In my previous post Small GTPases: Measuring small G protein activation I looked at state-of the-art methods for measuring the activation of small G proteins, such as RhoA, Rac1, Cdc42, and the proto-oncogen Ras. Today, I invite you to explore some methods for measuring the activity of Guanine nucleotide Exchange Factors (GEFs).

Fig. 1: Small G protein activation cycle

In this post, I invite you to discover some state-of-the art methods to measure the activation of the most prominent small G proteins. In future posts, we’ll then be looking at methods to measure the activity of Guanine nucleotide exchange factors (GEFs) which stimulate the release of GDP to allow the binding of GTP (which activates the small G protein) and of GTPase-activating proteins (GAPs) which stimulate the GTPase activity of small G proteins to inactive them (see Fig. 1).

Post-translational Modifications of RhoA

Rho family GTPases are key regulators in a wide range of physiological processes, including cell motility, cell division, and neuronal development. Rho activity is regulated temporally and spatially by a variety of direct post-translational modifications (PTMs) that include prenylation, ubiquitination, oxidation, nitrosylation, and phosphorylation.

Cytoskeleton Inc. recently released a newsletter highlighting the control of RhoA function through phosphorylation. RhoA is a target for a growing number of kinases and as such, phosphorylation is emerging as a central theme in the regulation of this family of proteins (2).

The newsletter focussed on the mechanism of RhoA phosphorylation at Serine 188, which is mainly conducted by kinases like PKA and PKG (protein kinase A and protein kinase G) which are cyclic AMP-dependent and cyclic GMP-dependent respectively.

Furthermore, it looks at the physiological consequences of RhoA phosphorylation and future directions especially concerning the RhoA PTM involvement in diseases and potential  therapeutic options.

You can download a copy of this newsletter, or if you have any questions or comments, don’t hesitate to contact me through the form below.

Related to RhoA and PTM research:

• G-LISA kits to measure the activation of RhoA
• Cell permeable RhoA inhibitor (C3Transferase)
• RhoA activators
• Anti Acetyl Lysine Mouse Monoclonal Antibody
• Anti-SUMO1 Mouse Monoclonal Antibody
• Anti-Ubiquitin Mouse Monoclonal Antibody

References:

1. Stankiewicz T. & Linseman D. 2014. Rho family GTPases: key players in neuronal development, neuronal survival and neurodegeneration. Front. Cell. Neurosci. doi: 10.3389/fncel.2014.00314.
2. Boulter E. et al. 2012. Off the beaten paths: alternative and crosstalk regulation of Rho GTPases. FASEB J. 26, 469-479.

Recently, R. Palanivel et al. investigated the role that RhoA-mediated re-organization of the actin cytoskeleton has in adiponectin-regulated glucose uptake in cardiomyocytes.  Adiponectin is a protein secreted by adipose tissue that modulates glucose and fatty acid metabolism.  In concert with APPL1, an adiponectin receptor binding partner, adiponectin carries out these functions which are important in obesity and type 2 diabetes, two diseases that reduce cardiac energy metabolism. The authors found that adiponectin (both full-length and globular) elevates RhoA activity which correlates with increased actin polymerization and glucose uptake.  Changes in the G-/F-actin ratio likely involve APPL1 as adiponectin increases colocalization of actin and APPL1.  Inhibition of actin polymerization or RhoA signaling significantly reduces the adiponectin-mediated increase in glucose uptake.  Thus, RhoA-mediated actin cytoskeleton remodeling is required for adiponectin-regulated glucose uptake in cardiomyocytes.  Increased glucose uptake is cardioprotective in diabetes. A number of products by Cytoskeleton Inc. (“The Protein Experts”) were essential in this study, providing accurate and sensitive assays for quantifying levels of activated RhoA and changes in G- and F-actin levels or binding partners in cardiomyocytes under conditions of RhoA inhibition.

• RhoA G-LISA activation assay 
• G-/F-actin In Vivo Assay Kit
• Anti-actin antibody
• Cell-permeable Rho inhibitor

These reagents are available in Europe through tebu-bio, who have also compiled useful selection tools:

• Actin Product Guide

• Small G Protein Product Guide

Reference: Palanivel et al. 2014. Adiponectin stimulates Rho-mediated actin cytoskeleton remodeling and glucose uptake via APPL1 in primary cardiomyocytes. Metabolism. 63, 1363-1373.