Mutant p53 antagonizes p63/p73-mediated tumor suppression via Notch1

TP53 mutations in cancer: Molecular features and therapeutic opportunities (Review)

The tumour suppressor factor p53 plays an essential role in regulating numerous cellular processes, including the cell cycle, DNA repair, apoptosis, autophagy, cell metabolism and immune response. TP53 is the most commonly mutated gene in human cancers. These mutations are primarily non‑synonymous changes that produce mutant p53 proteins characterized by loss of function, a dominant negative effect on p53 tetramerisation and gain of function (GOF). GOF mutations not only disrupt the tumour‑suppressive activities of p53 but also endow the mutant proteins with new oncogenic properties. Recent studies analysing different pathogenic features of mutant p53 in cancer‑derived cell lines have demonstrated that restoring wild‑type p53, rather than removing GOF mutations, reduces cancer cell growth. These findings suggest that therapeutic strategies for reactivating wild‑type p53 function in cancer cells may bring a greater benefit than approaches halting mutant p53. This approach could involve the use of small molecules, gene therapy and other methods to re‑establish wild‑type p53 activity. This review describes the complexity of the biological activities of different p53 mutants and summarizes the current therapeutic approaches to restore p53 function.

Impact of p53-associated acute myeloid leukemia hallmarks on metabolism and the immune environment

Acute myeloid leukemia (AML), an aggressive malignancy of hematopoietic stem cells, is characterized by the blockade of cell differentiation, uncontrolled proliferation, and cell expansion that impairs healthy hematopoiesis and results in pancytopenia and susceptibility to infections. Several genetic and chromosomal aberrations play a role in AML and influence patient outcomes. TP53 is a key tumor suppressor gene involved in a variety of cell features, such as cell-cycle regulation, genome stability, proliferation, differentiation, stem-cell homeostasis, apoptosis, metabolism, senescence, and the repair of DNA damage in response to cellular stress. In AML, TP53 alterations occur in 5%-12% of de novo AML cases. These mutations form an important molecular subgroup, and patients with these mutations have the worst prognosis and shortest overall survival among patients with AML, even when treated with aggressive chemotherapy and allogeneic stem cell transplant. The frequency of TP53-mutations increases in relapsed and recurrent AML and is associated with chemoresistance. Progress in AML genetics and biology has brought the novel therapies, however, the clinical benefit of these agents for patients whose disease is driven by TP53 mutations remains largely unexplored. This review focuses on the molecular characteristics of TP53-mutated disease; the impact of TP53 on selected hallmarks of leukemia, particularly metabolic rewiring and immune evasion, the clinical importance of TP53 mutations; and the current progress in the development of preclinical and clinical therapeutic strategies to treat TP53-mutated disease.

Unraveling the dual role of ADAM10: Bridging the gap between cancer and Alzheimer's disease

An inverse association between Alzheimer's disease (AD) and cancer has been proposed. Patients with a cancer history have a decreased risk of developing AD, and AD patients have a reduced cancer incidence, which is not seen in vascular dementia patients. Given this association, common molecular and biological mechanisms that could explain this inverse relationship have been proposed before, such as Peptidylprolyl Cis/Trans Isomerase, NIMA-Interacting 1 (Pin1), Wingless and Int-1 (Wnt), and transformation-related protein 53 (p53)-mediated pathways, along with inflammation and oxidative stress-related proteins. A Disintegrin And Metalloprotease 10 (ADAM10) is a protease responsible for the cleavage of key AD- and cancer-related substrates, and it has inverse roles in those diseases: neuroprotective and disease-promoting, respectively. Thus, herein, we review the relevant literature linking AD and cancer and propose how ADAM10 activity might modulate the inverse association between the diseases. Understanding how this protease mediates those two conditions might raise some considerations in the ADAM10 pharmacological modulation for treating AD and cancer.

