Low molecular weight GTP-binding proteins are molecular switches that are believed to play pivotal roles in cell growth, differentiation, cytoskeletal organization, and vesicular trafficking. Rab proteins are key players in the regulation of vesicular transport, while Rho family members control actin-dependent cell functions, i.e. the regulation of cytoskeletal organization in response to extracelluar growth factors and in dendritic neuron development. In this study, we have examined the regulation of small GTP-binding proteins that are implicated in neurosecretion and differentiation of neuron during ageing processes. Comparison of small GTP-binding proteins from the synaptosome and crude synaptic vesicles (LP2 membranes) of 2 months and 20 months old rat brain respectively showed no difference in the level of Rab family proteins (Rab3A and Rab5A). However, Rho family proteins such as RhoA and Cdc42 were elevated in LP2 membranes of the aged brain. The dissociation of Rab3A by Ca2+/calmodulin (CaM) from SV membranes was not changed during aging. Ca2+/CaM stimulated phosphorylation of the 22 and 55-kDa proteins in SV membranes from the aged rat brain, and inhibited phosporylation of 30-kDa proteins. GTPgammaS inhibited phosphorylation of the 100-kDa proteins and stimulated phosphorylation of the 70 kDa in LP2 membranes from both the young and aged rat brains, whereas GDPbetaS caused just the opposite reaction. These results suggest that protein phosphorylation and regulation of Rho family GTPases in rat brain appears to be altered during ageing processes.
*Aging ; Animal ; Brain/metabolism ; Calcium/pharmacology ; Cattle ; Comparative Study ; GTP-Binding Proteins/*metabolism ; Guanosine 5'-O-(3-Thiotriphosphate)/metabolism ; Molecular Weight ; Phosphorylation/drug effects ; Rats ; Rats, Sprague-Dawley ; Synaptic Membranes/*metabolism ; Synaptosomes/*metabolism ; cdc42 GTP-Binding Protein/biosynthesis/metabolism ; rab3A GTP-Binding Protein/metabolism ; rab5 GTP-Binding Proteins/metabolism ; rhoA GTP-Binding Protein/biosynthesis/metabolism

Low molecular weight GTP-binding proteins are molecular switches that are believed to play pivotal roles in cell growth, differentiation, cytoskeletal organization, and vesicular trafficking. Rab proteins are key players in the regulation of vesicular transport, while Rho family members control actin-dependent cell functions, i.e. the regulation of cytoskeletal organization in response to extracelluar growth factors and in dendritic neuron development. In this study, we have examined the regulation of small GTP-binding proteins that are implicated in neurosecretion and differentiation of neuron during ageing processes. Comparison of small GTP-binding proteins from the synaptosome and crude synaptic vesicles (LP2 membranes) of 2 months and 20 months old rat brain respectively showed no difference in the level of Rab family proteins (Rab3A and Rab5A). However, Rho family proteins such as RhoA and Cdc42 were elevated in LP2 membranes of the aged brain. The dissociation of Rab3A by Ca2+/calmodulin (CaM) from SV membranes was not changed during aging. Ca2+/CaM stimulated phosphorylation of the 22 and 55-kDa proteins in SV membranes from the aged rat brain, and inhibited phosporylation of 30-kDa proteins. GTPgammaS inhibited phosphorylation of the 100-kDa proteins and stimulated phosphorylation of the 70 kDa in LP2 membranes from both the young and aged rat brains, whereas GDPbetaS caused just the opposite reaction. These results suggest that protein phosphorylation and regulation of Rho family GTPases in rat brain appears to be altered during ageing processes.
*Aging ; Animal ; Brain/metabolism ; Calcium/pharmacology ; Cattle ; Comparative Study ; GTP-Binding Proteins/*metabolism ; Guanosine 5'-O-(3-Thiotriphosphate)/metabolism ; Molecular Weight ; Phosphorylation/drug effects ; Rats ; Rats, Sprague-Dawley ; Synaptic Membranes/*metabolism ; Synaptosomes/*metabolism ; cdc42 GTP-Binding Protein/biosynthesis/metabolism ; rab3A GTP-Binding Protein/metabolism ; rab5 GTP-Binding Proteins/metabolism ; rhoA GTP-Binding Protein/biosynthesis/metabolism

OBJECTIVETo investigate the expression of RhoA, RhoC and their effector ROCK-1 in four ovarian cancer cell lines in vitro and their correlation with invasiveness.

