[en] Gene expression is regulated at multiple steps, such as transcription, splicing, export, degradation and translation. Considering diverse roles of SR proteins, we determined whether the tumor-related splicing factor SRSF3 regulates the expression of the tumor-suppressor protein, PDCD4, at multiple steps. As we have reported previously, knockdown of SRSF3 increased the PDCD4 protein level in SW480 colon cancer cells. More interestingly, here we showed that the alternative splicing and the nuclear export of minor isoforms of pdcd4 mRNA were repressed by SRSF3, but the translation step was unaffected. In contrast, only the translation step of the major isoform of pdcd4 mRNA was repressed by SRSF3. Therefore, overexpression of SRSF3 might be relevant to the repression of all isoforms of PDCD4 protein levels in most types of cancer cell. We propose that SRSF3 could act as a coordinator of the expression of PDCD4 protein via two mechanisms on two alternatively spliced mRNA isoforms.

[en] Highlights: • Wnt signaling as well as β-catenin overexpression enhance HuR cytoplasmic export. • HuR overexpression promotes cytoplasmic localization of β-catenin from the perinuclear fraction. • Wnt/β-catenin-mediated transcriptional activity is repressesed by HuR. - Abstract: β-Catenin is the key transcriptional activator of canonical Wnt signaling in the nucleus; thus, nuclear accumulation of β-catenin is a critical step for expressing target genes. β-Catenin accumulates in the nucleus of cancer cells where it activates oncogenic target genes. Hu antigen R (HuR) is a RNA binding protein that regulates multiple post-transcriptional processes including RNA stability. Thus, cytoplasmic HuR protein may be involved in tumorigenesis by stabilizing oncogenic transcripts, but the molecular mechanism remains unclear. Here, we observed that Wnt/β-catenin signaling induced export of the HuR protein, whereas HuR overexpression promoted accumulation of the β-catenin protein in the cytoplasm. Thus, Wnt/β-catenin-mediated transcriptional activity in the nucleus was reduced by overexpressing HuR. These results suggest novel and uncharacterized cytoplasmic β-catenin functions related to HuR-mediated RNA metabolism in cancer cells

[en] Research highlights: → Cyclin D1 transcription is directly activated by β-catenin; however, β-catenin-induced cyclin D1 transcription is reduced by NF-κB p65. → Protein-protein interaction between NF-κB p65 and β-catenin might be responsible for p65-mediated repression of cyclin D1. → One of five putative binding sites, located further upstream of other sites, is the major β-catenin binding site in the cyclin D1 promoter. → NF-κB binding site in cyclin D1 is occupied not only by p65 but also by β-catenin, which is dynamically regulated by the signal. -- Abstract: Signaling crosstalk between the β-catenin and NF-κB pathways represents a functional network. To test whether the crosstalk also occurs on their common target genes, the cyclin D1 promoter was used as a model because it contains binding sites for both proteins. β-catenin activated transcription from the cyclin D1 promoter, while co-expression of NF-κB p65 reduced β-catenin-induced transcription. Chromatin immunoprecipitation revealed lithium chloride-induced binding of β-catenin on one of the T-cell activating factor binding sites. More interestingly, β-catenin binding was greatly reduced by NF-κB p65, possibly by the protein-protein interaction between the two proteins. Such a dynamic and complex binding of β-catenin and NF-κB on promoters might contribute to the regulated expression of their target genes.

[en] Imaging biomarkers from functional imaging modalities were assessed as potential surrogate markers of disease status. Specifically, in this prospective study, we investigated the relationships between functional imaging parameters and histological prognostic factors and breast cancer subtypes. In total, 43 patients with large or locally advanced invasive ductal carcinoma (IDC) were analyzed (47.6 ± 7.5 years old). ⁶⁸Ga-Labeled arginine-glycine-aspartic acid (RGD) and ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) were performed. The maximum and average standardized uptake values (SUV_max and SUV_avg) from RGD PET/CT and SUV_max and SUV_avg from FDG PET/CT were the imaging parameters used. For histological prognostic factors, estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) expression was identified using immunohistochemistry (IHC) or fluorescent in situ hybridization (FISH). Four breast cancer subtypes, based on ER/PR and HER2 expression (ER/PR+,Her2-, ER/PR+,Her2+, ER/PR-,Her2+, and ER/PR-,Her2-), were considered. Quantitative FDG PET parameters were significantly higher in the ER-negative group (15.88 ± 8.73 vs 10.48 ± 6.01, p = 0.02 for SUV_max; 9.40 ± 5.19 vs 5.92 ± 4.09, p = 0.02 for SUV_avg) and the PR-negative group (8.37 ± 4.94 vs 4.79 ± 3.93, p = 0.03 for SUV_avg). Quantitative RGD PET parameters were significantly higher in the HER2-positive group (2.42 ± 0.59 vs 2.90 ± 0.75, p = 0.04 for SUV_max; 1.60 ± 0.38 vs 1.95 ± 0.53, p = 0.04 for SUV_avg) and showed a significant positive correlation with the HER2/CEP17 ratio (r = 0.38, p = 0.03 for SUV_max and r = 0.46, p < 0.01 for SUV_avg). FDG PET parameters showed significantly higher values in the ER/PR-,Her2- subgroup versus the ER/PR+,Her2- or ER/PR+,Her2+ subgroups, while RGD PET parameters showed significantly lower values in the ER/PR-,Her2- subgroup versus the other subgroups. There was no correlation between FDG and RGD PET parameters in the overall group. Only the ER/PR-,Her2- subgroup showed a significant positive correlation between FDG and RGD PET parameters (r = 0.59, p = 0.03 for SUV_max). ⁶⁸Ga-RGD and ¹⁸F-FDG PET/CT are promising functional imaging modalities for predicting biomarkers and molecular phenotypes in breast cancer patients. (orig.)