title: Caveolin-1 inhibits cell detachment-induced p53 activation and anoikis by upregulation of insulin-like growth factor-I receptors and signaling.
abstract: Caveolin-1 is an essential structural constituent of caveolae that has been implicated in mitogenic signaling and oncogenesis. Utilizing MCF-7 human breast cancer cells, stably transfected with caveolin-1 (MCF-7/Cav1), we previously demonstrated that caveolin-1 expression decreases MCF-7 cell proliferation and colony formation in soft agar. However, the loss of anchorage-independent growth is associated with inhibition of anoikis, as MCF-7/Cav1 cells exhibit increased survival after detachment. Herein we show that this phenotype is associated with suppression of detachment-induced activation of p53 and of the consequent induction of cyclin-dependent kinase inhibitor p21(WAF1/Cip1). In contrast, activation of p53 and p21(WAF1/Cip1) induced by doxorubicin in MCF-7/Cav1 cells remains largely unaffected. The phenotypic changes observed in MCF-7/Cav1 cells are not accompanied by changes in caspase-6, -7, -8 and -9 and cannot be explained by changes in Bid and Bcl-2 expression. However, MCF-7/Cav1 cells exhibit a constitutively phosphorylated Akt kinase and at least one phosphorylated high molecular weight putative Akt substrate which we designated pp340. In addition, MCF-7/Cav1 cells exhibit elevated expression of insulin-like growth factor-I (IGF-I) receptor expression and increased IGF-I signaling to Erk1/2 and to Akt, as well as IGF-I-induced stimulation of pp340 phosphorylation. The addition of IGF-I to the medium rescues the parental MCF-7 cells from anoikis, indicating that IGF-1 can act as a survival factor for suspended MCF-7 cells. Finally, the levels of caveolin-1 are dramatically elevated in a time-dependent manner upon detachment of anoikis-resistant MCF-7/Cav1 cells and HT-29-MDR human multidrug resistant colon cancer cells. We conclude that expression of caveolin-1 in human breast cancer cells enhances matrix-independent cell survival that is mediated by upregulation of IGF-I receptor expression and signaling.
authors.affiliation: Department of Biological Regulation, Weizmann Institute of Science, Candiotty 138, PO Box 26, Rehovot 76100, Israel.
authors.forename: Dana
authors.initials: D
authors.lastname: Ravid
authors.forename: Sharon
authors.initials: S
authors.lastname: Maor
authors.forename: Haim
authors.initials: H
authors.lastname: Werner
authors.forename: Mordechai
authors.initials: M
authors.lastname: Liscovitch
mesh_terms: D023102:Anoikis / Q000502:physiology*; D051023:BH3 Interacting Domain Death Agonist Protein; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D051242:Caveolin 1; D022461:Caveolins / Q000235:genetics / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000502:physiology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000502:physiology; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004249:DNA Damage; D004317:Doxorubicin / Q000494:pharmacology; D005109:Extracellular Matrix / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000378:metabolism / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors* / Q000502:physiology; D015854:Up-Regulation
chemical_list: D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; C495540:CAV1 protein, human; C493956:CDKN1A protein, human; D002352:Carrier Proteins; D051242:Caveolin 1; D022461:Caveolins; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D007334:Insulin-Like Growth Factor I; D004317:Doxorubicin; D017526:Receptor, IGF Type 1; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D048052:Mitogen-Activated Protein Kinase 3; D020169:Caspases