Extracellular matrix protein 1 (ECM1) is a potential biomarker in B cell acute lymphoblastic leukemia

B cell acute lymphoblastic leukemia (ALL) is characterized by the highly heterogeneity of pathogenic genetic background, and there are still approximately 30-40% of patients without clear molecular markers. To identify the dysregulated genes in B cell ALL, we screened 30 newly diagnosed B cell ALL patients and 10 donors by gene expression profiling chip. We found that ECM1 transcription level was abnormally elevated in newly diagnosed B cell ALL and further verified in another 267 cases compared with donors (median, 124.57% vs. 7.14%, P < 0.001). ROC analysis showed that the area under the curve of ECM1 transcription level at diagnosis was 0.89 (P < 0.001). Patients with BCR::ABL1 and IKZF1 deletion show highest transcription level (210.78%) compared with KMT2A rearrangement (39.48%) and TCF3::PBX1 rearrangement ones (30.02%) (all P < 0.05). Also, the transcription level of ECM1 was highly correlated with the clinical course, as 20 consecutive follow-up cases indicated. The 5-year OS of patients (non-KMT2A and non-TCF3::PBX1 rearrangement) with high ECM1 transcription level was significantly worse than the lower ones (18.7% vs. 72.9%, P < 0.001) and high ECM1 transcription level was an independent risk factor for OS (HR = 5.77 [1.75-19.06], P = 0.004). After considering transplantation, high ECM1 transcription level was not an independent risk factor, although OS was still poor (low vs. high, 71.1% vs. 56.8%, P = 0.038). Our findings suggested that ECM1 may be a potential molecular marker for diagnosis, minimal residual disease (MRD) monitoring, and prognosis prediction of B cell ALL.Trial registration Trial Registration Registered in the Beijing Municipal Health Bureau Registration N 2007-1007 and in the Chinese Clinical Trial Registry [ChiCTR-OCH-10000940 and ChiCTR-OPC-14005546]; http://www.chictr.org.cn .

p63: a crucial player in epithelial stemness regulation

Epithelial tissue homeostasis is closely associated with the self-renewal and differentiation behaviors of epithelial stem cells (ESCs). p63, a well-known marker of ESCs, is an indispensable factor for their biological activities during epithelial development. The diversity of p63 isoforms expressed in distinct tissues allows this transcription factor to have a wide array of effects. p63 coordinates the transcription of genes involved in cell survival, stem cell self-renewal, migration, differentiation, and epithelial-to-mesenchymal transition. Through the regulation of these biological processes, p63 contributes to, not only normal epithelial development, but also epithelium-derived cancer pathogenesis. In this review, we provide an overview of the role of p63 in epithelial stemness regulation, including self-renewal, differentiation, proliferation, and senescence. We describe the differential expression of TAp63 and ΔNp63 isoforms and their distinct functional activities in normal epithelial tissues and in epithelium-derived tumors. Furthermore, we summarize the signaling cascades modulating the TAp63 and ΔNp63 isoforms as well as their downstream pathways in stemness regulation.

Isoform-specific disruption of the TP73 gene reveals a critical role for TAp73γ in tumorigenesis via leptin

TP73, a member of the p53 family, is expressed as TAp73 and ΔNp73 along with multiple C-terminal isoforms (α-η). ΔNp73 is primarily expressed in neuronal cells and necessary for neuronal development. Interestingly, while TAp73α is a tumor suppressor and predominantly expressed in normal cells, TAp73 is found to be frequently altered in human cancers, suggesting a role of TAp73 C-terminal isoforms in tumorigenesis. To test this, the TCGA SpliceSeq database was searched and showed that exon 11 (E11) exclusion occurs frequently in several human cancers. We also found that p73α to p73γ isoform switch resulting from E11 skipping occurs frequently in human prostate cancers and dog lymphomas. To determine whether p73α to p73γ isoform switch plays a role in tumorigenesis, CRISPR technology was used to generate multiple cancer cell lines and a mouse model in that Trp73 E11 is deleted. Surprisingly, we found that in E11-deificient cells, p73γ becomes the predominant isoform and exerts oncogenic activities by promoting cell proliferation and migration. In line with this, E11-deficient mice were more prone to obesity and B-cell lymphomas, indicating a unique role of p73γ in lipid metabolism and tumorigenesis. Additionally, we found that E11-deficient mice phenocopies Trp73-deficient mice with short lifespan, infertility, and chronic inflammation. Mechanistically, we showed that Leptin, a pleiotropic adipocytokine involved in energy metabolism and oncogenesis, was highly induced by p73γ,necessary for p73γ-mediated oncogenic activity, and associated with p73α to γ isoform switch in human prostate cancer and dog lymphoma. Finally, we showed that E11-knockout promoted, whereas knockdown of p73γ or Leptin suppressed, xenograft growth in mice. Our study indicates that the p73γ-Leptin pathway promotes tumorigenesis and alters lipid metabolism, which may be targeted for cancer management.

