RhoA phosphorylation

A. RhoA Phosphorylation Is Complex and Regulates Its Protein Protein Interactions, Activation, and Effector Binding... 

The interaction between RhoA and its key effector Rho-associated kinase (ROK or ROCK) is decreased upon RhoA phosphorylation, as shown by pull-down assays [71], and RhoA phosphorylation is also inversely correlated with signaling to its downstream effector phosphoh-pase D (PLD) [76,81]. However, not all effects of RhoA phosphorylation can be attributed to increased binding to RhoGDI leading to decreased signaling. RhoA expressed in bacteria (i.e., nonprenylated) and phosphorylated in vitro bound less efficiently to its downstream effector ROK in vitro than did nonphosphorylated RhoA [65]. Since this was done without any RhoGDI present, there must be something intrinsic about RhoA phosphorylation that affects RhoA interactions with at least some of its... 

Tamma, G., Klussmann, E., Procino, G., Svelto, M., Rosenthal, W., and Valenti, G. (2003). cAMP-induced AQP2 translocation is associated with RhoA inhibition throngh RhoA phosphorylation and interaction with RhoGDI. J Cell Sci 116 1519-1525. 

A subfamily of Rho proteins, the Rnd family of small GTPases, are always GTP-bound and seem to be regulated by expression and localization rather than by nucleotide exchange and hydrolysis. Many Rho GTPase effectors have been identified, including protein and lipid kinases, phospholipase D and numerous adaptor proteins. One of the best characterized effector of RhoA is Rho kinase, which phosphorylates and inactivates myosin phosphatase thereby RhoA causes activation of actomyosin complexes. Rho proteins are preferred targets of bacterial protein toxins ( bacterial toxins). 

Hirase T, Kawashima S, Wong EYM, Ueyama T, Rikitake Y, Tsukitai S, Yokoyama M, and Staddon JM [2001] Regulation of tight junction permeability and Occludin phosphorylation by RhoA-pl60ROCK-dependent and -independent mechanisms. J Biol Chem 276 10423-10431... 

Figure 5 Signaling of cell growth through NGF and NGFR TrkA. Binding of NGF to TrkA results in TrkA auto-phosphorylation. The phosphorylated receptor can interact with She and triggers the Ras/Raf/MEK pathway. Phosphorylation of ELK-1 initiates gene transcription and cell growth. Ras also activates RhoA, which inhibits the growth arrest protein p21°" .

Ellerbroek SM, Wennerberg K, Burridge K (2003) Serine phosphorylation negatively regulates RhoA in vivo. J Biol Chem 278 19023-31... 

Zhuang S, Nguyen GT, Chen Y, Gudi T, Eigenthaler M, Jarchau T, Walter U, et al. (2004) Vasodilator-stimulated phosphoprotein activation of serum-response element-dependent transcription occurs downstream of RhoA and is inhibited by cGMP-dependent protein kinase phosphorylation. J Biol Chem 279 10397 407... 

Not all 5-HT4 receptor effects are mediated by cAMP. 5-HT4 receptors inhibit the sodium-proton exchanger isoforms NHE-2 and NHE-3 in human intestinal epithelial cells and T-84 cells through Src-dependent phosphorylation of PLC-y, elevation of intracellular Ca2+ levels, and subsequent activation of PKC-a (339). 5-HT4e receptors increase phosphoinositide hydrolysis in CHO cells (329). 5-HT4a receptors in neuroblastoma x glioma NIE-115 cells cause G13o, and RhoA-dependent neurite retraction and cell rounding. 

Fig. 20.3 Schematic showing a pivotal role of RhoA/ROCK activation as a mediator of leptin-induced hypertrophy and its interaction with p38. Activation of RhoA/ROCK results in increased cofilin phosphorylation and altered actin dynamics as demonstrated by a decreased G/F-actin ratio. Stimulation of this pathway results in an exclusive and selective translocation of p38 MAPK into the nucleus which results in an increased protein synthesis to an as yet to be identified mechanism.

The effects of RhoA activity on spine number and morphology are mediated, at least in part, by the RhoA effector, Rho kinase (Nakayama et al., 2000 Tashiro and Yuste, 2004 Yuste and Bonhoeffer, 2004). Different targets of Rho-kinase have been identified, such as LIMK, myosin light chain (MLC), and MLC phosphatase. Rho-kinase phosphorylates and activates LIMK, which in turn phosphorylates and inactivates the actin depolymerization factor (ADF) cofilin (Maekawa et al., 1999 Sumi et al., 1999 Ohashi et al., 2000 Amano et al., 2001). Phosphorylation of MLC by Rho-kinase results in the stimulation of myosin-actin interactions (Amano et al.,... 

Like RhoA, RhoB is also phosphorylated within its hypervariable domain [86]. In 2008, Pradines and colleagues showed that CKl is capable of phos-phorylating RhoB in vitro and in cellulo at serine 185 [86]. This phosphorylation was independent of the nucleotide bound to RhoB because both constitutively active (G14V) and wild-type RhoB were phosphorylated to similar extents [86]. It is currently unknown how this phosphorylation relates... 

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