My laboratory is interested in the signal transduction mechanisms through which G-protein coupled receptors (GPCRs) regulate cell growth and cytoskeletal responses. Our work focuses on the role of heterotrimeric GPCRs coupled to the Gq and G12 proteins and to the low molecular weight G-protein Rho. We study astroglial cells and primary mouse brain astrocytes in which agonists for the muscarinic, thrombin and lysophospholipid (LPA and S1P) receptors have differential abilities to induce gene expression, elicit cytoskeletal changes and cell migration, and stimulate mitogenesis. Activation of small G-proteins in the Rho family are examined as key triggers for responses to cell injury and metastatic cell growth. Vascular smooth muscle cell responsiveness to these ligands is also under study since Rho signaling pathways appear to be critical components in control of vascular pathophysiology. Cell and molecular techniques including microinjection, immunocytochemistry, adenoviral infection, cDNA microarrays and transgenic and knockout mice are utilized to screen for signaling molecules and genes selectively regulated by growth promoting GPCRs. We also study the signaling pathways leading to cardiac hypertrophy and heart failure using isolated cardiomyocytes and transgenic and knockout mice. We are particularly interested in the role of Gq and Rho-proteins, and protein kinases including Ca++/CaM dependent kinase and AKT in the induction of cardiac gene expression, altered Ca++ homeostasis and control of apoptosis through mitochondrial permeability changes. Our studies indicate that cardiomyocyte apoptosis and protection against ischemic damage can be regulated via G-protein coupled receptor activation and suggest new approaches to inhibit cardiomyocyte loss and limit its role in pathophysiology.
Seasholtz T.M., Huang J.R., Sagi S.A., Matteo R., Weems J.M., Stoudt A., Feramisco J.R., Brown J.H. Rho-mediated cytoskeletal rearrangement in response to LPA is functionally antagonized by Gi, Rac1 and PIP2 signaling. J Neurochem, 91:501-512, 2004.
Del Re D.P., Miyamoto S. and Brown J.H. RhoA/Rho kinase upregulate Bax to activate a mitochondrial death pathway and induce cardiomyocyte apoptosis. J Biol Chem. 282/11:8069-8078, 2007.
Radeff-Huang J., Seasholtz T.M., Chang J.W., Smith, J.M., Walsh, C.T. and Brown J.H. Tumor necrosis factor-alpha-stimulated cell proliferation is mediated through sphingosine kinase-dependent Akt activation and cyclin D expression. J Biol Chem. 282/2:863-870, 2007.
Means C.K., Xiao C.Y., Li Z., Zhang T., Omens J.H., Ishii I., Chun J., Brown J.H., Sphingosine 1 Phosphate S1P2 and S1P3 receptor-mediated Akt activation protects against in vivo myocardial ischemia-reperfusion injury. Am J Physiol Heart Circ Physiol. 292:2944-2951, 2007.
Citro S., Radeff-Huang J., Kelley G.G., Smrcka A. and Brown J.H. Phospholipase C-epsilon is a nexus for Rho and Rap-mediated GPCR induced astrocyte proliferation. Proc Natl Acad Sci U S A. 104:15543-48, 2007.
Wu X., Zhang T., Bossuyt J., Li X., McKinsey T., Dedman J.R., Olson E.N., Chen J., Brown J.H., Bers D.M. Local InsP3-dependent perinuclear Ca2+ signaling in cardiac myocyte excitation-transcription coupling. J Clin Invest, 116:675-82, 2006.