| Caveolae are non-clathrin, flask-shaped invaginations of the plasma membrane. Caveolin-1 is an essential constituent of caveolae and as such acts as a regulator of caveolaedependent signaling and endocytosis. Caveolin-1 interacts with a variety of cellular proteins through it scaffolding domain and regulates numerous cell signaling events. Caveolin-1 levels are down-regulated in many (although not all) primary human cancers and cancer cell lines, and in oncogene-transformed cells. In contrast, caveolin-1 is up-regulated in several multidrug resistant (MDR) and metastatic cancer cell lines and tumor specimens. Although caveolin-1 was initially suggested to act as a tumor suppressor, current evidence indicates that it may act also as a pro-survival protein in cancer cells.;We hypothesized that, at early stages of cancer progression, the growth inhibitory action of caveolin-1 restrains tumor expansion. However, at later stages of the disease, when metastatic and drug resistant phenotypes are prevalent, the survival-promoting activity of caveolin-1 becomes advantageous. Therefore, the main objective of this research was to explore this model by studying the role of caveolin-1 in tumor cells that express high levels of the protein.;In order to elucidate how expression of caveolin-1 contributes to multidrug resistance we used HT-29-MDR cells, a multidrug resistant cell line derived from colon cancer cell line HT-29. We examined the response of HT-29-MDR cells with modified caveolin-1 level to doxorubicin, colchicine and cisplatin. Suppression of caveolin-1 levels in HT-29-MDR cells has little or no effect on drug-induced loss of cell viability. However, G2/M arrest caused by cisplatin treatment was more prominent in HT-29-MDR with suppressed levels of caveolin-1.;To examine the impact of caveolin-1 expression on maintenance of metastasis-related phenotype we used H1299 non-small cell lung carcinoma cells. Herein, we show that suppression of endogenous caveolin-1 by shRNA impairs clonogenic growth, reduces cell invasion and chemoattractant-induced cell migration in H1299 cells. Overexpression of caveolin-1 mutants P132L-mRed and Y14F-mRed mimics RNAi phenotype, suggesting that they act in dominant negative manner. Expression of these mutants inhibits chemotactic migration, reduces cell invasion and increases stability of focal adhesion. During random and scratch-induced migration of H1299 cells, caveolin-1-mRed and its mutants are localized to the trailing edge of the cells, supporting an active role that caveolin-1 may play in regulation of cell migration.;To obtain a comprehensive and non-biased picture of the impact of caveolin-1 on cancer cell phenotype we performed a transcriptional profiling of H1299 cells following RNAi-mediated suppression of caveolin-1 levels. Our results reveal that the levels of several growth arrest and DNA-damage-inducible transcripts such as ATF3, ATF4, GADD45B, MAFF and PPP1R15A were up-regulated upon caveolin-1 knockdown, although many of down-regulated proteins are extracellular or secreted proteins, functionally associated with cell adhesion and motility like integrin beta5, laminin beta1, fibrillin-1 and FAM3C. The results allow us to delineate possible molecular mechanisms of the observed caveolin-1-dependent phenotypes as well as to look for novel caveolin-1-mediated functions.;Taken together, the results implicate caveolin-1 as a regulator of the variety of physiological processes including cell motility, invasiveness and cell cycle progression, and are consistent with a tumor-promoting role that caveolin-1 may play in advanced-stage cancer cells. |
