Endocrine Abstracts

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 Gα_q/11 can link 7TM receptors to RhoA activation. However, some controversy exists over the exact role of Gα_q/11 (2).

The study’s aim was to examine whether activation of the Gα_q/11- and Gα_s-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 Gα_q, Gα₁₂, and Gα_s 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 Gα_q/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 Gα_q/11-coupled receptors comparable results were also observed. Furthermore, the presence of over-expressed constitutively active Gα_q and Gα₁₂ also lead to noticeable stress fiber formation. In contrast, neither the β₂-AR activation nor constitutively active mutant of Gα_s caused any apparent changes in actin cytoskeleton status in the HEK-293 cells. Based on these findings it could be assumed that only Gα_q/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