Targeting RNA Polymerase I with Hernandonine Inhibits Ribosomal RNA Synthesis and Tumor Cell Growth

Hernandonine-mediated autophagic cell death in hepatocellular carcinoma: Interplay of p53 and YAP signaling pathways

Hepatocellular carcinoma (HCC), the primary form of liver cancer, is the third leading cause of cancer-related death globally. Hernandonine is a natural alkaloid derived from Hernandia nymphaeifolia that has been shown to exert various biological functions. In a previous study, hernandonine was shown to suppress the proliferation of several solid tumor cell lines without affecting normal human cell lines. However, little is known about the effect of hernandonine on HCC. Therefore, this study aimed to investigate the effect and mechanism of hernandonine on HCC in relation to autophagy. We found that hernandonine inhibited HCC cell growth in vitro and in vivo. In addition, hernandonine elicited autophagic cell death and DNA damage in HCC cells. RNA-seq analysis revealed that hernandonine upregulated p53 and Hippo signaling pathway-related genes in HCC cells. Small RNA interference of p53 resulted in hernandonine-induced autophagic cell death attenuation. However, inhibition of YAP sensitized HCC cells to hernandonine by increasing the autophagy induction. This is the first study to illustrate the complex involvement of p53 and YAP in the hernandonine-induced autophagic cell death in human HCC cells. Our findings provide novel evidence for the potential of hernandonine as a therapeutic agent for HCC treatment.

The nucleolus: Coordinating stress response and genomic stability

The perception that the nucleoli are merely the organelles where ribosome biogenesis occurs is challenged. Only around 30 % of nucleolar proteins are solely involved in producing ribosomes. Instead, the nucleolus plays a critical role in controlling protein trafficking during stress and, according to its dynamic nature, undergoes continuous protein exchange with nucleoplasm under various cellular stressors. Hence, the concept of nucleolar stress has evolved as cellular insults that disrupt the structure and function of the nucleolus. Considering the emerging role of this organelle in DNA repair and the fact that rDNAs are the most fragile genomic loci, therapies targeting the nucleoli are increasingly being developed. Besides, drugs that target ribosome synthesis and induce nucleolar stress can be used in cancer therapy. In contrast, agents that regulate nucleolar activity may be a potential treatment for neurodegeneration caused by abnormal protein accumulation in the nucleolus. Here, I explore the roles of nucleoli beyond their ribosomal functions, highlighting the factors triggering nucleolar stress and their impact on genomic stability.

Pyruvate kinase M2 modification by a lipid peroxidation byproduct acrolein contributes to kidney fibrosis

Renal fibrosis is a hallmark of diabetic nephropathy (DN) and is characterized by an epithelial-to-mesenchymal transition (EMT) program and aberrant glycolysis. The underlying mechanisms of renal fibrosis are still poorly understood, and existing treatments are only marginally effective. Therefore, it is crucial to comprehend the pathophysiological mechanisms behind the development of renal fibrosis and to generate novel therapeutic approaches. Acrolein, an α-,β-unsaturated aldehyde, is endogenously produced during lipid peroxidation. Acrolein shows high reactivity with proteins to form acrolein-protein conjugates (Acr-PCs), resulting in alterations in protein function. In previous research, we found elevated levels of Acr-PCs along with kidney injuries in high-fat diet-streptozotocin (HFD-STZ)-induced DN mice. This study used a proteomic approach with an anti-Acr-PC antibody followed by liquid chromatography–tandem mass spectrometry (LC–MS/MS) analysis to identify several acrolein-modified protein targets. Among these protein targets, pyruvate kinase M2 (PKM2) was found to be modified by acrolein at Cys358, leading to the inactivation of PKM2 contributing to the pathogenesis of renal fibrosis through HIF1α accumulation, aberrant glycolysis, and upregulation of EMT in HFD-STZ-induced DN mice. Finally, PKM2 activity and renal fibrosis in DN mice can be reduced by acrolein scavengers such as hydralazine and carnosine. These results imply that acrolein-modified PKM2 contributes to renal fibrosis in the pathogenesis of DN.

Targeting the nucleolus as a therapeutic strategy in human disease

The nucleolus is the site of ribosome biogenesis, one of the most resource-intensive processes in eukaryotic cells. Accordingly, nucleolar morphology and activity are highly responsive to growth signaling and nucleolar insults which are collectively included in the actively evolving concept of nucleolar stress. Importantly, nucleolar alterations are a prominent feature of multiple human pathologies, including cancer and neurodegeneration, as well as being associated with aging. The past decades have seen numerous attempts to isolate compounds targeting different facets of nucleolar activity. We provide an overview of therapeutic opportunities for targeting nucleoli in different pathologies and currently available therapies.

