Expression of caveolin-1 is up-regulated in prostate cancer metastasis and is associated with aggressive recurrence of the disease. Intriguingly, caveolin-1 is also secreted from prostate cancer cell lines and has been identified in secreted prostasomes. Caveolin-1 is the major structural component of the plasma membrane invaginations called caveolae. Co-expression of the coat protein Polymerase I and transcript release factor (PTRF) is required for caveolae formation. We recently found that expression of caveolin-1 in the aggressive prostate cancer cell line PC-3 is not accompanied by PTRF, leading to noncaveolar caveolin-1 lipid rafts. Moreover, ectopic expression of PTRF in PC-3 cells sequesters caveolin-1 into caveolae. Here we quantitatively analyzed the effect of PTRF expression on the PC-3 proteome using stable isotope labeling by amino acids in culture and subcellular proteomics. We show that PTRF reduced the secretion of a subset of proteins including secreted proteases, cytokines, and growth regulatory proteins, partly via a reduction in prostasome secretion. To determine the cellular mechanism accounting for the observed reduction in secreted proteins we analyzed total membrane and the detergent-resistant membrane fractions. Our data show that PTRF expression selectively impaired the recruitment of actin cytoskeletal proteins to the detergentresistant membrane, which correlated with altered cholesterol distribution in PC-3 cells expressing PTRF. Consistent with this, modulating cellular cholesterol altered the actin cytoskeleton and protein secretion in PC-3 cells. Intriguingly, several proteins that function in ER to Golgi trafficking were reduced by PTRF expression. Taken together, these results suggest that the noncaveolar caveolin-1 found in prostate cancer cells generates a lipid raft microenvironment that accentuates secretion pathways, possibly at the step of ER sorting/exit. Importantly, these effects could be modulated by PTRF expression. Molecular & Cellular Proteomics 11: 10.1074/mcp.M111.012245, 1-13, 2012.Prostate cancer is the most commonly diagnosed cancer in men and the second leading cause of cancer related deaths in developed countries. Although localized prostate cancer is treatable, metastatic recurrence, together with development of androgen-independence, leads to advanced prostate cancer, which currently has a low survival rate. Caveolin-1, a cholesterol-binding integral membrane protein, has been shown to be up-regulated in prostate cancer metastasis and is associated with androgen-independence and aggressive recurrence of the disease (1). A prostate cancer mouse model showed that genetic ablation of caveolin-1 delays the onset of advanced prostate cancer (2), underscoring its importance in prostate cancer progression. Hence understanding caveolin-1 action in prostate cancer progression is crucial for the design of novel intervention strategies to manage this devastating disease.Caveolin-1 is a major structural component of caveolae, specialized lipid raft microdomains of the pl...

Background: Galectin-3-N-glycan binding forms a lattice that regulates cancer cell adhesion, migration, and signaling. Results: Galectin-3 destabilizes cell-cell junctions and increases junctional mobility of N-cadherin and GM1 ganglioside. Conclusion: Galectin-3 is a novel regulator of N-cadherin dynamics and cell-cell junction stability. Significance: First demonstration of galectin-3 regulation of both glycoprotein and glycolipid mobility defines novel roles for the galectin lattice in junctional stability.

Lipid rafts are membrane microdomains involved in many cellular functions, including transduction of cellular signals and cell entry by pathogens. Lipid rafts can be enriched biochemically by extraction in a nonionic detergent at low temperature, followed by floatation on a sucrose density gradient. Previous proteomic studies of such detergentresistant membranes (DRMs) are in disagreement about the presence of mitochondrial proteins in raft components. Here, we approach the status of mitochondrial proteins in DRM preparations by employing stable isotope labeling by amino acids in cell culture to evaluate the composition of differentially purified subcellular fractions as well as highresolution linear density gradients. Our data demonstrate that F 1 /F 0 ATPase subunits, voltage-dependent anion selective channels, and other mitochondrial proteins are at best partially copurifying contaminants of raft preparations.

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