Inhibitory effect of ubiquitin-proteasome pathway on proliferation of esophageal carcinoma cells

Evaluation of the NRF1-proteasome axis as a therapeutic target in breast cancer

Proteasomes are multi-subunit complexes that specialize in protein degradation. Cancer cells exhibit a heightened dependence on proteasome activity, presumably to support their enhanced proliferation and other cancer-related characteristics. Here, a systematic analysis of TCGA breast cancer datasets revealed that proteasome subunit transcript levels are elevated in all intrinsic subtypes (luminal, HER2-enriched, and basal-like/triple-negative) when compared to normal breast tissue. Although these observations suggest a pan-breast cancer utility for proteasome inhibitors, our further experiments with breast cancer cell lines and patient-derived xenografts (PDX) pointed to triple-negative breast cancer (TNBC) as the most sensitive subtype to proteasome inhibition. Finally, using TNBC cells, we extended our studies to in vivo xenograft experiments. Our previous work has firmly established a cytoprotective role for the transcription factor NRF1 via its ability to upregulate proteasome genes in response to proteasome inhibition. In further support of this notion, we show here that NRF1 depletion significantly reduced tumor burden in an MDA-MB-231 TNBC xenograft mouse model treated with carfilzomib. Taken together, our results point to TNBC as a particularly vulnerable breast cancer subtype to proteasome inhibition and provide a proof-of-principle for targeting NRF1 as a viable means to increase the efficacy of proteasome inhibitors in TNBC tumors.

Protein clearance strategies for disease intervention

Protein homeostasis, or proteostasis, is essential for cell function and viability. Unwanted, damaged, misfolded and aggregated proteins are degraded by the ubiquitin–proteasome system (UPS) and the autophagy-lysosome pathway. Growing evidence indicates that alterations in these major proteolytic mechanisms lead to a demise in proteostasis, contributing to the onset and development of distinct diseases. Indeed, dysregulation of the UPS or autophagy is linked to several neurodegenerative, infectious and inflammatory disorders as well as cancer. Thus, modulation of protein clearance pathways is a promising approach for therapeutics. In this review, we discuss recent findings and open questions on how targeting proteolytic mechanisms could be applied for disease intervention.

Cancer Stem-like Properties in Colorectal Cancer Cells with Low Proteasome Activity

PURPOSE

One of the main reasons for cancer treatment resistance is the existence of cancer stem-like cells (CSCs). Here, we elucidated the relationship between low proteasome activity cells (LPACs) and CSCs.

EXPERIMENTAL DESIGN

The human colorectal cancer cell lines HCT116, SW480, DLD1, and KM12SM were engineered to stably express a green fluorescent molecule fused to the degron of ornithine decarboxylase, resulting in an accumulation of the fluorescence in LPACs. LPACs were isolated by flow cytometry. Treatment resistance (radio- and chemotherapy) and the capacity of LPACs to act as CSCs were analyzed. Microarray analysis was performed to reveal genes related to treatment resistance. The prognostic impact of potent genes was examined in 190 patients with colorectal cancer.

RESULTS

LPACs had a significantly increased capacity for radioresistance and chemoresistance (5-fluorouracil and oxaliplatin), significantly lower reactive oxygen species activity, and significantly increased sphere formation capacity compared with non-LPACs. The number of cells in the G0-G1 phase was significantly higher among LPACs. Subcutaneous injection of as few as 20 LPACs led to tumor formation in immunologically incompetent mice. Microarray analysis revealed that the expression of EP300-interacting inhibitor of differentiation 3 (EID3) was significantly increased in LPACs. In vitro assay revealed that EID3 positively controlled cell proliferation and treatment resistance. The high expression of EID3 was an adverse prognostic indicator in patients with colorectal cancer (P = 0.0400).

CONCLUSIONS

LPACs have characteristic treatment resistance and act as CSCs in colorectal cancer. In addition, EID3 is one of the potential regulators of treatment resistance in colorectal cancer and may be a potential therapeutic target. Clin Cancer Res; 22(21); 5277-86. ©2016 AACR.

Identifying reproducible cancer-associated highly expressed genes with important functional significances using multiple datasets

Identifying differentially expressed (DE) genes between cancer and normal tissues is of basic importance for studying cancer mechanisms. However, current methods, such as the commonly used Significance Analysis of Microarrays (SAM), are biased to genes with low expression levels. Recently, we proposed an algorithm, named the pairwise difference (PD) algorithm, to identify highly expressed DE genes based on reproducibility evaluation of top-ranked expression differences between paired technical replicates of cells under two experimental conditions. In this study, we extended the application of the algorithm to the identification of DE genes between two types of tissue samples (biological replicates) based on several independent datasets or sub-datasets of a dataset, by constructing multiple paired average gene expression profiles for the two types of samples. Using multiple datasets for lung and esophageal cancers, we demonstrated that PD could identify many DE genes highly expressed in both cancer and normal tissues that tended to be missed by the commonly used SAM. These highly expressed DE genes, including many housekeeping genes, were significantly enriched in many conservative pathways, such as ribosome, proteasome, phagosome and TNF signaling pathways with important functional significances in oncogenesis.

The Mechanistic Links Between Proteasome Activity, Aging and Age-related Diseases

Damaged and misfolded proteins accumulate during the aging process, impairing cell function and tissue homeostasis. These perturbations to protein homeostasis (proteostasis) are hallmarks of age-related neurodegenerative disorders such as Alzheimer’s, Parkinson’s or Huntington’s disease. Damaged proteins are degraded by cellular clearance mechanisms such as the proteasome, a key component of the proteostasis network. Proteasome activity declines during aging, and proteasomal dysfunction is associated with late-onset disorders. Modulation of proteasome activity extends lifespan and protects organisms from symptoms associated with proteostasis disorders. Here we review the links between proteasome activity, aging and neurodegeneration. Additionally, strategies to modulate proteasome activity and delay the onset of diseases associated to proteasomal dysfunction are discussed herein.

