Searchable abstracts of presentations at key conferences in endocrinology
Endocrine Abstracts (2007) 14 OC9.7

ECE2007 Oral Communications Signal transduction (7 abstracts)

Seven transmembrane receptors mediated actin cytoskeleton rearrangement: comparison with constitutively active mutants of G protein alpha-subunits

Alenka Hrovat , Robert Frangez , Azra Pogacnik & Milka Vrecl


Veterinary Faculty, University of Ljubljana, Ljubljana, Slovenia.


Reorganization of the actin cytoskeleton could coincide with the activation of several seven transmembrane receptors (7TM receptors) (1). Stimulation of Rho family members leads to rapid remodeling of the actin cytoskeleton and subsequent stress fiber formation and certain 7TM receptors were shown to induce Rho-dependent responses via heterotrimeric G-proteins. Gα12, Gα13 as well as Gαq/11 can link 7TM receptors to RhoA activation. However, some controversy exists over the exact role of Gαq/11 (2).

The study’s aim was to examine whether activation of the Gαq/11- and Gαs-coupled 7TM receptors involves changes in cell morphology and reorganization of the actin cytoskeleton. Actin cytoskeletal organization was also monitored in cells transfected with constitutively active mutants of Gprotein α-subunits and compared with the receptor-mediated redistribution pattern. Autofluorescently-tagged β-actin (pEYFP-actin) was co-expressed together with receptor constructs (neurokinin type 1 receptor (NK1-R) and β2adrenergic receptor, β2-AR)) or constitutively active mutants of Gαq, Gα12, and Gαs in the HEK 293 cells. Evaluation of the autofluorescently-labeled actin filaments was performed with the use of confocal microscope.

The acquired data shows that the Gαq/11-coupled NK1-R activation caused changes in cell morphology, enhancement in the cortical actin signal and stress fiber formation. After the activation of other Gαq/11-coupled receptors comparable results were also observed. Furthermore, the presence of over-expressed constitutively active Gαq and Gα12 also lead to noticeable stress fiber formation. In contrast, neither the β2-AR activation nor constitutively active mutant of Gαs caused any apparent changes in actin cytoskeleton status in the HEK-293 cells. Based on these findings it could be assumed that only Gαq/11-coupled receptors activation coincides with the robust changes in the actin cytoskeleton organization.

References:

1. Merrifield CJ. Trends in Cell Biology 2004 14 352–358.

2. Barnes WG, Reiter E, Violin JD, Ren XR, Milligan G, Lefkowitz RJ. Journal of Biological Chemistry 2005 280 8041–8050

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