TP73 Isoform-specific disruption reveals a critical role of TAp73beta in growth suppression and inflammatory response

TP73 is expressed as multiple N- and C-terminal isoforms through two separate promoters or alternative splicing. While N-terminal p73 isoforms have been well studied, very little is known about p73 C-terminal isoforms. Thus, CRISPR was used to delete TP73 Exon13 (E13-KO) to induce p73α to p73β isoform switch. We showed that E13-KO led to decreased cell proliferation and migration and sensitized cells to ferroptosis, which can be reverted by knockdown of TAp73β in E13-KO cells. To understand the biological function of p73β in vivo, we generated a mouse model in that the Trp73 E13 was deleted by CRISPR. We showed that p73α to p73β isoform switch led to increased cellular senescence in mouse embryonic fibroblasts. We also showed that E13-deficient mice exhibited shorter life span and were prone to spontaneous tumors, chronic inflammation and liver steatosis as compared to WT mice. Additionally, we found that the incidence of chronic inflammation and liver steatosis was higher in E13-deficient mice than that in Trp73-deficient mice, suggesting that p73β is a strong inducer of inflammatory response. Mechanistically, we showed that TAp73β was able to induce cysteine dioxygenase 1 (CDO-1), leading to cysteine depletion and subsequently, enhanced ferroptosis and growth suppression. Conversely, knockdown of CDO-1 was able to alleviate the growth suppression and ferroptosis in E13-KO cells. Together, our data suggest that at a physiologically relevant level, TAp73β is a strong inducer of growth suppression but insufficient to compensate for loss of TAp73α in tumor suppression due to aberrant induction of inflammatory response and liver steatosis.

Reactivation of mutant p53 in esophageal squamous cell carcinoma by isothiocyanate inhibits tumor growth

p53 mutations are prevalent in human cancers; approximately half of patients with esophageal cancer present these mutations. Mutant p53 (mutp53) exerts oncogenic functions that promote malignant tumor progression, invasion, metastasis, and drug resistance, resulting in poor prognosis. Some small molecules have been shown to mitigate the oncogenic function of mutp53 by restoring its wild-type activity. Although these molecules have been evaluated in clinical trials, none have been successfully used in the clinic. Here, we investigated the antitumor effects of phenethyl isothiocyanate (PEITC) in p53-mutant esophageal squamous cell carcinoma (ESCC) and elucidated its mechanism to identify new therapeutic strategies. We observed that p53^R248Q is a DNA contact mutation and a structural mutation and that PEITC can restore the activity of p53^R248Q in vitro and in vivo, further clarifying the antitumor activity of PEITC in cancers with different types of p53 mutations. PEITC can inhibit ESCC growth, induce apoptosis, and arrest cell cycle progression and has a preferential selectivity for ESCC with p53 mutations. Mechanistic studies showed that PEITC induced apoptosis and arrested cells at G2/M transition in cells expressing the p53^R248Q mutant by restoring the wild-type conformation and transactivation function of p53; these effects were concentration dependent. Furthermore, PEITC inhibited the growth of subcutaneous xenografts in vivo and restored p53 mutant activity in xenografts. According to these findings, PEITC has antitumor effects, with its ability to restore p53^R248Q activity being a key molecular event responsible for these effects.