Roles of estrogen receptor and p21(Waf1) in bortezomib-induced growth inhibition in human breast cancer cells

Proteasome inhibitors such as bortezomib constitute novel therapeutic agents that are currently in clinical use and in clinical trials. In some neoplasms, cyclin-dependent kinase inhibitors (CKI) such as p21(WAF1) have been proposed as key targets of proteasome inhibitors. p21(WAF1) expression can be modulated by p53, a tumor suppressor, and especially in breast cancer cells, by estrogen receptor alpha (ERα), which is highly relevant to cancer growth. We investigated the effects of bortezomib using a panel of six cancer cell lines with variable status of ERα or p53 and found that bortezomib inhibited the growth of all cell lines in the same concentration range irrespective of the ERα expression or the mutational status of p53. Bortezomib treatment significantly enhanced p21(WAF1) protein levels in all cell lines but with different mechanisms according to ERα status. In ERα-positive cells, bortezomib treatment caused a strong increase in p21(WAF1) mRNA, whereas in ERα-negative cells it predominantly enhanced p21(WAF1) protein levels suggesting a posttranslational mechanism of p21(WAF1) regulation in the ERα-negative cells. Moreover, the antiproliferative activity of bortezomib was prevented by ERα silencing or p21(WAF1) knockdown in ERα-positive cells. Collectively, our results highlight the potential roles of ERα and p21(WAF1) in growth inhibition of cancer cells mediated by proteasome inhibitors, such as bortezomib.

Analysis of transcriptional factors and regulation networks in laryngeal squamous cell carcinoma patients with lymph node metastasis

The present study was to identify and quantitate differentially expressed proteins in laryngeal squamous cell carcinoma (LSCC) tissues with or without lymph node metastasis and to explore transcriptional factors and regulation networks associated with the process. Tissue specimens were taken from 20 patients with LSCC, including 10 cases of LSCC without metastasis LSCC (N0) and 10 cases of LSCC with metastasis LSCC (Nx). Among the 643 unique proteins identified by using iTRAQ labeling and quantitative proteomic technology, 389 proteins showed an abundance change in LSCC (Nx) as compared to LSCC (N0). Cytoskeleton remodeling, cell adhesion, and immune response activation were found to be the main processes in LSCC metastasis. The construction of transcription regulation networks identified key transcription regulators for lymph node metastasis of LSCC, including Sp1, c-myc, and p53, which may affect LSCC metastasis through the epithelial-mesenchymal transition. Furthermore, our results suggest that ubiquitination may be a critical factor in the networks. The present study provides insights into transcriptional factors and regulation networks involved in LSCC metastasis, which may lead to new strategies for treatment of LSCC metastasis.

Effect of p27mt gene on apoptosis of the colorectal cancer cell line Lovo

AIM: To construct p27mt recombinant adenovirus, transfect the colorectal cell line Lovo and observe the effects of p27mt on Lovo cell apoptosis and cell cycle inhibition.

METHODS: We constructed recombinant adenovirus containing p27mt by homologous recombination in bacteria. The colorectal cancer cell line Lovo was infected with recombinant replication-defective adenovirus Ad-p27mt, and expression of p27mt was determined by Western blotting; the inhibitory effect of p27mt on Lovo cells was detected by cytometry. Cell cycle was determined by flow cytometry. DNA fragment analysis identified the occurrence of apoptosis.

RESULTS: The recombinant adenovirus which already contained p27mt target gene was successfully constructed. When multiplicity of infection was ≥ 50, the infection efficiency was 100%. After transfection of Lovo cells with Ad-p27mt the cells had high p27 expression which was identified by immunoblotting assay. PI staining and flow cytometry showed that 77.96% of colorectal cancer cells were inhibited in phase G₀/G₁, while in the Ad-LacZ group and blank control group, 27.57% and 25.29% cells were inhibited in the same phase, respectively. DNA fragment analysis, flow cytometry and TUNEL assay demonstrated that p27mt is able to induce apoptosis in colorectal cancer cells.

CONCLUSION: p27mt has an obvious blocking effect on colorectal cancer cell cycle, and most cells were inhibited in phase G₀/G₁. Therefore, p27mt can induce apoptosis in colorectal cells.

Increased proteasome activity, ubiquitin-conjugating enzymes, and eEF1A translation factor detected in breast cancer tissue

The ubiquitin (Ub)/proteasome pathway facilitates the degradation of damaged proteins and regulators of growth and stress response. The activation of this pathway in various cancers and malignancies has been described, and several genetic determinants of breast cancer, including BRCA1 and BRCA2, are linked to protein degradation. To investigate the involvement of the Ub/proteasome system in breast cancer, we examined a collection of 25 patient-matched breast cancer and normal adjacent tissues and detected activation of numerous components of the Ub/proteasome pathway. The activity of the proteasome, and levels of proteasome subunits and various targeting factors, were increased in >90% of primary breast cancer tissue specimens. In contrast, no activation was observed in benign solid tumors, indicating that the response is specific to abnormal growth in neoplastic cells. Additionally, the accumulation of high levels of certain Ub-conjugating enzymes (UbcH1, UbcH2, and UbcH5), was specific to breast cancer, as no change in abundance was detected in primary colon cancer tissue extracts. Surprisingly, the Ub/proteasome system was not activated in a well-characterized cell culture-based breast cancer model system. Collectively, these findings suggest that the analysis of primary breast cancer tissue samples will be indispensable for the biochemical characterization of neoplastic growth and for the development of therapeutics.