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.
Biomarkers ; metabolism ; Caveolae ; metabolism ; Caveolin 2 ; genetics ; metabolism ; Chromosomes, Human, Pair 7 ; Humans

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.
Adult ; Aged ; Carcinoma, Hepatocellular/*blood supply/metabolism/radiography ; Caveolin 1/genetics/*metabolism ; Caveolin 2/genetics/*metabolism ; Female ; Hepatic Artery/pathology/radiography ; Humans ; Liver Neoplasms/*blood supply/metabolism/radiography ; Male ; Middle Aged ; Neoplasm Staging ; Neovascularization, Pathologic/etiology/*metabolism/radiography ; Retrospective Studies

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.
Animals ; Astrocytes/*metabolism ; Caveolin 1/*genetics/metabolism ; Caveolin 2/genetics ; Cell Line ; Cells, Cultured ; Extracellular Signal-Regulated MAP Kinases/metabolism ; Gene Expression ; Humans ; Microglia/metabolism ; Phosphoric Monoester Hydrolases/*metabolism ; Phosphorylation ; Protein Tyrosine Phosphatase, Non-Receptor Type 11/*metabolism ; Rats ; Reactive Oxygen Species/*metabolism

It has been proposed that the pro-inflammatory catalytic activity of cyclooxygenase-2 (COX-2) plays a key role in the aging process. However, it remains unclear whether the COX-2 activity is a causal factor for aging and whether COX-2 inhibitors could prevent aging. We here examined the effect of COX-2 inhibitors on aging in the intrinsic skin aging model of hairless mice. We observed that among two selective COX-2 inhibitors and one non-selective COX inhibitor studied, only NS-398 inhibited skin aging, while celecoxib and aspirin accelerated skin aging. In addition, NS-398 reduced the expression of p53 and p16, whereas celecoxib and aspirin enhanced their expression. We also found that the aging-modulating effect of the inhibitors is closely associated with the expression of type I procollagen and caveolin-1. These results suggest that pro-inflammatory catalytic activity of COX-2 is not a causal factor for aging at least in skin and that COX-2 inhibitors might modulate skin aging by regulating the expression of type I procollagen and caveolin-1.
Animals ; Aspirin/administration & dosage ; Catalysis ; Caveolin 1/genetics/metabolism ; Collagen Type I/genetics/metabolism ; *Cyclooxygenase 2/metabolism/physiology ; Cyclooxygenase 2 Inhibitors/*administration & dosage ; Gene Expression Regulation ; Mice ; Nitrobenzenes/*administration & dosage ; Pyrazoles/administration & dosage ; Skin Aging/*drug effects/physiology ; Sulfonamides/*administration & dosage ; Tumor Suppressor Protein p53/genetics/metabolism

The purpose of this study was to demonstrate the cellular localization of cyclooxygenase-2 (COX-2) and caveolin-3 (Cav-3) in primarily cultured rat chondrocytes. In normal rat chondrocytes, we observed relatively high levels of Cav-3 and a very low level of COX-2 mRNA and protein. Upon treating the chondrocytes with 5 microM of CdCl2 (Cd) for 6 hr, the expressions of COX-2 mRNA and protein were increased with the decreased Cav-3 mRNA and protein expressions. The detergent insoluble caveolae-rich membranous fractions that were isolated from the rat chondrocytes and treated with Cd contained the both proteins of both COX-2 and Cav-3 in a same fraction. The immuno-precipitation experiments showed complex formation between the COX-2 and Cav-3 in the rat chondrocytes. Purified COX-2 with glutathione S-transferase-fused COX-2 also showed complex formation with Cav-3. Confocal and electron microscopy also demonstrated the co-localization of COX-2 and Cav-3 in the plasma membrane. The results from our current study show that COX-2 and Cav-3 are co-localized in the caveolae of the plasma membrane, and they form a protein-protein complex. The co-localization of COX-2 with Cav-3 in the caveolae suggests that the caveolins might play an important role for regulating the function of COX-2.
Animals ; Animals, Newborn ; Blotting, Western ; Cadmium Chloride/pharmacology ; Caveolae/drug effects/metabolism/ultrastructure ; Caveolin 3/*genetics/metabolism ; Cell Membrane/drug effects/metabolism ; Cells, Cultured ; Chondrocytes/cytology/drug effects/*metabolism ; Cyclooxygenase 2/*genetics/metabolism ; Gene Expression ; Immunoprecipitation ; Microscopy, Confocal ; Microscopy, Electron ; RNA, Messenger/genetics/metabolism ; Rats ; Reverse Transcriptase Polymerase Chain Reaction