p73 isoforms meet evolution of metastasis

Cancer largely adheres to Darwinian selection. Evolutionary forces are prominent during metastasis, the final and incurable disease stage, where cells acquire combinations of advantageous phenotypic features and interact with a dynamically changing microenvironment, in order to overcome the metastatic bottlenecks, while therapy exerts additional selective pressures. As a strategy to increase their fitness, tumors often co-opt developmental and tissue-homeostasis programs. Herein, 25 years after its discovery, we review TP73, a sibling of the cardinal tumor-suppressor TP53, through the lens of cancer evolution. The TP73 gene regulates a wide range of processes in embryonic development, tissue homeostasis and cancer via an overwhelming number of functionally divergent isoforms. We suggest that TP73 neither merely mimics TP53 via its p53-like tumor-suppressive functions, nor has black-or-white-type effects, as inferred by the antagonism between several of its isoforms in processes like apoptosis and DNA damage response. Rather, under dynamic conditions of selective pressure, the various p73 isoforms which are often co-expressed within the same cancer cells may work towards a common goal by simultaneously activating isoform-specific transcriptional and non-transcriptional programs. Combinatorial co-option of these programs offers selective advantages that overall increase the likelihood for successfully surpassing the barriers of the metastatic cascade. The p73 functional pleiotropy-based capabilities might be present in subclonal populations and expressed dynamically under changing microenvironmental conditions, thereby supporting clonal expansion and propelling evolution of metastasis. Deciphering the critical p73 isoform patterns along the spatiotemporal axes of tumor evolution could identify strategies to target TP73 for prevention and therapy of cancer metastasis.

Mutant p53 in cancer: from molecular mechanism to therapeutic modulation

TP53, a crucial tumor suppressor gene, is the most commonly mutated gene in human cancers. Aside from losing its tumor suppressor function, mutant p53 (mutp53) often acquires inherent, novel oncogenic functions, which is termed "gain-of-function". Emerging evidence suggests that mutp53 is highly associated with advanced malignancies and poor prognosis, which makes it a target for development of novel cancer therapies. Herein, we provide a summary of our knowledge of the mutp53 types and mutp53 spectrum in cancers. The mechanisms of mutp53 accumulation and gain-of-function are also summarized. Furthermore, we discuss the gain-of-function of mutp53 in cancers: genetic instability, ferroptosis, microenvironment, and stemness. Importantly, the role of mutp53 in the clinic is also discussed, particularly with regard to chemotherapy and radiotherapy. Last, emphasis is given to emerging strategies on how to target mutp53 for tumor therapy. Thus, this review will contribute to better understanding of the significance of mutp53 as a target for therapeutic strategies.

Inactivation of tumor suppressor TAp63 by hepatitis B virus X protein in hepatocellular carcinoma

BACKGROUND

The hepatitis B virus X (HBx) protein plays a critical role in the initiation and progression of hepatitis B virus (HBV)-associated hepatocellular carcinoma (HCC). In the early stage of the disease, HBx facilitates tumor onset by inactivating the tumor suppressor p53. The p53-encoding gene, however, is frequently mutated or deleted as the cancer progresses to the late stage and, under such circumstance, the p53 homolog TAp63 can harness HCC growth by transactivating several important p53-target genes.

METHODS

To determine whether HBx regulates TAp63, we performed co-immunoprecipitation assay, real-time quantitative polymerase chain reaction, immunoblotting, and flow cytometry analysis in p53-null cancer cell lines, Hep3B and H1299.

RESULTS

HBx interacts with the transactivation domain of TAp63, as HBx was co-immunoprecipitated with TAp63 but not with ΔNp63. The interaction between HBx and TAp63 abolished transcriptional activity of TAp63, as evidenced by the reduction of the levels of its target genes p21 and PUMA , consequently leading to restricted apoptosis and augmented proliferation of HCC cells.

CONCLUSION

HBV induces progression of HCC that harbors defective p53 by inhibiting the tumor suppressor TAp63.

p73α1, a p73 C-terminal isoform, regulates tumor suppression and the inflammatory response via Notch1

Significance p73 is expressed as multiple C-terminal isoforms, but their expression and activity are largely unknown. Here, we identified p73α1 as a p73 C-terminal isoform that results from exon 12 (E12) exclusion. We showed that E12 deficiency in mice leads to systemic inflammation but not spontaneous tumors. We also showed that Notch1 is regulated by p73α1 and plays a critical role in p73-dependent tumor suppression and systemic inflammation.

