Post-Translational Regulation of ARF: Perspective in Cancer

Tumorigenesis can be induced by various stresses that cause aberrant DNA mutations and unhindered cell proliferation. Under such conditions, normal cells autonomously induce defense mechanisms, thereby stimulating tumor suppressor activation. ARF, encoded by the CDKN2a locus, is one of the most frequently mutated or deleted tumor suppressors in human cancer. The safeguard roles of ARF in tumorigenesis are mainly mediated via the MDM2-p53 axis, which plays a prominent role in tumor suppression. Under normal conditions, low p53 expression is stringently regulated by its target gene, MDM2 E3 ligase, which induces p53 degradation in a ubiquitin-proteasome-dependent manner. Oncogenic signals induced by MYC, RAS, and E2Fs trap MDM2 in the inhibited state by inducing ARF expression as a safeguard measure, thereby activating the tumor-suppressive function of p53. In addition to the MDM2-p53 axis, ARF can also interact with diverse proteins and regulate various cellular functions, such as cellular senescence, apoptosis, and anoikis, in a p53-independent manner. As the evidence indicating ARF as a key tumor suppressor has been accumulated, there is growing evidence that ARF is sophisticatedly fine-tuned by the diverse factors through transcriptional and post-translational regulatory mechanisms. In this review, we mainly focused on how cancer cells employ transcriptional and post-translational regulatory mechanisms to manipulate ARF activities to circumvent the tumor-suppressive function of ARF. We further discussed the clinical implications of ARF in human cancer.

Download Full-text

miR-34a is not a candidate tumor suppressor

10.1101/2021.02.11.430795 ◽

2021 ◽

Author(s):

Sophie Mockly ◽

Élisabeth Houbron ◽

Hervé Seitz

Keyword(s):

Cell Proliferation ◽

Tumor Suppressor ◽

Cultured Cells ◽

Primary Tumors ◽

Suppressive Function ◽

Human Cancers ◽

Anti Cancer ◽

Tumorigenic Activity ◽

Tumor Suppressive Function ◽

Cancer Activity

The miR-34a microRNA (miRNA) is currently thought to act as a tumor suppressor: its locus is frequently deleted in human tumors and it is believed to repress cell proliferation. We re-visited the evidence of its anti-cancer activity. Our results show that miR-34a is not generally down-regulated in primary tumors relatively to normal adjacent tissues, and the occasional deletion of miR-34a in human cancers is not due to an anti-tumorigenic activity of that gene, but rather, to its genomic proximity with an actual tumor suppressor. Its anti-proliferative action was observed upon large, supra-physiological transfection of synthetic miR-34a in cultured cells, and our data indicates that endogenous miR-34a levels do not have such an effect. We thus conclude that the generally accepted tumor-suppressive function of miR-34a is erroneous.

Download Full-text

Prolyl hydroxylase 3 stabilizes the p53 tumor suppressor by inhibiting the p53–MDM2 interaction in a hydroxylase-independent manner

Journal of Biological Chemistry ◽

10.1074/jbc.ra118.007181 ◽

2019 ◽

Vol 294 (25) ◽

pp. 9949-9958 ◽

Cited By ~ 4

Author(s):

Yiming Xu ◽

Qiang Gao ◽

Yaqian Xue ◽

Xiuxiu Li ◽

Liang Xu ◽

...

Keyword(s):

