krueger, Mark A. McNiven

Clathrin-mediated endocytosis in mammalian epithelial cells is believed to require the synergistic action of structural coat proteins and mechanochemical enzymes to deform and sever the plasma membrane (PM) into discreet vesicles. These findings suggest that hepatocytes sequester or prerecruit both structural and enzymatic components of the clathrin-based endocytic machinery to functional hot spots, from which large numbers of coated pits form and vesicles are generated. This process may mimic the endocytic organization found at the synapse in neuronal cells.

Read more.

Recycling of the epidermal growth factor receptor is mediated by a novel form of the clathrin adaptor protein Eps15.

The Journal of Biological Chemistry. 2011;286:35196.

Susan Chi, Hong Cao, Yu Wang, Mark A. McNiven

Sorting of epidermal growth factor receptor (EGFR) is tightly regulated by the endocytic machinery. EGFR pathway substrate 15 (Eps15) is an endocytic adaptor protein. A novel form of Eps15, Eps15S regulates EGFR recycling and function of the ERC. This finding suggests that distinct forms of Eps15 can function differentially in EGFR trafficking.

Read more.

A Dyn2-CIN85 complex mediates degradative traffic of the EGFR by regulation of late endosomal budding.

A Dyn2-CIN85 complex mediates degradative traffic of the EGFR by regulation of late endosomal budding

The EMBO Journal. 2010;29:3039.

Barbara Schroeder, Shaun G. Weller, Jing Chen, Daniel Billadeau, Mark A. McNiven

The epidermal growth factor receptor (EGFR) is overexpressed in a variety of human cancers. Findings provide novel insights into a previously unknown protein complex that can regulate EGFR traffic at very late stages of the endocytic pathway.

Read more.

Src-mediated phosphorylation of dynamin and cortactin regulates the "constitutive" endocytosis of transferrin.

Src-mediated phosphorylation of dynamin and cortactin regulates the "constitutive" endocytosis of transferrin.

Molecular Biology of the Cell. 2010;30:781.

Hong Cao, Jing Chen, Eugene W. Krueger, Mark A. McNiven

Endocytosis of the transferrin receptor is a regulated process that requires activated src kinase and, subsequently, phosphorylation of two important components of the endocytic machinery: the large GTPase dynamin 2 (Dyn2) and its associated actin-binding protein, cortactin. To our knowledge these findings are among the first to implicate an src-mediated endocytic cascade in what was previously presumed to be a nonregulated internalization process.

Read more.

Src kinase regulates the integrity and function of the Golgi apparatus via activation of dynamin 2

Src kinase regulates the integrity and function of the Golgi apparatus via activation of dynamin 2

PNAS. 2010;107(13):5863.

Shaun G. Weller, Mirco Capitani, Hong Cao, Massimo Micaroni, Alberto Luini, Michele Sallese, Mark A. McNiven

C-Src has profound effects on Golgi structure. GTPase dynamin (Dyn2) has been implicated in Golgi vesiculation during secretion. Inhibiting Dyn2 activity could attenuate active src-induced Golgi fragmentation. We found that activation of Dyn2 by src kinase regulates Golgi integrity and vesiculation during the secretory process.

Read more.

Dynamin 2 mediates fluid-phase micropinocytosis in epithelial cells

Journal of Cell Science. 2007;120:4167.

Hong Cao, Jing Chen, Muyiwa Awoniyi, John R. Henley, Mark A. McNiven

It is well-known that dynamin 2 (Dyn2) participates in clathrin- and caveolae-mediated endocytosis; however, the role of Dyn2 in coat-independent endocytic processes remains controversial. Here we demonstrate a role for specific spliced variants of Dyn2 in the micropinocytosis of fluid in epithelial cells, independent of coat-mediated endocytic pathways. These findings suggest that Dyn2 function is required for the coat-independent internalization of fluid through endocytic pathways distinct from macropinocytosis and, in addition, implicate different Dyn2 spliced variants in specific endocytic functions.

Read more.

A novel endocytic mechanism of epidermal growth factor receptor sequestration and internalization

Cancer Research. 2006;66(7):3603.

James D. Orth, Eugene W. Krueger, Shaun G. Weller, Mark A. McNiven

Cells form transient, circular dorsal ruffles or "waves" in response to stimulation of receptor tyrosine kinases, including epidermal growth factor receptor (EGFR) or platelet-derived growth factor receptor. These findings characterize a structure that selectively sequesters large numbers of activated EGFR for their subsequent internalization, independent of traditional endocytic mechanisms such as clathrin pits or caveolae.

Read more.

Epithelial growth factor-induced phosphorylation of caveolin 1 at tyrosine 14 stimulates caveolae formation in epithelial cells

Journal of Biological Chemistry. 2006;281(8):4570.

Lidiya Orlichenko, Bing Huang, Eugene Krueger, Mark A. McNiven

Caveolae are flask-shaped endocytic structures composed primarily of caveolin-1 (Cav1) and caveolin-2 (Cav2) proteins. This study provides novel insights into how cells regulate caveolae formation and implicates EGF-based signaling cascades in the phosphorylation of Cav1 as a stimulus for caveolae assembly.

Read more.

Caveolin-1 interacts directly with dynamin 2

Caveolin-1 interacts directly with dynamin 2

Journal of Molecular Biology. 2005;348:491.

Qing Yao, Jing Chen, Hong Cao, James D. Orth, J. Michael McCaffery, Radu-Virgil Stan, Mark A. McNiven

Caveolin is the principal component of caveolae in vivo. In addition to a structural role, it is believed to play a scaffolding function to organize and inactivate signaling molecules that are concentrated on the cytoplasmic surface of caveolar membranes. These studies provide the first evidence for a direct interaction between dynamin and the caveolin coat, and demonstrate a selectivity of one Dyn2 form toward the caveolae-mediated endocytosis.

Read more.