TP53 mutations upregulate RCP expression via Sp1/3 to drive lung cancer progression

Mutant p53 (mtp53) can exert cancer-promoting activities via "gain-of-function", which has become a popular research target. Although lots of researchers focus on the tumor-suppressor role for p53, the regulation of mutant p53 remains unknown. Here, we report a mechanism by which mtp53 regulate the transcription of Rab coupling protein (RCP) to influence lung cancer behavior. First, we show that RCP is specifically expressed at high levels in lung cancer tissues and cells, and RCP knockout suppresses tumor growth and metastasis. Further mass spectrometry and functional analysis identify that Sp1, Sp3 and Stat3 are the transcriptional activators of RCP. Moreover, p53 is involved in modulating RCP expression in an Sp1/3 dependent manner. Mechanistically, in contrast to wild-type p53 suppression of RCP transcription by decreasing Sp1/3 proteins, TP53 mutations have changed on Sp1/3 expression via "loss-of-function". Surprisingly, the DNA contact mutants of p53 further robustly enhance their binding ability with Sp1/3 to drive RCP expression through the "gain-of-function" activity. Collectively, we reveal a mechanism by which p53 regulating the transcription of RCP to influence lung cancer progression, which provides new insights for treating p53 mutant lung cancer.

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

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.

Induction of Apoptosis and Autophagy by Ternary Copper Complex Towards Breast Cancer Cells

BACKGROUND

Copper complex has been gaining much attention in anticancer research as targeted agent since cancer cells uptake more copper than non-cancerous cells. Our group has synthesised a ternary copper complex which is composed of 1,10-phenanthroline and tyrosine [Cu(phen)(L-tyr)Cl].3H₂0. These two payloads are designed to cleave DNA and inhibit protein degradation system (proteasome) concurrently in cancer cells, making this copper complex a dual-target compound.

OBJECTIVE

Current study was carried out to investigate the mode of cell death and role of autophagy induced by [Cu(phen)(L-tyr)Cl].3H₂0 in MCF-7 and MDA-MB-231 breast cancer cells.

METHODS

Growth inhibition of [Cu(phen)(L-tyr)Cl].3H₂0 towards MDA-MB-231 and human non-cancerous MCF10A breast cells was determined by MTT assay. Annexin-V-FITC/PI and cell cycle analysis were evaluated by flow cytometry. The expression of p53, Bax, caspase-9, caspase-7, caspase-3 and LC3 were determined using western blot analysis. The cells were then co-treated with hydroxychloroquine to ascertain the role of autophagy induced by [Cu(phen)(L-tyr)Cl].3H₂0.

RESULTS

[Cu(phen)(L-tyr)Cl].3H20 inhibited the growth of cancer cells dose-dependently with less toxicity towards MCF10A cells. Additionally, [Cu(phen)(L-tyr)Cl].3H20 induced apoptosis and cell cycle arrest towards MCF-7 and MDA-MB-231 breast cancer cells possibly via regulation of p53, Bax, caspase-9, caspase-3 and capase-7. The expression of LC3II was upregulated in both cancer cell lines upon treatment with [Cu(phen)(L-tyr) Cl].3H₂0, indicating the induction of autophagy. Co-treatment with autophagy inhibitor hydroxychloroquine significantly enhanced growth inhibition of both cell lines, suggesting that the autophagy induced by [Cu(phen)(L-tyr) Cl].3H₂0 in both breast cancer cells was promoting cell survival.

CONCLUSION

[Cu(phen)(L-tyr)Cl].3H20 holds great potential to be developed for breast cancer treatment.

Small Proline-Rich Protein 2A and 2D Are Regulated by the RBM38-p73 Axis and Associated with p73-Dependent Suppression of Chronic Inflammation

Simple Summary

Small proline-rich protein 2A and 2D (SPRR2A and SPRR2D) are structure proteins of cornified cell envelopes and function as a protective barrier against diverse external insults. However, the role of SPRR2A/2D in chronic inflammation remains unclear. Here, we showed that SPRR2A/2D expression is controlled by a regulatory loop formed by RNA-binding protein RBM38 and tumor suppressor p73. We also found that RBM38-mediated expression of SPRR2A/2D was p73-dependent and that induction of SPRR2A/2D during keratinocyte differentiation was dependent on both p73 and Rbm38. Furthermore, We found that Rbm38^−/−;Trp73^+/− mice exhibited weak expression of SPRR2A/2D in multiple tissues and were susceptible to systemic chronic inflammation. Together, our data reveal that SPRR2A/2D are novel targets of the RBM38-p73 loop and contribute to p73-dependent suppression of chronic inflammation.