Colon Cancer ◽

Tumor Suppressor ◽

P53 Protein ◽

Prolyl Hydroxylase ◽

Hydroxylase Activity ◽

Independent Manner ◽

P53 Expression ◽

Genetic Ablation ◽

Protein Levels

Prolyl hydroxylase 3 (PHD3) has initially been reported to hydroxylase hypoxia-inducible factor α (HIFα) and mediate HIFα degradation. More recent studies have shown that, in addition to HIFα, PHD3 has also other substrates. Moreover, pHD3 is believed to act as a tumor suppressor, but the underlying mechanism remains to be elucidated. Here, we demonstrate that PHD3 stabilizes p53 in a hydroxylase-independent manner. We found that PHD3 overexpression increases and PHD3 knockdown decreases p53 levels. Mechanistically, PHD3 bound MDM2 proto-oncogene (MDM2) and prevented MDM2 from interacting with p53, thereby inhibiting MDM2-mediated p53 degradation. Interestingly, we found that PHD3 overexpression could enhance p53 in the presence of the prolyl hydroxylase inhibitor dimethyloxalylglycine, and the prolyl hydroxylase activity-deficient variant PHD3-H196A also inhibited the p53-MDM2 interaction and stabilized p53. Genetic ablation of PHD3 decreased p53 protein levels in mice intestinal epithelial cells, but a genetic knockin of PHD3-H196A did not affect p53 protein levels in vivo. These results suggest that the prolyl hydroxylase activity of PHD3 is dispensable for its ability to stabilize p53. We found that both PHD3 and PHD3-H196A suppress the expression of the stem cell-associated gene NANOG and inhibited the properties of colon cancer stem cells through p53. Our results reveal an additional critical mechanism underlying the regulation of p53 expression and highlight that PHD3 plays a role in the suppression of colon cancer cell stemness in a hydroxylase-independent manner.

Download Full-text

AMBRA1 attenuates the proliferation of uveal melanoma cells

Open Medicine ◽

10.1515/med-2021-0386 ◽

2021 ◽

Vol 17 (1) ◽

pp. 1-14

Author(s):

Binbin Zhao ◽

Yun Yang ◽

Biyun Cun ◽

Ping Chen

Keyword(s):

Cell Division ◽

Cell Growth ◽

Tumor Suppressor ◽

Uveal Melanoma ◽

Human Cancer ◽

Therapeutic Targets ◽

E3 Ligase ◽

Beclin 1 ◽

Dependent Manner ◽

The Stability

Abstract Uveal melanoma (UVM) is the most common primary intraocular malignancy in adults with high metastasis rates. D-type cyclins (CCNDs) are central regulators of the cell division cycle and are among the most frequently deregulated therapeutic targets in human cancer. Recently, the E3 ligase adaptor, autophagy and beclin 1 regulator 1 (AMBRA1), was reported to regulate the stability of CCNDs, including CCND1, but its role in UVM has not been demonstrated. AMBRA1 is lowly expressed in UVM cells, and the ablation of AMBRA1 promotes the proliferation of 92.1 and OMM1 cells, whereas ectopically expressing AMBRA1 attenuates the proliferation of UVM cells. Further studies found that AMBRA1 promotes the ubiquitination and degradation of CCND1, and AMBRA1 regulates the proliferation of UVM cells in a CCND1-dependent manner. Thus, this study suggests that AMBRA1 serves as an important tumor suppressor by limiting UVM cell growth.

Download Full-text

Computational Identification of Tumor Suppressor Genes Based on Gene Expression Profiles in Normal and Cancerous Gastrointestinal Tissues

Journal of Oncology ◽

10.1155/2020/2503790 ◽

2020 ◽

Vol 2020 ◽

pp. 1-12

Author(s):

Qingrong Sun ◽

Md. Nazim Uddin ◽

Mengyuan Li ◽

Xiaosheng Wang ◽

Maode Lai

Keyword(s):