Regulation of RNA Polymerase I Stability and Function

RNA polymerase I is a highly processive enzyme with fast initiation and elongation rates. The structure of Pol I, with its in-built RNA cleavage ability and incorporation of subunits homologous to transcription factors, enables it to quickly and efficiently synthesize the enormous amount of rRNA required for ribosome biogenesis. Each step of Pol I transcription is carefully controlled. However, cancers have highjacked these control points to switch the enzyme, and its transcription, on permanently. While this provides an exceptional benefit to cancer cells, it also creates a potential cancer therapeutic vulnerability. We review the current research on the regulation of Pol I transcription, and we discuss chemical biology efforts to develop new targeted agents against this process. Lastly, we highlight challenges that have arisen from the introduction of agents with promiscuous mechanisms of action and provide examples of agents with specificity and selectivity against Pol I.

Acrolein plays a culprit role in the pathogenesis of diabetic nephropathy in vitro and in vivo

OBJECTIVE

Diabetic nephropathy (DN), also known as diabetic kidney disease (DKD), is a major chronic complication of diabetes and is the most frequent cause of kidney failure globally. A better understanding of the pathophysiology of DN would lead to the development of novel therapeutic options. Acrolein, an α,β-unsaturated aldehyde, is a common dietary and environmental pollutant.

DESIGN

The role of acrolein and the potential protective action of acrolein scavengers in DN were investigated using high-fat diet/ streptozotocin-induced DN mice and in vitro DN cellular models.

METHODS

Acrolein-protein conjugates (Acr-PCs) in kidney tissues were examined using immunohistochemistry. Renin-angiotensin system (RAS) and downstream signaling pathways were analyzed using quantitative RT-PCR and Western blot analyses. Acr-PCs in DN patients were analyzed using an established Acr-PC ELISA system.

RESULTS

We found an increase in Acr-PCs in kidney cells using in vivo and in vitro DN models. Hyperglycemia activated the RAS and downstream MAPK pathways, increasing inflammatory cytokines and cellular apoptosis in two human kidney cell lines (HK2 and HEK293). A similar effect was induced by acrolein. Furthermore, acrolein scavengers such as N-acetylcysteine, hydralazine, and carnosine could ameliorate diabetes-induced kidney injury. Clinically, we also found increased Acr-PCs in serum samples or kidney tissues of DKD patients compared to normal volunteers, and the Acr-PCs were negatively correlated with kidney function.

CONCLUSIONS

These results together suggest that acrolein plays a role in the pathogenesis of DN and could be a diagnostic marker and effective therapeutic target to ameliorate the development of DN.

Targeting Ribosome Biogenesis in Cancer: Lessons Learned and Way Forward

Simple Summary

Cells need to produce ribosomes to sustain continuous proliferation and expand in numbers, a feature that is even more prominent in uncontrollably proliferating cancer cells. Certain cancer cell types are expected to depend more on ribosome biogenesis based on their genetic background, and this potential vulnerability can be exploited in designing effective, targeted cancer therapies. This review provides information on anti-cancer molecules that target the ribosome biogenesis machinery and indicates avenues for future research.

Abstract

Rapid growth and unrestrained proliferation is a hallmark of many cancers. To accomplish this, cancer cells re-wire and increase their biosynthetic and metabolic activities, including ribosome biogenesis (RiBi), a complex, highly energy-consuming process. Several chemotherapeutic agents used in the clinic impair this process by interfering with the transcription of ribosomal RNA (rRNA) in the nucleolus through the blockade of RNA polymerase I or by limiting the nucleotide building blocks of RNA, thereby ultimately preventing the synthesis of new ribosomes. Perturbations in RiBi activate nucleolar stress response pathways, including those controlled by p53. While compounds such as actinomycin D and oxaliplatin effectively disrupt RiBi, there is an ongoing effort to improve the specificity further and find new potent RiBi-targeting compounds with improved pharmacological characteristics. A few recently identified inhibitors have also become popular as research tools, facilitating our advances in understanding RiBi. Here we provide a comprehensive overview of the various compounds targeting RiBi, their mechanism of action, and potential use in cancer therapy. We discuss screening strategies, drug repurposing, and common problems with compound specificity and mechanisms of action. Finally, emerging paths to discovery and avenues for the development of potential biomarkers predictive of therapeutic outcomes across cancer subtypes are also presented.

