Ubiquitin–Proteasome System Regulation of an Evolutionarily Conserved RNA Polymerase II-Associated Factor 1 Involved in Pancreatic Oncogenesis

Regulation of eukaryotic transcription initiation in response to cellular stress

Transcription initiation is a vital step in the regulation of eukaryotic gene expression. It can be dysregulated in response to various cellular stressors which is associated with numerous human diseases including cancer. Transcription initiation is facilitated via many gene-specific trans-regulatory elements such as transcription factors, activators, and coactivators through their interactions with transcription pre-initiation complex (PIC). These trans-regulatory elements can uniquely facilitate PIC formation (hence, transcription initiation) in response to cellular nutrient stress. Cellular nutrient stress also regulates the activity of other pathways such as target of rapamycin (TOR) pathway. TOR pathway exhibits distinct regulatory mechanisms of transcriptional activation in response to stress. Like TOR pathway, the cell cycle regulatory pathway is also found to be linked to transcriptional regulation in response to cellular stress. Several transcription factors such as p53, C/EBP Homologous Protein (CHOP), activating transcription factor 6 (ATF6α), E2F, transforming growth factor (TGF)-β, Adenomatous polyposis coli (APC), SMAD, and MYC have been implicated in regulation of transcription of target genes involved in cell cycle progression, apoptosis, and DNA damage repair pathways. Additionally, cellular metabolic and oxidative stressors have been found to regulate the activity of long non-coding RNAs (lncRNA). LncRNA regulates transcription by upregulating or downregulating the transcription regulatory proteins involved in metabolic and cell signaling pathways. Numerous human diseases, triggered by chronic cellular stressors, are associated with abnormal regulation of transcription. Hence, understanding these mechanisms would help unravel the molecular regulatory insights with potential therapeutic interventions. Therefore, here we emphasize the recent advances of regulation of eukaryotic transcription initiation in response to cellular stress.

Ubiquitin-proteasome system regulation of a key gene regulatory factor, Paf1C

Paf1 (Polymerase-associated factor 1) complex (Paf1C) is evolutionarily conserved from yeast to humans, and facilitates transcription elongation as well as co-transcriptional histone covalent modifications and mRNA 3'-end processing. Thus, Paf1C is a key player in regulation of eukaryotic gene expression. Paf1C consists of Paf1, Cdc73, Ctr9, Leo1 and Rtf1 in both yeast and humans, but it has an additional component, Ski8, in humans. The abundances of these components regulate the assembly of Paf1C and/or its functions, thus implying the mechanisms involved in regulating the abundances of the Paf1C components in altered gene expression and hence cellular pathologies. Towards finding the mechanisms associated with the abundances of the Paf1C components, we analyzed here whether the Paf1C components are regulated via targeted ubiquitylation and 26S proteasomal degradation. We find that the Paf1C components except Paf1 do not undergo the 26S proteasomal degradation in both yeast and humans. Paf1 is found to be regulated by the ubiquitin-proteasome system (UPS) in yeast and humans. Alteration of such regulation changes Paf1's abundance, leading to aberrant gene expression. Intriguingly, while the Rtf1 component of Paf1C does not undergo the 26S proteasomal degradation, it is found to be ubiquitylated, suggesting that Rtf1 ubiquitylation could be engaged in Paf1C assembly and/or functions. Collectively, our results reveal distinct UPS regulation of the Paf1C components, Paf1 and Rtf1, in a proteolysis-dependent and -independent manners, respectively, with functional implications.

A novel ubiquitin-proteasome system regulation of Sgf73/ataxin-7 that maintains the integrity of the coactivator SAGA in orchestrating transcription

Ataxin-7 maintains the integrity of Spt-Ada-Gcn5-Acetyltransferase (SAGA), an evolutionarily conserved coactivator in stimulating preinitiation complex (PIC) formation for transcription initiation, and thus, its upregulation or downregulation is associated with various diseases. However, it remains unknown how ataxin-7 is regulated that could provide new insights into disease pathogenesis and therapeutic interventions. Here, we show that ataxin-7's yeast homologue, Sgf73, undergoes ubiquitylation and proteasomal degradation. Impairment of such regulation increases Sgf73's abundance, which enhances recruitment of TATA box-binding protein (TBP) (that nucleates PIC formation) to the promoter but impairs transcription elongation. Further, decreased Sgf73 level reduces PIC formation and transcription. Thus, Sgf73 is fine-tuned by ubiquitin-proteasome system (UPS) in orchestrating transcription. Likewise, ataxin-7 undergoes ubiquitylation and proteasomal degradation, alteration of which changes ataxin-7's abundance that is associated with altered transcription and cellular pathologies/diseases. Collectively, our results unveil a novel UPS regulation of Sgf73/ataxin-7 for normal cellular health and implicate alteration of such regulation in diseases.

