Nuclear localization of proteasome subunit beta 5 serves as an independent prognostic biomarker and promotes invasion in colorectal cancer

Figure 3 Proteasome subunit beta 5 is overexpressed and nuclear-enriched in metastatic colorectal cancer cell lines. A: Relative proteasome subunit beta 5 (PSMB5) mRNA levels in a panel of colorectal cancer cell lines compared to the normal colonic epithelial cell line FHC, determined by quantitative real-time polymerase chain reaction. Data are mean ± SD (n = 3). ^aP < 0.05 vs FHC, ^bP < 0.01 vs FHC, ^cP < 0.001 vs FHC; B: Western blot analysis of total PSMB5 protein in whole-cell lysates from the indicated cell lines. GAPDH serves as a loading control; C-E: Subcellular distribution of PSMB5 protein. Western blot analysis of PSMB5 in cytoplasmic and nuclear fractions extracted from the indicated cell lines, GAPDH and Lamin B1 serve as compartment-specific loading controls for cytoplasm and nucleus, respectively. Due to the limited number of lanes per gel, samples were analyzed across multiple independent blots (C); quantitative analysis of PSMB5 nuclear enrichment, nuclear-to-cytoplasmic ratio of PSMB5 in each cell line (D); percentage of total PSMB5 protein localized to the nucleus (E). Data are derived from densitometric analysis of three independent subcellular fractionation experiments and are presented as mean ± SD. ^aP < 0.05, ^bP < 0.01, ^cP < 0.001, CRC cell lines (RKO, SW620, SW480, LoVo, HT29, LS174T, HCT116) vs FHC. PSMB5: Proteasome subunit beta 5; GAPDH: Glyceraldehyde-3-phosphate dehydrogenase; C: Cytoplasmic; N: Nuclear.