Cigarette smoke containing acrolein contributes to cisplatin resistance in human bladder cancers through the regulation of HER2 pathway or FGFR3 pathway

Cisplatin-based chemotherapy is the first-line therapy for bladder cancer (BC). However, cisplatin resistance has been associated with the recurrence of BC. Previous studies have shown that activation of fibroblast growth factor receptor (FGFR) and HER2 signaling are involved in BC cell proliferation and drug resistance. Smoking is the most common etiologic risk factor for BC, and there is emerging evidence that smoking is associated with cisplatin resistance. However, the underlying mechanism remains elusive. Acrolein, a highly reactive aldehyde, is abundant in tobacco smoke, cooking fumes, and automobile exhaust fumes. Our previous studies have shown that acrolein contributes to bladder carcinogenesis through the induction of DNA damage and inhibition of DNA repair. In this study, we found that acrolein induced cisplatin resistance and tumor progression in both non-muscle invasive BC (NMIBC) and muscle invasive BC (MIBC) cell lines RT4 and T24, respectively. Activation of HER2 and FGFR3 signaling contributes to acrolein-induced cisplatin resistance in RT4 and T24 cells, respectively. Furthermore, trastuzumab, an anti-HER2 antibody, and PD173074, a FGFR inhibitor, reversed cisplatin resistance in RT4 and T24 cells, respectively. Using a xenograft mouse model with acrolein-induced cisplatin-resistant T24 clones, we found that cisplatin combined with PD173074 significantly reduced tumor size compared to cisplatin alone. These results indicate that differential molecular alterations behind cisplatin resistance in NMIBC and MIBC significantly alter the effectiveness of targeted therapy combined with chemotherapy. This study provides valuable insights into therapeutic strategies for cisplatin-resistant bladder cancer.

Cigarette Smoke Containing Acrolein Upregulates EGFR Signaling Contributing to Oral Tumorigenesis In Vitro and In Vivo

Oral squamous cell carcinoma (OSCC) accounts for 80-90% of all intraoral malignant neoplasms. The single greatest risk factor for oral cancer is tobacco use, including cigarettes, cigars, chewing tobacco, and snuff. Aberrations of the epidermal growth factor receptor (EGFR) pathway features prominently in oral tumorigenesis and progression. It was shown that cigarette smoking (CS) is associated with worse prognosis in OSCC patients and overexpression of EGFR in tumor tissue. However, the mechanism by which cigarette smoking induced EGFR pathway activation remains to be fully elucidated. Acrolein, an IARC group 2A carcinogen, is a highly reactive aldehyde found in CS. Here we report that acrolein is capable of inducing tumorigenic transformation in normal human oral keratinocytes (NOK). The acrolein-transformed NOK cells showed EGFR copy number amplification, increased EGFR expression, and activation of downstream ERK and AKT signaling pathway. No p53 mutations were observed in acrolein-transformed NOK cells. Inhibiting EGFR pathway using an anti-EGFR antibody, cetuximab, inhibits tumor growth. Furthermore, by examining tissue sample from patients, we found an increased EGFR copy number was positively associated with acrolein-induced DNA damages in OSCC patients. Taken together, our results indicate that acrolein is important in tumorigenic transformation through amplification of EGFR and activating the downstream signaling pathway, contributing to oral carcinogenesis. This is the first study to provide molecular evidence showing that CS containing acrolein contributes to EGFR amplification in OSCC.

Sempervirine inhibits RNA polymerase I transcription independently from p53 in tumor cells

In the search of small molecules that can target MDM2/p53 pathway in testicular germ cell tumors (TGCTs), we identified sempervirine (2,3,4,13-tetrahydro-1H-benz[g]indolo[2,3-a]quinolizin-6-ium), an alkaloid of Gelsemium sempervirens, that has been previously proposed as an inhibitor of MDM2 that targets p53-wildtype (wt) tumor cells. We found that sempervirine not only affects cell growth of p53-wt cancer cells, but it is also active in p53-mutated and p53-null cells by triggering p53-dependent and independent pathways without affecting non-transformed cells. To understand which mechanism/s could be activated both in p53-wt and -null cells, we found that sempervirine induced nucleolar remodeling and nucleolar stress by reducing protein stability of RPA194, the catalytic subunit of RNA polymerase I, that led to rRNA synthesis inhibition and to MDM2 block. As shown for other cancer cell models, MDM2 inhibition by nucleolar stress downregulated E2F1 protein levels both in p53-wt and p53-null TGCT cells with the concomitant upregulation of unphosphorylated pRb. Finally, we show that sempervirine is able to enter the nucleus and accumulates within the nucleolus where it binds rRNA without causing DNA damage. Our results identify semperivirine as a novel rRNA synthesis inhibitor and indicate this drug as a non-genotoxic anticancer small molecule.

The p53 family reaches the final frontier: the variegated regulation of the dark matter of the genome by the p53 family in cancer

The tumour suppressor p53 and its paralogues, p63 and p73, are essential to maintain cellular homoeostasis and the integrity of the cell's genetic material, thus meriting the title of 'guardians of the genome'. The p53 family members are transcription factors and fulfill their activities by controlling the expression of protein-coding and non-coding genes. Here, we review how the latter group transcended from the 'dark matter' of the transcriptome, providing unexpected and intriguing anti-cancer therapeutic strategies.