Poly r(C) Binding Protein-1 is Central to Maintenance of Cancer Stem Cells in Prostate Cancer Cells

Aims: To investigate global proteomic changes induced in CD44+CD24-stem cells isolated from the prostate cancer cell lines, LNCaP and DU145, post prolonged TGF-beta treatment in order to understand underlying mechanisms that promote stemness in prostate cancer cells. Methods: CD44+CD133+alpha 2 beta 1Integrin+CD24-population was isolated from mock or TGF-beta treated (7 days) prostate cancer cell line, LNCaP, through fluorescent activated cell sorting. Cell lysates were obtained from the +/- TGF-beta cell population and proteomics profiling (MS/MS) was performed by mass spectrometry. Relative enrichment or depletion in the CD44+CD24-population post-TGF-beta treatment was determined relative to mock-treated CD44+CD24-cells post normalization to GAPDH expression levels. Results obtained from MS/MS were validated using immunoblotting. Functional validation of one putative regulator was performed using gain-of-function strategy to investigate its role in rendering stemness in LNCaP and DU145 cells in vitro and in promoting tumorigenicity in vivo. Results: TGF-beta treatment caused significant enrichment of CD44+CD24-population in LNCaP cells (22.35 +/- 0.94% in mock treated vs 95.23 +/- 2.34% in TGF-beta treated cells; P < 0.01), which were also positive for CD133 and alpha 2 beta 1Integrin. Mass spectrometry analysis of the enriched cell population revealed that sixty-three proteins were either up-or down-regulated greater than five folds, out of which the poly r(C) binding protein (PCBP)-1 was the most down-regulated (9.31 +/- 0.05 folds). Ectopic overexpression of PCBP1 in LNCaP and DU145 cells not only attenuated enrichment of CD44+CD133+CD24-population in these cells following TGF-beta treatment, but also significantly decreased tumorigenicity of the stem cell subset, as assessed by in vitro soft agar colony formation and in vivo xenograft assays. Conclusion: Our proteomic profiling and subsequent validation indicate that PCBP1 is central to CSCs enrichment and functionality in prostate cancer. Copyright (C) 2015 S. Karger AG, Basel