Vivian W Tang
Research Assistant Professor of Cell and Developmental Biology
Cell-Cell Interactions, Cytoskeleton
B.A., University of California, Berkeley (Physiology)
Ph.D., University of California, San Francisco (Physiology)
Postdoc, Harvard Medical School, Harvard University
Cell-Cell interactions in Health and Disease
Regulation of cell-cell adhesions in kidney diseases
Focal and segmental glomerulosclerosis (FSGS) is a common cause of nephrotic syndrome, which accounts for up to 20% of cases in children and 40% of cases in adult. FSGS is characterized by proteinuria with high incidence of development to end-stage renal failure. Injury to or inherent within the kidney glomerular podocyte constitutes the critical event leading to FSGS. There is no specific treatment for FSGS due to the complexity of its etiology. Short of transplantation, preventing further injury to podocytes and preserving the slit diaphragm permeability barrier is key to decreasing the rate of disease progression. FSGS-associated proteinuria is primarily handled by controlling blood pressure and the administration of immunosuppressive agents. However, the potential cumulative toxicity of the various agents used for managing the disease can be as bad or worse than the disease, making FSGS one of the most difficult renal diseases to manage.
The mechanism leading to proteinuria and gross cellular damage in FSGS is not understood. Genetic linkage studies have identified several slit diaphragm proteins in the development of FSGS, including actin-regulators and cell-cell adhesion molecules. Transgenic knockout mouse models further support the roles of actin regulators and cell-cell adhesion proteins in the pathogenesis of proteinuria and FSGS. In addition, drugs that retard the progression or recurrence of FSGS can stabilize the actin cytoskeleton, suggesting that disrupting actin dynamics could be a convergent pathway to the development of FSGS.
The actin cytoskeleton participates in cell-cell adhesion and maintenance of the slit diaphragm filtration barrier in many fundamental ways. Actin organizes plasma membrane domains by clustering membrane adhesion molecules. In addition, it provides anchorage of cell-cell adhesion molecules to the underlying cytoplasmic actin network. Moreover, actin participates in mechanotransduction at sites of cell-cell adhesion and in the cytoplasm to allow adaptation to changes in glomerular pressure during health and disease. Ultimately, the actin cytoskeleton determines the validity of the glomerular filtration barrier provided by the slit diaphragm.
Given the complexity of the slit diaphragm, dissecting the structure-function relationships of its molecular components is essential to revealing the mechanism behind development of proteinuria and FSGS. The slit diaphragm is a modified adherens junction, which can be divided into three functional modules (Fig. 1a): a membrane adhesion complex (MAC) formed by transmembrane cell-cell adhesion molecules. MAC is attached to the actin cytoskeleton (Fig. 1b) via a cytoplasmic receptor complex (CRC) and a junction-actin regulatory complex (JARC). FSGS1/α-actinin-4 is recruited to the CRC to support actin assembly through a nucleation mechanism that requires the arp2/3 nucleation complex (Arp). The exact molecular nature of these modules is unclear and is the focus of our current research.
Figure 1. The slit diaphragm/adherens junction is divided into three functional modules: membrane adhesion complex (MAC), cytoplasmic receptor complex (CRC), and the junction-actin regulatory complex (JARC). (a) Addition of actin monomers to the membrane results in actin assembly promoted by the arp2/3 nucleation promoter complex (Arp). (b) Electron micrograph showing actin filaments (orange arrow) assembled on purified membrane extracted with CHAPS detergent.
Research Career Award, NIDDK, NIH
Tang, V. (2017) Cell-cell adhesion interface: rise of the lateral membrane. REVIEW
Kannan, N. and V. W. Tang (2015) Synaptopodin couples epithelial contractility to α-actinin-4–dependent junction maturation. J. Cell Biol. 211:407-434. ABSTRACT
Tang, V. W. and W. M. Brieher. (2013) Capping actin barbed-ends by FSGS3/CD2AP stabilizes actin at the adherens junction to strengthen epithelial cohesion and protect permeability barrier. J. Cell Biol. 203:815-833. ABSTRACT
Tang, V. W. and W. M. Brieher. (2012) Alpha-actinin-4/FSGS1 is required for arp2/3-dependent actin assembly at the adherens junction. J. Cell Biol. 196:115-130. ABSTRACT
Tang, V. W. (2006) Proteomics and bioinformatic analysis of tight junction reveals an unexpected cluster of synaptic proteins. Biology Direct 1:37. ABSTRACT
Tang, V. W. and D. A. Goodenough. (2003) Paracellular ion channel at the tight junction. Biophys J. 84(3):1660-73. ABSTRACT
Tang, V. W.(aka Wong, V. W.) and D. A. Goodenough. Paracellular channels. (1999) Science 285(5424):62. ABSTRACT
Tang, V. W.(aka Wong, V. W.), Ching, D., McCrea, P.D., and G.L. Firestone. (1999) Glucocorticoid down regulation of fascin protein expression is required for the steriod-induced formation of tight junctions and cell-cell interactions in rat mammary epithelial tumor cells. J. Biol. Chem. 274(9):5443-5453. ABSTRACT
Tang, V. W.(aka Wong, V. W.), and Gumbiner, B.M. (1997) A synthetic peptide corresponding to the extracellular domain of occludin perturbs the tight junction permeability barrier. J. Cell Biol. 136:399-409. ABSTRACT
Tang, V. W.(aka Wong, V. W.), (1997) Phosphorylation of occludin correlates with occludin localization and function at the tight junction. Am. J. Physiol. 42(6):1859-1867. ABSTRACT