Gene Expression ◽

Small Intestine ◽

Tumor Suppressor ◽

Tumor Suppressor Genes ◽

Suppressor Genes ◽

Expression Levels ◽

Suppressive Function ◽

Normal Tissues ◽

Gi Cancers ◽

Tumor Suppressive Function

Cancer prevails in various gastrointestinal (GI) organs, such as esophagus, stomach, and colon. However, the small intestine has an extremely low cancer risk. It is interesting to investigate the molecular cues that could explain the significant difference in cancer incidence rates among different GI tissues. Using several large-scale normal and cancer tissue genomics datasets, we compared the gene expression profiling between small intestine and other GI tissues and between GI cancers and normal tissues. We identified 17 tumor suppressor genes (TSGs) which showed significantly higher expression levels in small intestine than in other GI tissues and significantly lower expression levels in GI cancers than in normal tissues. These TSGs were mainly involved in metabolism, immune, and cell growth signaling-associated pathways. Many TSGs had a positive expression correlation with survival prognosis in various cancers, confirming their tumor suppressive function. We demonstrated that the downregulation of many TSGs was associated with their hypermethylation in cancer. Moreover, we showed that the expression of many TSGs inversely correlated with tumor purity and positively correlated with antitumor immune response in various cancers, suggesting that these TSGs may exert their tumor suppressive function by promoting antitumor immunity. Furthermore, we identified a transcriptional regulatory network of the TSGs and their master transcriptional regulators (MTRs). Many of MTRs have been recognized as tumor suppressors, such as HNF4A, ZBTB7A, p53, and RUNX3. The TSGs could provide new molecular cues associated with tumorigenesis and tumor development and have potential clinical implications for cancer diagnosis, prognosis, and treatment.

Download Full-text

The p73 Tumor Suppressor Is Targeted by Pirh2 RING Finger E3 Ubiquitin Ligase for the Proteasome-dependent Degradation

Journal of Biological Chemistry ◽

10.1074/jbc.m111.261537 ◽

2011 ◽

Vol 286 (41) ◽

pp. 35388-35395 ◽

Cited By ~ 28

Author(s):

Yong-Sam Jung ◽

Yingjuan Qian ◽

Xinbin Chen

Keyword(s):

Tumor Suppressor ◽

Ubiquitin Ligase ◽

Human Cancer ◽

Ectopic Expression ◽

E3 Ubiquitin Ligase ◽

Ring Finger ◽

Growth Suppression ◽

Dependent Manner

The p73 gene, a homologue of the p53 tumor suppressor, is expressed as TA and ΔN isoforms. TAp73 has similar activity as p53 and functions as a tumor suppressor whereas ΔNp73 has both pro- and anti-survival functions. While p73 is rarely mutated in spontaneous tumors, the expression status of p73 is linked to the sensitivity of tumor cells to chemotherapy and prognosis for many types of human cancer. Thus, uncovering its regulators in tumors is of great interest. Here, we found that Pirh2, a RING finger E3 ubiquitin ligase, promotes the proteasome-dependent degradation of p73. Specifically, we showed that knockdown of Pirh2 up-regulates, whereas ectopic expression of Pirh2 down-regulates, expression of endogenous and exogenous p73. In addition, Pirh2 physically associates with and promotes TAp73 polyubiquitination both in vivo and in vitro. Moreover, we found that p73 can be degraded by both 20 S and 26 S proteasomes. Finally, we showed that Pirh2 knockdown leads to growth suppression in a TAp73-dependent manner. Taken together, our findings indicate that Pirh2 promotes the proteasomal turnover of TAp73, and thus targeting Pirh2 to restore TAp73-mediated growth suppression in p53-deficient tumors may be developed as a novel anti-cancer strategy.

Download Full-text

Targeting Post-Translational Regulation of p53 in Colorectal Cancer by Exploiting Vulnerabilities in the p53-MDM2 Axis

Cancers ◽

10.3390/cancers14010219 ◽

2022 ◽

Vol 14 (1) ◽

pp. 219

Author(s):

Chunwei W. Lai ◽

Cindy Xie ◽

Jean-Pierre Raufman ◽

Guofeng Xie

Keyword(s):

Colorectal Cancer ◽

Translational Regulation ◽

Nuclear Translocation ◽

Suppressor Gene ◽

Regulatory Mechanisms ◽

Missense Mutations ◽

P53 Expression ◽

Ubiquitin Protein Ligase ◽

The Past ◽

Tumor Survival

The role played by the key tumor suppressor gene p53 and the implications of p53 mutations for the development and progression of neoplasia continue to expand. This review focuses on colorectal cancer and the regulators of p53 expression and activity identified over the past decade. These newly recognized regulatory mechanisms include (1) direct regulation of mouse double minute 2 homolog (MDM2), an E3 ubiquitin-protein ligase; (2) modulation of the MDM2-p53 interaction; (3) MDM2-independent p53 degradation; and (4) inhibition of p53 nuclear translocation. We positioned these regulatory mechanisms in the context of p53 missense mutations, which not only evade canonical p53 degradation machinery but also exhibit gain-of-function phenotypes that enhance tumor survival and metastasis. Lastly, we discuss current and potential therapeutic strategies directed against p53 mutant-bearing tumors.