Abstract

Small proline-rich protein 2A and 2D (SPRR2A and SPRR2D) provide barrier function in terminally differentiated stratified squamous epithelia through the epidermal differentiation complex. However, little is known how SPRR2A/2D expression is controlled and their role in chronic inflammation. Here, we showed that that SPRR2A/2D expression is controlled by a regulatory loop formed by RNA-binding protein RBM38 and tumor suppressor p73. Specifically, we found that SPRR2A/2D expression was induced by ectopic expression of RBM38 or p73 but suppressed by knockout of Rbm38 or p73. We also found that RBM38-mediated expression of SPRR2A/2D was p73-dependent and that induction of SPRR2A/2D during keratinocyte differentiation was dependent on both p73 and Rbm38. Additionally, we found that SPRR2A/2D expression was closely associated with p73 expression in normal and cancerous tissues. To determine the biological function of the RBM38-p73 loop potentially via SPRR2A/2D, we generated a cohort of wild-type, Rbm38^−/−, Trp73^+/−, and Rbm38^−/−;Trp73^+/− mice. We found that Rbm38^−/−;Trp73^+/− mice had a much shorter lifespan than that for Rbm38^−/−—and to a lesser extent for Trp73^+/− mice—but were less prone to spontaneous tumors than Trp73^+/− or Rbm38^−/− mice. We also found that Rbm38^−/−;Trp73^+/− mice exhibited weak expression of SPRR2A/2D in multiple tissues and were susceptible to systemic chronic inflammation, suggesting that decreased SPRR2A/2D expression is likely responsible for chronic inflammation in Rbm38^−/−;Trp73^+/− mice, leading to a shortened lifespan. Together, our data reveal that SPRR2A/2D are novel targets of the RBM38-p73 loop and contribute to p73-dependent suppression of chronic inflammation.

Porcine model elucidates function of p53 isoform in carcinogenesis and reveals novel circTP53 RNA

Recent years have seen an increasing number of genetically engineered pig models of human diseases including cancer. We previously generated pigs with a modified TP53 allele that carries a Cre-removable transcriptional stop signal in intron 1, and an oncogenic mutation TP53R167H (orthologous to human TP53R175H) in exon 5. Pigs with the unrecombined mutant allele (flTP53R167H) develop mainly osteosarcoma but also nephroblastomas and lymphomas. This observation suggested that TP53 gene dysfunction is itself the key initiator of bone tumorigenesis, but raises the question which aspects of the TP53 regulation lead to the development of such a narrow tumour spectrum. Molecular analysis of p53 revealed the presence of two internal TP53 promoters (Pint and P2) equivalent to those found in human. Consequently, both pig and human express TP53 isoforms. Data presented here strongly suggest that P2-driven expression of the mutant R167H-Δ152p53 isoform (equivalent to the human R175H-Δ160p53 isoform) and its circular counterpart circTP53 determine the tumour spectrum and play a critical role in the malignant transformation in flTP53R167H pigs. The detection of Δ152p53 isoform mRNA in serum is indicative of tumorigenesis. Furthermore, we showed a tissue-specific p53-dependent deregulation of the p63 and p73 isoforms in these tumours. This study highlights important species-specific differences in the transcriptional regulation of TP53. Considering the similarities of TP53 regulation between pig and human, these observations provide useful pointers for further investigation into isoform function including the novel circTP53 in both the pig model and human patients.

TAp73β Can Promote Hepatocellular Carcinoma Dedifferentiation

Simple Summary

Hepatocellular carcinoma (HCC) is a highly complex and heterogeneous type of cancer. Hepatocyte dedifferentiation is one of the important steps in the development of HCC. However, its molecular mechanisms are not well known. In this study, we report that transcriptionally active TAp73 isoforms are overexpressed in HCC. We also show that TAp73β suppresses the expression of the hepatocyte markers including CYP3A4, AFP, ALB, HNF4α, while increasing the expression of several cholangiocyte markers in HCC cell lines. In conclusion, this report reveals a pro-oncogenic role for TAp73β in liver cancer.

