John G. Forte

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Research Interests

General interests of the laboratory concern the mechanisms of biological membrane transport and the regulation of these processes. Specific areas of research emphasis include: regulated membrane trafficking and sorting associated with secretion; recruitment and recycling of membrane transport proteins; role of cytoskeletal proteins in membrane flow and turnover; protein phosphorylation associated with stimulus-secretion coupling; structural and functional characterization of intrinsic membrane transport proteins.

Current Projects

Parietal cell activation represents one of the most dramatic models in which to study apical membrane remodeling associated with regulated secretion. Stimulation of these cells, in culture as in vivo, involves massive redistribution of membranes and transport enzymes from cytoplasmic vesicles to the apical plasma membrane domain. We have the means to monitor these changes structurally, biochemically and functionally. These techniques, as well as immunocytochemical probes of cytoskeletal proteins, are used to define the nature of membrane-cytoskeletal interactions that direct membrane movements to and from the cell surface. The sites, specificities, and mechanisms of the fusion reactions underlying these events of membrane recruitment are also being studied.

A second major project examines the role of protein phosphorylation in the cell activation cascade. Using the gastric acid-secreting parietal cell as a model system, we have correlated several phosphoproteins with cellular activation via cyclic AMP-mediated PKA. We now seek to establish the direct functional role of these phosphoproteins in the trafficking and recruitment of membrane transporters from a conserved inactive cytoplasmic membrane pool to the apical plasmalemma.

Another project evaluates structure-function relationships within the class of cation-tranporting P-type ATPases. We contrast two heterodimeric pump enzymes, the Na,K-ATPase, and its trafficking and functional activity at the basolateral membrane, with the H,K-ATPase, which is trafficked exclusively to the apical membrane. These proteins are studied in vitro, where conditions of interaction can be manipulated, in cell culture where variants in subunits may be expressed, and in situ where the real physiological pathways can be monitored.

Selected Publications

A possible mechanism for ezrin to establish epithelial cell polarity.  [Zhu L, Crothers J Jr, Zhou R, Forte JG (2010) Am J Physiol, Cell Physiol. 299(2):C431-43]

Apical recycling of the gastric parietal cell H,K-ATPase.  [Forte JG, Zhu L (2010) Annu Rev Physiol. 72:273-96]

Novel insights of the gastric gland organization revealed by chief cell specific expression of moesin.  [Zhu L, Hatakeyama J, Zhang B, Makdisi J, Ender C, Forte JG (2009) Am J Physiol Gastrointest Liver Physiol. 296(2):G185-95]

Comparative study of ezrin phosphorylation among different tissues: more is good; too much is bad.  [Zhu L, Hatakeyama J, Chen C, Shastri A, Poon K, Forte JG (2008) Am J Physiol Cell Physiol. 295(1):C192-202]

The conformation of H,K-ATPase determines the nucleoside triphosphate (NTP) selectivity for active proton transport.  [Reenstra WW, Crothers J Jr, Forte JG  (2007) Biochemistry46(35):10145-52]

High turnover of ezrin T567 phosphorylation: conformation, activity and cellular function. [Zhu L, Zhou R, Mettler S, Wu T, Abbas A, Delaney J, Forte JG. (2007) Am J Physiol Cell Physiol.  293(3):C874-84]

Modulatory role of phosphoinositide 3-kinase (PI3K) in gastric acid secretion.  [Mettler SE, Ghayouri S, Christensen GP, Forte JG.  (2007) Am J Physiol Gastrointest Liver Physiol.  293(3):G532-43]

Phosphorylation of ezrin on threonine 567 produces a change in secretory phenotype and repolarizes the gastric parietal cell. [Zhou R, Zhu L, Kodani A, Hauser P, Yao X, Forte JG (2005) J Cell Science 118(19): 4381-4391]

Cellular localization and stimulation-associated distribution dynamics of syntaxin-1 and syntaxin-3 in gastric parietal cells.  [Karvar S, Zhu L, Crothers J Jr, Wong W, Turkoz M, Forte JG (2005)Traffic 6(8):654-66]

Ezrin oligomers are the membrane-bound dormant form in gastric parietal cells.  [Zhu L, Liu Y, Forte JG (2005) Am J Physiol Cell Physiol. 288(6):C1242-54]

Membrane fusion correlates with surface charge in exocytic vesicles.  [Duman JG, Lee E, Lee GY, Singh G, Forte JG  (2004) Biochemistry. 43(24):7924-39]

What is the role of SNARE proteins in membrane fusion? [Duman JG and Forte JG (2003) Am. J. Physiol Cell Physiol. 285:C237-49]

Cell biology of acid secretion by the parietal cell. [Yao X and Forte JG (2003) Ann Rev Physiol. 65:103-31]

Localization and function of snap-25 and vamp-2 in functioning gastric parietal cells. [Karvar S, Yao X, Crothers JM Jr., Liu Y, Forte JG (2002) J. Biol. Chem. 277(51):50030-5, 2002]

Three-dimensional reconstruction of cytoplasmic membrane networks in parietal cells. [Duman JG, Pathak NJ, Ladinsky MS, McDonald KL, Forte JG (2002) J. Cell Science, 115(6):1251-125]

Ca²⁺ and Mg²⁺/ATP independently trigger homotypic membrane fusion in gastric secretory membrane. [Duman JG, Singh G, Lee GY, Machen TE, Forte JG (2002) Traffic, 3(3):203-217]

Gastric H,K-ATPase and acid-resistant surface proteins. [Thangarajah H, Wong A, Chow D-C, Crothers JM Jr, Forte JG (2002) Am J Physiol Gastrointest & Liver. 282:G953-G961]

Syntaxin 3 is required for cAMP-induced acid secretion: The streptolysin O permeabilized gastric gland model. [Ammar DA, Zhou R, Forte JG, Yao X (2002) Am J Physiol Gastrointest & Liver. 282:G23-G33]

Vesicular trafficking machinery, the actin cytoskeleton, and H⁺-K⁺-ATPase recycling in the gastric parietal cell. [Okamoto CT and Forte FG (2001) J Physiol. 532(Pt 2):287-96]

Last Updated 2010-08-19