Download Full-text

ARID1 proteins: from transcriptional and post-translational regulation to carcinogenesis and potential therapeutics

Epigenomics ◽

10.2217/epi-2020-0414 ◽

2021 ◽

Author(s):

Olena Odnokoz ◽

Cindy Wavelet-Vermuse ◽

Shelby L Hophan ◽

Serdar Bulun ◽

Yong Wan

Keyword(s):

Chromatin Remodeling ◽

Translational Regulation ◽

Current Knowledge ◽

Human Cancer ◽

Regulatory Mechanisms ◽

Cell Functions ◽

Human Cancers ◽

Low Levels ◽

Potential Therapeutics

The ARID1 proteins are mutually exclusive subunits of the BRG1/BRM-associated factor (BAF) complexes that play an important role in chromatin remodeling and regulate many fundamental cell functions. The role of ARID1s is well defined as a tumor-suppressive. The cancer cells evolve different mechanisms to downregulate ARID1s and inactivate their functions. ARID1s are frequently mutated in human cancer. The recent findings of ARID1A/B downregulation at transcriptional and translational levels along with their low levels in human cancers indicate the significance of regulatory mechanisms of ARID1s in cancers. In this review, we present the current knowledge on the regulation and alterations of ARID1 protein expression in human cancers and indicate the importance of regulators of ARID1s as a prognostic marker and in potential therapeutic strategies.

Download Full-text

Hsp90 chaperone code and the tumor suppressor VHL cooperatively regulate the mitotic checkpoint

Cell Stress and Chaperones ◽

10.1007/s12192-021-01240-2 ◽

2021 ◽

Author(s):

Mark R. Woodford ◽

Sarah J. Backe ◽

Laura A. Wengert ◽

Diana M. Dunn ◽

Dimitra Bourboulia ◽

...

Keyword(s):

Tumor Suppressor ◽

Translational Regulation ◽

Heat Shock Protein 90 ◽

Mitotic Checkpoint ◽

Vital Role ◽

Independent Manner ◽

Von Hippel Lindau ◽

Chaperone Function ◽

Hsp90 Chaperone ◽

The Stability

AbstractHeat shock protein-90 (Hsp90) is an essential molecular chaperone in eukaryotes that plays a vital role in protecting and maintaining the functional integrity of deregulated signaling proteins in tumors. We have previously reported that the stability and activity of the mitotic checkpoint kinase Mps1 depend on Hsp90. In turn, Mps1-mediated phosphorylation Hsp90 regulates its chaperone function and is essential for the mitotic arrest. Cdc14-assisted dephosphorylation of Hsp90 is vital for the mitotic exit. Post-translational regulation of Hsp90 function is also known as the Hsp90 “Chaperone Code.” Here, we demonstrate that only the active Mps1 is ubiquitinated on K86, K827, and K848 by the tumor suppressor von Hippel-Lindau (VHL) containing E3 enzyme, in a prolyl hydroxylation-independent manner and degraded in the proteasome. Furthermore, we show that this process regulates cell exit from the mitotic checkpoint. Collectively, our data demonstrates an interplay between the Hsp90 chaperone and VHL degradation machinery in regulating mitosis.

Download Full-text

Platelet-Rich and Platelet-Poor Plasma Might Play Supportive Roles in Cancer Cell Culture: A Replacement for Fetal Bovine Serum?

