Polymerase I and transcript release factor (PTRF, also known as Cavin-1) is an essential component in the biogenesis and function of caveolae. Here, we show that PTRF expression is increased in senescent human fibroblasts. Importantly, overexpression of PTRF induced features characteristic of cellular senescence, whereas reduced PTRF expression extended the cellular replicative lifespan. Interestingly, we found that PTRF localized primarily to the nuclei of young and quiescent WI-38 human fibroblasts, but translocated to the cytosol and plasma membrane during cellular senescence. Furthermore, electron microscopic analysis demonstrated an increased number of caveolar structures in senescent and PTRF-transfected WI-38 cells. Our data suggest that the role of PTRF in cellular senescence is dependent on its targeting to caveolae and its interaction with caveolin-1, which appeared to be regulated by the phosphorylation of PTRF. Taken together, our findings identify PTRF as a novel regulator of cellular senescence that acts through the p53/p21 and caveolar pathways.

Caveolae are abundant membrane domain on the cell surface of many mammalian cell types and are implicated in a wide range of physiological processes. The caveolae structural protein caveolin-1 is often mutated or deregulated in cancer, and cavin family protein serum deprivation response factor-related gene product that binds to C-kinase (SRBC) has been found to be epigenetically inactivated in lung, breast, and gastric cancer. Both caveolin-1 and SRBC have been proposed to function as tumor suppressors. Polymerase 1 and transcript release factor (PTRF) is the essential component for caveolae formation. The regulation of PTRF expression in cancer has not been characterized. We report here that the cavin family protein PTRF, SRBC and serum deprivation response protein were down regulated in breast cancer cell lines and breast tumor tissue. We further show that down-regulation of PTRF in breast cancer cells was associated with the promoter methylation. As caveolin-1 and cavin family proteins are required for caveolae formation and function, the reported tumor suppression function of caveolin-1 and SRBC may be due to the deregulation of caveolae and its down-stream signaling. Thus, the caveolae is a potential therapeutic target and the expression of cavin family proteins could be a useful prognostic indicator of breast cancer progression.

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Fluctuations in serum autofluorescence (AF) intensity have recently been widely used as markers of certain diseases such as cancer. To determine the diagnostic value of serum AF intensity for liver fibrosis in rats, we induced liver fibrosis by subcutaneous injection of carbon tetrachloride into rats. The rat serum AF intensities were detected at the excitation wavelength of 337 nm and the emission wavelength of 512 nm. The degree of liver fibrosis was evaluated by Van Gieson’s staining. The relationship between serum AF intensity and the degree of liver fibrosis was analyzed by Spearman and Pearson Correlation. The diagnostic sensitivity and specificity of the serum AF was determined by analyzing the receiver operating characteristic (ROC) curves. Our results show that the serum AF intensity in the rat liver fibrosis model increased when compared with control rats eight weeks and twelve weeks post induction of liver fibrosis. However, there was no significant difference in serum AF intensity between fibrotic and control rats at four week post induction. Furthermore, serum AF intensity correlated positively with the severity of the degree of hepatic fibrosis. ROC analysis further suggested that serum AF intensity is a valid marker for staging fibrosis. Therefore, it may potentially be developed as a novel diagnostic tool for hepatic fibrosis.