Metastasis: Resistance fighters

CDC20 and PTTG1 are Important Biomarkers and Potential Therapeutic Targets for Metastatic Prostate Cancer

INTRODUCTION

Metastatic prostate cancer (mPCa) is responsible for most prostate cancer (PCa) deaths worldwide. The present study aims to explore the molecular differences between mPCa and PCa.

METHODS

The authors downloaded GSE6752, GSE6919, and GSE32269 from the Gene Expression Omnibus and employed integrated analysis to identify differentially expressed genes (DEGs) between mPCa and PCa. Functional and pathway-enrichment analyses were performed, and a protein-protein interaction (PPI) network and modules were constructed. Clinical mPCa specimens were collected to verify the results by performing RT-qPCR. The Cancer Genome Atlas database was used to conduct a survival analysis, and an immunohistochemical assay was performed. The invasion ability of PCa cells was verified by Transwell assay.

RESULTS

One-hundred six consistently DEGs were found in mPCa compared with PCa. DEGs significantly enriched the positive regulation of cell proliferation, cell division, and cell adhesion in small cell lung cancer and PCa. Cell division, nucleoplasm, and cell cycle were selected from the PPI network, and the top 10 hub genes were selected. CDC20 and PTTG1 with genetic alterations were significantly associated with poorer disease-free survival. Immunohistochemical assay results showed that the expression levels of CDC20 and PTTG1 in mPCa were higher than those in PCa. The results of the migration assay indicated that CDC20 and PTTG1 could enhance the migration ability of PCa cells.

CONCLUSION

The present study revealed that CDC20 and PTTG1 contribute more to migration, progression, and poorer prognoses in mPCa compared with PCa. CDC20 and PTTG1 could represent therapeutic targets in mPCa medical research and clinical studies.

Secretome profiling of PC3/nKR cells, a novel highly migrating prostate cancer subline derived from PC3 cells

Prostate cancer (PCa) is the most common cancer among men worldwide. Most PCa cases are not fatal; however, the outlook is poor when PCa spreads to another organ. Bone is the target organ in about 80% of patients who experience metastasis from a primary PCa tumor. In the present study, we characterized the secretome of PC3/nKR cells, which are a new subline of PC3 cells that were originally isolated from nude mice that were implanted with PC3 cells without anti-natural killer (NK) cell treatment. Wound healing and Transwell assays revealed that PC3/nKR cells had increased migratory and invasive activities in addition to a higher resistance to NK cells-induced cytotoxicity as compared to PC3 cells. We quantitatively profiled the secreted proteins of PC3/nKR and PC3 cells by liquid chromatography-tandem mass spectrometry analysis coupled with 2-plex tandem mass tag labeling. In total, 598 secretory proteins were identified, and 561 proteins were quantified, among which 45 proteins were secreted more and 40 proteins were secreted less by PC3/nKR cells than by PC3 cells. For validation, the adapter molecule crk, serpin B3, and cystatin-M were analyzed by western blotting. PC3/nKR cells showed the selective secretion of NKG2D ligand 2, HLA-A, and IL-6, which may contribute to their NK cell-mediated cytotoxicity resistance, and had a high secretion of crk protein, which may contribute to their high migration and invasion properties. Based on our secretome analysis, we propose that PC3/nKR cells represent a new cell system for studying the metastasis and progression of PCa.

Mechanism underlying the retarded nuclear translocation of androgen receptor splice variants

As shown in our previous study, two alternatively spliced androgen receptor (AR) variants, which are exclusively expressed in the granulosa cells of patients with polycystic ovary syndrome, exhibit retarded nuclear translocation compared with wild-type AR. However, researchers have not yet determined whether these abnormalities correlate with heat shock protein 90 (HSP90) and importin α (the former is a generally accepted co-chaperone of AR, and the latter is a component of classical nuclear import complexes). Here, these two variants were mainly retained in cytoplasm with HSP90 and importin α in the presence of dihydrotestosterone (DHT), and their levels in nucleus were significantly reduced, according to the immunofluorescence staining. The binding affinity of two AR variants for importin α was consistently decreased, while it was increased in WT-AR following DHT stimulation, leading to reduced nuclear import, particularly for the insertion-AR (Ins-AR). However, the binding affinities of two AR variants for HSP90 were increased in the absence of DHT compared with WT-AR, which functioned to maintain spatial structural stability, particularly for the deletion-AR (Del-AR). Therefore, the retarded nuclear translocation of two AR variants is associated with HSP90 and importin α, and the abnormal binding affinities for them play critical roles in this process.

RNA splicing and splicing regulator changes in prostate cancer pathology

Changes in mRNA splice patterns have been associated with key pathological mechanisms in prostate cancer progression. The androgen receptor (abbreviated AR) transcription factor is a major driver of prostate cancer pathology and activated by androgen steroid hormones. Selection of alternative promoters by the activated AR can critically alter gene function by switching mRNA isoform production, including creating a pro-oncogenic isoform of the normally tumour suppressor gene TSC2. A number of androgen-regulated genes generate alternatively spliced mRNA isoforms, including a prostate-specific splice isoform of ST6GALNAC1 mRNA. ST6GALNAC1 encodes a sialyltransferase that catalyses the synthesis of the cancer-associated sTn antigen important for cell mobility. Genetic rearrangements occurring early in prostate cancer development place ERG oncogene expression under the control of the androgen-regulated TMPRSS2 promoter to hijack cell behaviour. This TMPRSS2-ERG fusion gene shows different patterns of alternative splicing in invasive versus localised prostate cancer. Alternative AR mRNA isoforms play a key role in the generation of prostate cancer drug resistance, by providing a mechanism through which prostate cancer cells can grow in limited serum androgen concentrations. A number of splicing regulator proteins change expression patterns in prostate cancer and may help drive key stages of disease progression. Up-regulation of SRRM4 establishes neuronal splicing patterns in neuroendocrine prostate cancer. The splicing regulators Sam68 and Tra2β increase expression in prostate cancer. The SR protein kinase SRPK1 that modulates the activity of SR proteins is up-regulated in prostate cancer and has already given encouraging results as a potential therapeutic target in mouse models.

Exo70 is an independent prognostic factor in colon cancer

Exo70, a key component of the Exocyst complex, plays important roles in human cancer progression beyond exocytosis. However, the expression of Exo70 and its prognostic value for patients with colon cancer has not been well investigated to date. In this study, we observed that the mRNA and protein levels of Exo70 were upregulated in 11 of 13 colon cancer tissues, compared with their normal counterparts, which was validated by immunohistochemical analysis in a tissue microarray containing 89 pairs of colon cancer tissues and the matched adjacent normal tissues. Statistical analysis revealed that Exo70 expression is positively correlated with tumor size, invasion depth, TNM stage and distant metastasis. Kaplan-Meier survival analysis showed that colon cancer patients with higher Exo70 expression have a poorer clinical outcome than those with lower Exo70 expression. Multivariate Cox regression analysis revealed that Exo70, age and distant metastasis were there independent prognostic factors for overall survival rate of colon cancer patients. Through gain- and loss of Exo70 in colon cancer cells, we found that Exo70 could enhance the migration ability of colon cancer cells. Taken together, our studies revealed that Exo70 might be a promising negative prognostic factor and a potential therapeutic target for colon cancer.