Tumor Cell Growth and Membrane Trafficking

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. Dr. McNiven's lab's focus is to understand the mechanistic basis of these important processes in healthy and diseased cells.

These publications describe the Cytoskeletal Membrane Dynamics Lab's work in tumor cell growth and membrane trafficking:

Inhibition of c-Abl directs the TfR to the lysosome for degradation (figure 6).

  • Cao H, Schroeder B, Chen J, Schott MB, McNiven MA. The endocytic fate of the transferrin receptor is regulated by c-Abl kinase. The Journal of Biological Chemistry. 2016;291:16424.

    Clathrin-mediated endocytosis of transferrin (Tf) and its cognate receptor (TfR1) is a central pathway supporting the uptake of trophic iron. It has generally been assumed that this is a constitutive process. However, we have reported that the non-receptor tyrosine kinase, Src, is activated by Tf to facilitate the internalization of the Tf-TfR1 ligand-receptor complex. As an extension of these findings, we have tested whether subsequent trafficking steps might be regulated by additional kinase-dependent cascades, and we observed a significant endocytic block by inhibiting c-Abl kinase by a variety of methods. Importantly, Tf internalization was reduced significantly in all of these cell models and could be restored by re-expression of WT c-Abl.

    Surprisingly, this attenuated Tf-TfR1 endocytosis was due to a substantial drop in both the surface and total cellular receptor levels. Importantly, inhibition of c-Abl resulted in a striking redistribution of the chaperone Hsc70 from a diffuse cytosolic localization to an association with the TfR1 at the late endosome-lysosome. Thus, inhibition of c-Abl minimizes receptor recycling pathways and results in chaperone-dependent trafficking of the TfR1 to the lysosome for degradation.

The formation of membranous tubules extending from MVBs and autophagosomes in HBV-expressing cells is dependent upon Rab7 and facilitates fusion with the lysosome (figure 3).

  • Inoue J, Krueger EW, Chen J, Cao H, Ninomiya M, McNiven MA. HBV secretion is regulated through the activation of endocytic and autophagic compartments mediated by Rab7 stimulation. Journal of Cell Science. 2015; 128:1696.

    HBV-induced activation of the GTPase Rab7 causes tubule formation from MVBs and autophagic compartments, which alters secretion of HBV particles from the cell. The activation of Rab7 is caused mainly by the pre core protein, which is a precursor of HBeAg. Finally, siRNA against Rab7 increases secretion of HBV particles as they are no longer trafficked to the lysosome.

    Rab7 expression is key for hepatocytes to form long tubules from the endosomes believed to contribute to infection.

From figure 6

  • Eppinga RD, Krueger EW, Weller SG, Zhang L, Cao H, McNiven MA. Increased expression of the large GTPase dynamin 2 potentiates metastatic migration and invasion of pancreatic ductal carcinoma. Oncogene. 2012; 31:1228.

    Src-mediated tyrosine kinase signaling pathways promote pancreatic ductal adenocarcinoma (PDAC) metastasis, though the molecular mechanisms supporting this invasive process are poorly understood and represent important and novel therapeutic targets.

    The goal of this study was to test if large GTPase dynamin 2 (Dyn2), an Src-kinase substrate, is upregulated in human pancreatic tumors and to define its role in cell migration and metastatic invasion using in vitro assays and nude mouse models. Findings are the first to implicate dynamin in any neoplastic condition and to directly demonstrate a role for this mechanoenzyme in invasive cell migration.

From figure 5

  • Wang Y, McNiven MA. Invasive matrix degradation at focal adhesions occurs via protease recruitment by a FAK-p130Cas complex. The Journal of Cell Biology. 2012;196:375.

    Tumor cell migration and the concomitant degradation of extracellular matrix (ECM) are two essential steps in the metastatic process. It is well-established that focal adhesions (FAs) play an important role in regulating migration; however, whether these structures contribute to matrix degradation is not clear. In this study, we report that multiple cancer cell lines display degradation of ECM at FA sites that requires the targeted action of MT1-MMP. These findings demonstrate a novel function for FAs and also provide molecular insights into MT1-MMP targeting and function.

From figure 5

From figure 4

  • Kruchten AE, Krueger EW, Wang Y, McNiven MA. Distinct phospho-forms of cortactin differentially regulate actin polymerization and focal adhesions. American Journal of Physiology: Cell Physiology. 2008;295:C1113.

    Cortactin is an actin-binding protein that is overexpressed in many cancers and is a substrate for both tyrosine and serine/threonine kinases. Findings provide novel insights into how distinct phospho-forms of cortactin may differentially contribute to actin and focal adhesion dynamics to control cell migration.

Dynamin 2 binds γ-tubulin and participates in centrosome cohesion.

  • Thompson HM, Cao H, Chen J, Euteneuer U, McNiven MA. Dynamin 2 binds γ-tubulin and participates in centrosome cohesion. Nature Cell Biology. 2004;6:335.

    Dynamin 2 (Dyn2) is a large GTPase involved in vesicle formation and actin reorganization1-3. In this study, we report a novel role for Dyn2 as a component of the centrosome that is involved in centrosome cohesion. These findings suggest a novel function for Dyn2 as a participant in centrosome cohesion.

A dynamin-cortactin-arp2/3 complex mediates actin reorganization in growth factor-stimulated cells.

  • Krueger EW, Orth JD, Cao H, McNiven MA. A dynamin-cortactin-arp2/3 complex mediates actin reorganization in growth factor-stimulated cells. Molecular Biology of the Cell. 2003; 14:1085.

    The mechanisms by which mammalian cells remodel the actin cytoskeleton in response to motogenic stimuli are complex and a topic of intense study. Dynamin 2 (Dyn2) is a large GTPase that interacts directly with several actin-binding proteins, including cortactin. Findings demonstrate that cortactin and Dyn2 function together in a supramolecular complex that assembles in response to growth factor stimulation and mediates the remodeling of actin to facilitate lamellipodial protrusion at the leading edge of migrating cells.

The large GTPase dynamin regulates actin comet formation and movement in living cells.

  • Orth JD, Krueger EW, Cao H, McNiven MA. The large GTPase dynamin regulates actin comet formation and movement in living cells. PNAS. 2001;99:167.

    The large GTPase dynamin (Dyn2) has been demonstrated by us and others to interact with several different actin-binding proteins. To define how Dyn2 might participate in actin dynamics in livings cells, we have expressed green fluorescent protein (GFP)-tagged Dyn2 in cultured cells and observed labeling of comet-like vesicles and macropinosomes. These findings demonstrate a role for Dyn2 in actin-based vesicle motility.

Regulated interactions between dynamin and the actin-binding protein cortactin modulate cell shape.

  • McNiven MA, Kim L, Krueger EW, Orth JD, Cao H, Wong TW. Regulated interactions between dynamin and the actin-binding protein cortactin modulate cell shape. Journal of Cell Biology. 2000;151:187.

    The dynamin family of large GTPases has been implicated in the formation of nascent vesicles in both the endocytic and secretory pathways. It is believed that dynamin interacts with a variety of cellular proteins to constrict membranes. The actin cytoskeleton has also been implicated in altering membrane shape and form during cell migration, endocytosis and secretion and has been postulated to work synergistically with dynamin and coat proteins in several of these important processes. Findings provide the first demonstration that dynamin can interact with the actin cytoskeleton to regulate actin reorganization and subsequently cell shape.