Anti-Cancer Agents in Medicinal Chemistry ◽

10.2174/1871520621999210101225912 ◽

2021 ◽

Vol 21 ◽

Author(s):

Mehdi Talebi ◽

Mousa Vatanmakanian ◽

Ali Mirzaei ◽

Yaghoub Barfar ◽

Maryam Hemmatzadeh ◽

...

Keyword(s):

Cell Culture ◽

Cell Growth ◽

Cancer Cell ◽

Human Cancer ◽

High Price ◽

Dependent Manner ◽

Platelet Poor Plasma ◽

Protein Levels ◽

Healthy Donors ◽

Regulatory Functions

Background: Platelet-rich (PRP) and Platelet-poor plasma (PPP) are widely used in research and clinical platforms mainly due to their capacities to enhance cell growth. Although short half-life (5 days) and the high price of platelet products pose challenges regarding their usage, they maintain the growth regulatory functions for weeks. Thus, we aimed to assess the supplementary values of these products in human CCRF-CEM cancer cells. Mechanistically, we also checked if the PRP/PPP treatment enhances YKL-40 expression as a known protein regulating cell growth. Methods: The PRP/PPP was prepared from healthy donors using manual stepwise centrifugation and phase separation. The viability of the cells treated with gradient PRP/PPP concentrations (2, 5, 10, and 15%) was measured by the MTT assay. The YKL-40 mRNA and protein levels were assessed using qRT-PCR and western blotting. The data were compared to FBS-treated cells. Result: Our findings revealed that the cells treated by PRP/PPP not only were morphologically comparable to those treated by FBS but also, they showed greater viability at the concentrations of 10 and 15%. Moreover, it was shown that PRP/PPP induce cell culture support, at least in part, via inducing YKL-40 expression at both mRNA and protein levels in a time- and dose-dependent manner. Conclusion: Collectively, by showing cell culture support comparable to FBS, the PRP/PPP might be used as good candidates to supplement the cancer cell culture and overcome concerns regarding the use of FBS as a non-human source in human cancer research.

Download Full-text

Arginine Methyltransferase PRMT1 Regulates p53 Activity in Breast Cancer

Life ◽

10.3390/life11080789 ◽

2021 ◽

Vol 11 (8) ◽

pp. 789

Author(s):

Li-Ming Liu ◽

Qiang Tang ◽

Xin Hu ◽

Jing-Jing Zhao ◽

Yuan Zhang ◽

...

Keyword(s):

Breast Cancer ◽

Cell Growth ◽

Cancer Cells ◽

Breast Cancer Cells ◽

Asymmetric Dimethylarginine ◽

Human Cancer ◽

Specific Inhibitor ◽

Dependent Manner ◽

Breast Tumorigenesis ◽

Stress Signals

The protein p53 is one of the most important tumor suppressors, responding to a variety of stress signals. Mutations in p53 occur in about half of human cancer cases, and dysregulation of the p53 function by epigenetic modifiers and modifications is prevalent in a large proportion of the remainder. PRMT1 is the main enzyme responsible for the generation of asymmetric-dimethylarginine, whose upregulation or aberrant splicing has been observed in many types of malignancies. Here, we demonstrate that p53 function is regulated by PRMT1 in breast cancer cells. PRMT1 knockdown activated the p53 signal pathway and induced cell growth-arrest and senescence. PRMT1 could directly bind to p53 and inhibit the transcriptional activity of p53 in an enzymatically dependent manner, resulting in a decrease in the expression levels of several key downstream targets of the p53 pathway. We were able to detect p53 asymmetric-dimethylarginine signals in breast cancer cells and breast cancer tissues from patients, and the signals could be significantly weakened by silencing of PRMT1 with shRNA, or inhibiting PRMT1 activity with a specific inhibitor. Furthermore, PRMT1 inhibitors significantly impeded cell growth and promoted cellular senescence in breast cancer cells and primary tumor cells. These results indicate an important role of PRMT1 in the regulation of p53 function in breast tumorigenesis.

Download Full-text