METHODSExpression of RhoA, RhoC and ROCK-1 mRNA and protein in four ovarian cancer cell lines SW626, Skov-3, A2780 and Caov-3 was detected by RT-PCR and Western blot assay. Invasion assay was done in Boyden chamber.

RESULTSThe expression levels of RhoA, RhoC and ROCK-1 mRNA and protein varied in the four different cell lines examined. The expression level of RhoC, but not RhoA and ROCK-1, was significantly correlated with the invasive capability of these cells in vitro (r = 0.95, P < 0.01). Expression of RhoA at the level of transcription was not correlated with that at the translation level. The expression of RhoA and RhoC did not correlate with that of ROCK-1.

CONCLUSIONExpression level of RhoC may serve as an independent parameter in evaluating metastasis and become a new target in inhibiting ovarian cancer metastasis.

Cell Line, Tumor ; Cell Movement ; Female ; Gene Expression Regulation, Neoplastic ; Humans ; Intracellular Signaling Peptides and Proteins ; Neoplasm Invasiveness ; Neoplasm Metastasis ; Ovarian Neoplasms ; genetics ; metabolism ; pathology ; Phenotype ; Protein Biosynthesis ; Protein-Serine-Threonine Kinases ; biosynthesis ; genetics ; RNA, Messenger ; biosynthesis ; genetics ; Transcription, Genetic ; rho GTP-Binding Proteins ; biosynthesis ; genetics ; rho-Associated Kinases ; rhoA GTP-Binding Protein ; biosynthesis ; genetics ; rhoC GTP-Binding Protein

RhoA is one of the main members of RhoGTPase family involved in cell morphology, smooth muscle contraction, cytoskeletal microfilaments and stress fiber formation. It has been demonstrated that RhoA modulates endothelial cell permeability by its effect on F-actin rearrangement, but the molecular mechanism of rearrangement of actin cytoskeleton remains unclear. Recent studies prove that RhoA/Rho kinase regulates smooth muscle specific actin dynamics by activating serum response factor (SRF)-dependent transcription. To further investigate the molecular mechanism of the rearrangement of vascular endothelial cell actin cytoskeleton, we explored the relationship between the activation of SRF and F-actin rearrangement induced by RhoA in human umbilical vein endothelial cells (HUVECs). HUVECs were infected with the constitutively active forms of RhoA (Q63LRhoA) or the dominant negative forms of RhoA(T19NRhoA) using retrovirus vector pLNCX-Q63LRhoA or pLNCX-T19NRhoA, the positive clone was obtained by G418 selection. The expression and distribution of SRF in normal and infected cells were evaluated by immunohistochemistry and Western blot in complete medium and in serum-free medium. The effect of F-actin polymerization was detected by Rhodamine-Phalloidine staining. Infection of PLNCX-Q63LRhoA induced F-actin rearrangement and stress fiber formation in HUVECs, as well as enhanced the expression of SRF in the nuclei. In contrast, the cells infected with T19NRhoA showed no distinct changes. With serum deprivation, the expression of SRF increased obviously in both normal and infected HUVECs, but the subcellular localization of SRF was evidently different. In HUVECs, the localization of SRF was in the nuclei after 3 d with serum deprivation, but it was redistributed outside the nuclei after 5 d with serum deprivation. In cells infected with Q63LRhoA, the immunolocalization of SRF was always in the nuclei compared with HUVECs infected with T19NRhoA, which was almost always localized in the cytoplasm. In HUVECs, the rearrangement of F-actin and formation of stress fiber increased after 3 d with serum deprivation, but appeared decreased and unpolymerized after 5 d with serum deprivation. The polymerization of F-actin and the formation of stress fiber in HUVECs infected with Q63LRhoA kept during the period of serum-free culture, whereas the rearrangement of F-actin in cells infected with T19NRhoA was not found. These results suggest that RhoA influences endothelial F-actin rearrangement in part by regulating the expression and subcellular localization of SRF.
Actins ; biosynthesis ; genetics ; Cytoskeleton ; metabolism ; Endothelium, Vascular ; cytology ; metabolism ; Humans ; Intracellular Signaling Peptides and Proteins ; Protein-Serine-Threonine Kinases ; metabolism ; Serum Response Factor ; biosynthesis ; genetics ; Umbilical Veins ; cytology ; rho-Associated Kinases ; rhoA GTP-Binding Protein ; physiology