Design, Synthesis, and Biological Evaluation of 4-amino Substituted 2Hchromen- 2-one Derivatives as an NEDD8 Activating Enzyme Inhibitor in Pancreatic Cancer Cells

BACKGROUND

NEDD8 activating enzyme (NAE) plays a critical role in various cellular functions in carcinomas. The selective inhibition of NAE could mediate the rate of ubiquitination and the subsequent degradation of proteins associated with cancer so as to achieve the purpose of treatment.

OBJECTIVE

In this article, we decided to study the synthesis and screening of 4-amino substituted 2H-chromen-2-one derivatives against cancer cell lines, specifically the human pancreatic cancer cell line BxPC-3.

METHODS

After synthesis of twenty targeted compounds, we evaluated their anti-proliferative activity against six cancer cell lines, cytotoxicity against three normal cell lines through MTT assay, and hemolysis to screen out the candidate compound, which was further conducted drug-like physical property measurement, target confirmation by enzyme-based experiment, cell apoptosis, and synergistic effect research.

RESULTS

Starting from intermediates 4 and 5, several new 4-amino substituted 2H-chromen-2-one derivatives (9-28) were synthesized and evaluated for their cell activities using six cancer cell lines. We performed tests of cytotoxicity, hemolysis, ATP-dependent NAE inhibition in the enzyme- based system, apoptosis, and synergistic effect in BxPC-3 cells against the best candidate compound 21.

CONCLUSION

Based on these results, we found that compound 21 inhibited NAE activity in an ATP-dependent manner in the enzyme-based system, induced apoptosis in BxPC-3 cells, and synergized with bortezomib on BxPC-3 cell growth inhibition. Additionally, it had low toxicity with reasonable Log P-value and water solubility.

Synergistic anti-breast cancer effect of pulsatilla saponin D and camptothecin through interrupting autophagic-lysosomal function and promoting p62-mediated ubiquitinated protein aggregation

Autophagy is an evolutionarily conserved mechanism to protect the cells from unfavorable environmental conditions. Inhibition of autophagy has been contemplated as a novel strategy to enhance anticancer efficacy of existing chemotherapeutic agents. We previously reported that pulsatilla saponin D (PSD) was a potent autophagy inhibitor. However, its anticancer potential as adjuvant and underlying mechanisms are still unknown. In this study, we identified that PSD induced the formation of autophagosome in MCF-7 and MDA-MB-231 breast cancer cells. However, PSD alone and particularly co-treatment with camptothecin remarkably increased p62 protein levels, indicating that PSD strongly inhibited the autophagic cargo degradation. The mechanistic study indicated that PSD profoundly abolished the co-localization of EGFP-LC3 and lysosomal-specific probe LysoTracker Red, suggesting that the autophagosome-lysosome fusion was blocked by PSD, which is similar to the action of chloroquine. In addition, PSD significantly increased lysosomal pH and inhibited the activation of lysosomal cathepsins in both breast cancer cell lines. Furthermore, the accrued p62 resulted in accumulation of ubiquitinated proteins owing to the interaction with p62 and delivery to the malfunctioned autophagosome by PSD. Finally, we demonstrated that PSD synergistically enhanced the anticancer activity of camptothecin (CPT) in cultured breast cancer cells and in mouse xenograft tumor models. Our results indicated that PSD inhibited autophagic flux via blocking autophagosome-lysosome fusion and lysosomal acidification, which may confer a synergistic anti-breast cancer activity of PSD and CPT.

PSMC2 is Up-regulated in Pancreatic Cancer and Promotes Cancer Cell Proliferation and Inhibits Apoptosis

Objective: The lack of effective therapeutic targets poses a leading challenge to prolong survival and improve the quality of life for pancreatic cancer patients. Proteasome 26S subunit ATPase 2 (PSMC2), a recently discovered gene, has been implicated in certain human carcinogenesis. However, limited data is available concerning the functional significance of PSMC2 in cancer cell growth, and whether it plays a role in pancreatic carcinogenesis remains unknown.

Materials and Methods: Quantitative RT-PCR (qRT-PCR) was performed to assess mRNA expression levels of PSMC2 in different pancreatic cancer cell lines. Knockdown of PSMC2 was achieved by using short hairpin RNA (shRNA). The effects of PSMC2 silencing on pancreatic cancer cell proliferation and apoptosis were evaluated by the MTT cell proliferation assay, Celigoassays, Annexin V fluorescence-activated cell sorting (FACS) assay and Caspase-3/7 array.

Results: High expression of PSMC2 was detected in three pancreatic cancer cell lines (SW1990, PANC-1, and AsPC-1). Knockdown of PSMC2 in SW1990 cells inhibited proliferation and enhanced apoptosis.

Conclusions: Our primary study suggests that PSMC2 might be involved in the progression of pancreatic cancer and may serve as a potential therapeutic target.