EDITORIAL
The conundrum of oxidant-induced barrier dysfunction

Arnold Johnson

The Lung Biology Laboratory, Upstate New York Veterans Affairs Healthcare Stratton Medical Center, Albany, New York 12208, American Journal of Physiology-, Lung Cellular and Molecular Physiology, September 2000, Volume 279 (23)


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IN THIS ISSUE of the American Journal of Physiology-Lung Cellular and Molecular Physiology, Shi et al. (7) have shown that activation of p60c-Src mediates the diperoxovanadate (DPV)-induced increase in endothelial permeability of bovine pulmonary arterial endothelial cells. DPV, which is produced by the reaction of equimolar amounts of orthovanadate and hydrogen peroxide (H2O2), has the unique ability to both activate tyrosine kinases and inhibit protein tyrosine phosphatases. DPV is used as a model for H2O2-induced activation of tyrosine kinase activity and barrier dysfunction (10). The conclusions of Shi et al. (7) are based on their data indicating that the c-Src inhibitors genistein and PP-2 and overexpression of a dominant negative plasmid for p60c-Src attenuate the DPV-induced increases in albumin clearance and/or decrease in electrical resistance. Importantly, tyrosine phosphorylation, autophosphorylation, and peptide phosphorylation assays were used to substantiate the noted changes in tyrosine kinase activity. A most novel finding of this paper is an increase in p60c-Src-associated cortactin and myosin light chain kinase (MLCK) immunoactivity in response to DPV. These findings substantiate their previous findings (5, 10) and those of others (2, 3, 9) noting that in response to reactive oxygen species (ROS), the endothelial cell is not simply the victim of nonspecific mediated reactions such as an oxidation attack on membranes followed by the loss of membrane integrity and necrosis. Indeed, as exemplified in this paper (7), the endothelium responds in a orchestrated series of intracellular reactions characterized by activation of c-Src with phosphorylation of cortactin and MLCK, resulting in a decrease in barrier selectivity to albumin.

A caveat for the previous work in this field (2, 6, 8) is the selectivity of the pharmacological probes that are used to alter the activity of kinases such as genistein for c-Src and, in the case of our own work, calphostin C for protein kinase C-alpha . Thus an important aspect of the study by Shi et al. (7) is the verification of the role of p60c-Src in barrier function. They showed that expression of constitutively active and wild-type p60c-Src increased the response to DPV (i.e., a further decrease in the electrical resistance), whereas expression of a dominant negative mutant p60c-Src decreased the response to DPV (i.e., increased the electrical resistance). Notwithstanding the intricate "cross-talk network" in signal transduction, this paper notably acclaims a specific role for p60c-Src in regulating barrier function.

In the paper by Shi et al. (7), the increased association of phosphorylated cortactin and MLCK with p60c-Src is noted in pulmonary arterial endothelial cells. Yet, it is worth documenting these events in endothelial cells derived from the microcirculation because there may be DPV- and ROS-induced responses that are different between endothelial cells derived from large and small vessels (4). These needed studies are underscored by the large surface area available for fluid exchange that occurs in the lung microcirculation. In addition, what is the role of tyrosine phosphorylated cortactin and MLCK in barrier dysfunction in response to tyrosine kinase activation and ROS? With today's technology, expression of mutant inactive MLCK and cortactin that contain critical sites unavailable for phosphorylation or, conversely, expression of a constitutively active endothelial MLCK can yield much needed information. Interestingly, the data by Shi et al. (7) indicate that p60c-Src only partially mediates the effect of DPV. Obviously, all the members of the signal transduction orchestra have not been identified, and we need more investigation of the response to tyrosine kinase activation and ROS. Apparently, other possible signals would be those hosted by other kinases as Ferro et al. (1) demonstrated for protein kinase C-alpha or as Shi et al. (7) mentioned for the activity of mitogen-activated protein kinase and the phospholipase D-phosphatidic acid pathway. Thus as we are all aware and as exemplified in the important work of Shi et al., "Science is the knowledge of consequences, and dependence of one fact upon another" (Thomas Hobbes, English philosopher and author, 1588-1679).


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1.   Ferro, T, Clements R, Neumann P, Gertzberg N, and Johnson A. Protein kinase C-alpha mediates endothelial barrier dysfunction induced by TNF-alpha . Am J Physiol Lung Cell Mol Physiol 278: L1107-L1117, 2000[Abstract/Free Full Text].

2.   Johnson, A, Phillips P, Hocking D, Tsan MF, and Ferro TJ. A protein kinase inhibitor prevents pulmonary edema in response to H2O2. Am J Physiol Heart Circ Physiol 257: H1012-H1022, 1989.

3.   Lopez-Ongil, S, Torrecillas G, Perez-Sala D, Gonzalez-Santiago L, Rodriguez-Puyol M, and Rodriguez-Puyol D. Mechanisms involved in the contraction of endothelial cells by hydrogen peroxide. Free Radic Biol Med 26: 501-510, 1999[ISI][Medline].

4.   Lum, H, and Malik AB. Regulation of vascular endothelial barrier function. Am J Physiol Lung Cell Mol Physiol 267: L223-L241, 1994[Abstract/Free Full Text].

5.   Natarajan, V, Vepa S, Shamlal R, Al-Hassani M, Ramasarma T, Ravishanker HN, and Scribner WM. Tyrosine kinases and calcium dependent activation of endothelial cell phospholipase D by diperoxovanadate. Mol Cell Biochem 183: 113-124, 1998[ISI][Medline].

6.   Serfilippi, G, Ferro TJ, and Johnson A. The activation of protein kinase C mediates the alteration in pulmonary vasoreactivity induced by tumor necrosis factor-alpha . Am J Physiol Lung Cell Mol Physiol 267: L282-L290, 1994[Abstract/Free Full Text].

7.   Shi, S, Garcia JGN, Roy S, Parinandi NL, and Natarajan V. Involvement of c-Src in diperoxovanadate-induced endothelial cell barrier dysfunction. Am J Physiol Lung Cell Mol Physiol 279: L441-L451, 2000[Abstract/Free Full Text].

8.   Shi, S, Verin AD, Schaphorst KL, Gilbert-McClain LL, Patterson CE, Irwin R, Natarajan V, and Garcia JGN Role of tyrosine phosphorylation in thrombin-induced endothelial cell contraction and barrier function. Endothelium 6: 158-171, 1998.

9.   Siflinger-Birnboim, A, Schnitzer JE, Del Vecchio PJ, and Malik AB. Activation of protein kinase C pathway contributes to hydrogen peroxide-induced increase in endothelial permeability. Lab Invest 67: 24-30, 1992[ISI][Medline].

10.   Vepa, S, Scribner WM, Parinandi NL, English D, Garcia JGN, and Natarajan V. Hydrogen peroxide stimulates tyrosine phosphorylation of focal adhesion kinase in vascular endothelial cells. Am J Physiol Lung Cell Mol Physiol 277: L150-L158, 1999[Abstract/Free Full Text].


Am J Physiol Lung Cell Mol Physiol 279(3):L439-L440
1040-0605/00 $5.00 Copyright © 2000 the American Physiological Society




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