Cellular Biochemistry 

We are studying endothelin- and stress-mediated signal transduction in the adult ventricular myocardium. Cardiac hypertrophy, a major cause of heart diseases such as myocardial infarction and cardiac arrhythmias, occurs when the heart is continuously exposed to increased load and/or neurohormonal factors.

Certain paracrine transmitters, such as endothelin, angiotensin II, and lpha1-adrenergic agonists, produce both positive inotropic and hypertrophic effects on the heart. These agonists stimulate the production of diacylglycerol. Diacylglycerol then activates specific isoenzymes of the protein kinase C (PKC) family which translocate to, and catalyze the phosphorylation of subcellular targets. One of the targets activated by PKC is a Mitogen-Activated Protein (MAP) kinase cascade which results in the activation of both p42mapk and p44mapk. The p38mapk pathway is also activated in resonse to hypertrophic stimuli.

Upon activation, p38mapk, p42mapk and p44mapk translocate to the nucleus and induce changes in the pattern of gene expression. Activation of p42mapk and p44mapk is via the action of the specific kinase, MEK (Mitogen-activated/Extracellular signal regulated kinase, MAP kinase kinase). MEK is, in turn, activated by any one of a group of kinases, including Raf and a MEK kinase. Hence, MEK, Raf, and/or MEK kinase lie downstream of, and are activated by, specific member(s) of the PKC family. These observations also suggest that MEK may function as an integrator for potentially hypertrophic stimuli in the cardiac myocyte.

A combination of in vivo and in vitro biochemical and pharmacological approaches are being employed to study the organization, specificity and roles of p42/44 and p38 map kinase signalling and how these relate to changes in cardiac growth and function evoked by hypertrophic stimuli. In addition, the roles of the endothelin receptor subtypes ETA and ETB, located at the cell surface and on the nuclear membrane, are being examined. This information should further the understanding of both signal transduction in the healthy heart and the defects which impair the ability of the heart to function in a normal manner, thereby identifying suitable targets for pharmacological intervention in the treatment of heart diseases.

Chevalier D, Allen BG. Two distinct forms of MAPKAP kinase-2 in adult cardiac ventricular myocytes. Biochemistry 39: 6145-6156, 2000

Chevalier D, Thorin E, Allen BG. Simultaneous measurement of MAP kinase cascades in vascular smooth muscle cells. J Pharmacol Toxicol Meth 44: 429-439, 2000

Allen BG, Phuong LL, Farhat H, Chevalier D. Both endothelin-A and endothelin-B receptors are present on adult rat cardiac ventricular myocytes. Can J Physiol Pharmacol 81: 95-104, 2003

Boivin B, Allen BG. Regulation of the plasma membrane-bound PKC in adult cardiac ventricular myocyte. Cell Signal 15: 217-224, 2003

Boivin B, Chevalier D, Villeneuve LR, Rousseau E, Allen BG. Localization of functional endothelin receptors on the nuclei in cardiac ventricular myocytes. J Biol Chem 278: 29153-29163, 2003

Benoit M-J, Rindt H, Allen BG. Cardiac-specific transgenic overexpression of alpha1B-adrenergic receptors induce chronic activation of ERK MAPK signalling. Biochem Cell Biol 82: 719-727, 2004

Farhat H, Allen BG. Salicylic acid alters endothelin-1 binding in intact adult rat ventricular myocytes. Biochem. Cell Biol 82: 728-738, 2004

Boivin B, Villeneuve LR, Farhat N, Chevalier D, Allen BG. Subcelluar distribution of endothelin signalling pathway components in ventricular myocytes and heart: Lack of preformed caveolar signalosomes. J Mol Cell Cardiol 38: 665-676, 2005

Boivin B, Lavoie C, Villeneuve LR, Ethier N, Allen BG, Hébert TE. Differential subcellular distributions of beta-AR subtypes and their effector molecules in adult rat ventricular cardiomyocytes. Cardiovasc Res 2006 (in press)