Caveolin-1 is involved in reactive oxygen species-induced SHP-2 activation in astrocytes

Recent evidence supports a neuroprotective role of Src homology 2-containing protein tyrosine phosphatase 2 (SHP-2) against ischemic brain injury. However, the molecular mechanisms of SHP-2 activation and those governing how SHP-2 exerts its function under oxidative stress conditions are not well understood. Recently we have reported that reactive oxygen species (ROS)-mediated oxidative stress promotes the phosphorylation of endogenous SHP-2 through lipid rafts, and that this phosphorylation strongly occurs in astrocytes, but not in microglia. To investigate the molecules involved in events leading to phosphorylation of SHP-2, raft proteins were analyzed using astrocytes and microglia. Interestingly, caveolin-1 and -2 were detected only in astrocytes but not in microglia, whereas flotillin-1 was expressed in both cell types. To examine whether the H2O2-dependent phosphorylation of SHP-2 is mediated by caveolin-1, we used specific small interfering RNA (siRNA) to downregulate caveolin-1 expression. In the presence of caveolin-1 siRNA, the level of SHP-2 phosphorylation induced by H2O2 was significantly decreased, compared with in the presence of control siRNA. Overexpression of caveolin-1 effectively increased H2O2-induced SHP-2 phosphorylation in microglia. Lastly, H2O2 induced extracellular signal-regulated kinase (ERK) activation in astrocytes through caveolin-1. Our results suggest that caveolin-1 is involved in astrocyte-specific intracellular responses linked to the SHP-2-mediated signaling cascade following ROS-induced oxidative stress.

A second protein marker of caveolae: caveolin-2 / 中国医学科学杂志(英文版)

Caveolin-2, a protein about 20 kD, is a major component of the inner surface of caveolae, small invaginations of the plasma membrane. Similar with caveolin-1 and caveolin-3, it serves as a protein marker of caveolae. Caveolin-1 and -2 are located next to each other at 7q31.1 on human chromosome, the proteins encoded are co-localized and form a stable hetero-oligomeric complex, distributing similarly in tissue and cultured cells. Caveolin-3 is located on different chromosomes but confirmed to interact with caveolin-2. Caveolin-2 is similar to caveolin-1 in many respects but differs from the latter in functional domains, especially in G-protein binding domain and caveolin scaffolding domain. The mRNAs of both caveolin-1 and caveolin-2 are most abundantly expressed in white adipose tissue and are induced during differentiation of 3T3-L1 cells to adipocytes. Caveolin-2-deficient mice demonstrate clear pulmonary defects, with little or no change in caveolin-1 expression and caveolae formation, suggesting that caveolin-2 plays a selective role in lung functions. Caveolin-2 is also involved in lipid metabolism and human cancers.

Expression of Caveolin in Hepatocellular Carcinoma: Association with Unpaired Artery Formation and Radiologic Findings / 대한간학회지

BACKGROUND/AIMS: Hepatocellular carcinoma (HCC) is becoming one of the common malignant tumors worldwide, and it is characterized by its high vascularity. Caveolin is the major structural protein in caveolae, which are small omega-shaped invaginations within the plasma membrane. Caveolin has been implicated in mitogenic signaling, oncogenesis and angiogenesis. The expression of caveolin-1 and -2 in HCC and its potential relationship with angiogenesis has not been examined. METHODS: Paraffin sections of 35 HCC specimens were immunostained with caveolin-1, caveolin-2, alpha-smooth muscle actin, and CD34 antibodies. In addition, the expression of caveolin-1 and -2 mRNA in HCC was examined. The relationship between the radiological findings and the number of unpaired arteries and microvessel density (MVD) was also investigated. RESULTS: Caveolin-1 and -2 were expressed in the sinusoidal endothelial cells in 20 out of 35, and 18 out of 35 HCC specimens, respectively. Caveolin-1 and -2 were also expressed in the smooth muscle cells of the unpaired arteries in 26 out of 35, and 18 out of 35 HCC specimens, respectively. Increased expression of caveolin-1 and -2 mRNA was detected in 26.7% and 33.3% of the tumor specimens, respectively, compared with the corresponding non-tumorous adjacent liver tissues. There was a significant correlation between expression of caveolin-1, -2 in the smooth muscle cells of unpaired arteries and the number of unpaired arteries. The number of unpaired arteries in HCCs was found to be associated with the degree of contrast enhancement in the arterial phase imaging. However, it did not correlate with the degree of MVD. CONCLUSIONS: These findings suggest that the expression of caveolin-1, -2 is associated with the formation of unpaired arteries in HCC. In addition, there is a correlation between the degree of contrast enhancement of the HCC in the arterial phase image and the number of unpaired arteries.

Immunohistochemical study of caveolin-1 and -2 in the rat retina

The expression of caveolin-1 and -2 in the retina was examined; Western blot analysis showed that both were present. Immunohistochemistry indicated that caveolin-1 was expressed in the majority of retinal layers, including the ganglion cell layer, inner plexiform layer, outer plexiform layer, and in the vascular endothelial cells of the retina. Caveolin-2 was primarily immunostained in the vessels, but in a few other elements as well. This is the first demonstration of caveolin differential expression in the retina of rats, and suggests that caveolin plays an important role in signal transduction in glial cells and neuronal cells.

Rat Organic Anion Transporter 3 Co-localized with Caveolin-2 in Rat Kidney / 대한신장학회잡지

BACKGROUND: The recently identified organic anion transporter 3 (rOAT3) was mainly expressed in kidney, liver and brain tissue, and it contributes the movement of endogenous or exogenous substances across the cell membrane. Although the properties of rOAT3 are gradually accumulated, the regulatory mechanism of rOAT3 remains to be elucidated. Caveolin (Cav) also plays a role as a membrane transporter and as a modulating protein for some functional proteins. Therefore, we investigated the protein-protein interaction between rOAT3 and Cav-2 in rat kidney. METHODS: The expressions of rOAT3 and Cav-2 (mRNA and protein) were observed using RT-PCR and Western blot analysis. The localization of rOAT3 and Cav-2 was determined in the caveolae-rich membrane fraction isolated by sucrose gradient ultra-centrifugation. For the direct binding between the rOAT3 and Cav-2 proteins, the immuno-precipitation method and confocal microscopy were employed. In order to perform functional analysis, a Xenopus oocytes expression system with the antisense oligodeoxynucleotides (ODN) technique was used. RESULTS: The expressions of rOAT3 and Cav-2 (mRNA and protein) were detected in the kidney. The caveolae-rich membranous fractions from the kidney contained both rOAT3 and Cav-2 in the same fractions. The immuno-precipitation experiments showed the formation of a complex between the rOAT3 and Cav-2 in the kidney. The confocal microscopic results using primary cultured renal proximal epithelial cells also supported the co-localization of rOAT3 and Cav-2 at the plasma membrane. The uptake function of rOAT3, as tested for by using a Xenopus oocytes expression system was slightly inhibited (with statistical significance) by the Xenopus Cav-2 antisense ODN. CONCLUSION: rOAT3 co-localizes with caveolin-2 in the caveolae, and caveolin-2 plays an important role in regulating the function of rOAT3.