Abstract

Hepatocyte dedifferentiation is a major source of hepatocellular carcinoma (HCC), but its mechanisms are unknown. We explored the p73 expression in HCC tumors and studied the effects of transcriptionally active p73β (TAp73β) in HCC cells. Expression profiles of p73 and patient clinical data were collected from the Genomic Data Commons (GDC) data portal and the TSVdb database, respectively. Global gene expression profiles were determined by pan-genomic 54K microarrays. The Gene Set Enrichment Analysis method was used to identify TAp73β-regulated gene sets. The effects of TAp73 isoforms were analyzed in monolayer cell culture, 3D-cell culture and xenograft models in zebrafish using western blot, flow cytometry, fluorescence imaging, real-time polymerase chain reaction (RT-PCR), immunohistochemistry and morphological examination. TAp73 isoforms were significantly upregulated in HCC, and high p73 expression correlated with poor patient survival. The induced expression of TAp73β caused landscape expression changes in genes involved in growth signaling, cell cycle, stress response, immunity, metabolism and development. Hep3B cells overexpressing TAp73β had lost hepatocyte lineage biomarkers including ALB, CYP3A4, AFP, HNF4α. In contrast, TAp73β upregulated genes promoting cholangiocyte lineage such as YAP, JAG1 and ZO-1, accompanied with an increase in metastatic ability. Our findings suggest that TAp73β may promote malignant dedifferentiation of HCC cells.

FDXR regulates TP73 tumor suppressor via IRP2 to modulate aging and tumor suppression

Ferredoxin reductase (FDXR) is a mitochondrial flavoprotein that initiates electron transport from NADPH to several cytochromes P450 via two electron carriers, ferredoxin 1 (FDX1) and FDX2. FDXR is the sole ferredoxin reductase in humans and plays a critical role in steroidogenesis and biosynthesis of heme and iron-sulfur clusters. However, much less is known about the role of FDXR in cancer. Here, we show that FDXR plays a role in tumorigenesis by modulating expression of the tumor suppressor p73. By using genetically modified mouse models, we recently showed that mice deficient in either Fdxr or Trp73 had a shorter lifespan and were prone to spontaneous tumors as compared with wild-type (WT) mice. Interestingly, compound Trp73 ^+/- ;Fdxr ^+/- mice lived longer and developed fewer tumors when compared with Fdxr ^+/- or Trp73 ^+/- mice. Moreover, we found that cellular senescence was increased in Trp73 ^+/- and Fdxr ^+/- mouse embryonic fibroblasts (MEFs), which was further increased in Trp73 ^+/- ;Fdxr ^+/- MEFs, as compared with that in WT MEFs. As FDXR is regulated by p73, we examined whether there was a feedback regulation between p73 and FDXR. Indeed, we found that Trp73 expression was decreased by loss of Fdxr in MEFs and that FDXR is required for p73 expression in multiple human cancer cell lines independent of p53. Mechanistically, we found that loss of FDXR, via FDX2, increased expression of iron-binding protein 2 (IRP2), which subsequently repressed TP73 mRNA stability. We also showed that TP73 transcript contained an iron response element in its 3'UTR, which was required for IRP2 to destabilize TP73 mRNA. Together, these data reveal a novel regulation of p73 by FDXR via IRP2 and that the FDXR-p73 axis plays a critical role in aging and tumor suppression. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Mutant p53 Gain-of-Function: Role in Cancer Development, Progression, and Therapeutic Approaches

Frequent p53 mutations (mutp53) not only abolish tumor suppressor capacities but confer various gain-of-function (GOF) activities that impacts molecules and pathways now regarded as central for tumor development and progression. Although the complete impact of GOF is still far from being fully understood, the effects on proliferation, migration, metabolic reprogramming, and immune evasion, among others, certainly constitute major driving forces for human tumors harboring them. In this review we discuss major molecular mechanisms driven by mutp53 GOF. We present novel mechanistic insights on their effects over key functional molecules and processes involved in cancer. We analyze new mechanistic insights impacting processes such as immune system evasion, metabolic reprogramming, and stemness. In particular, the increased lipogenic activity through the mevalonate pathway (MVA) and the alteration of metabolic homeostasis due to interactions between mutp53 and AMP-activated protein kinase (AMPK) and Sterol regulatory element-binding protein 1 (SREBP1) that impact anabolic pathways and favor metabolic reprograming. We address, in detail, the impact of mutp53 over metabolic reprogramming and the Warburg effect observed in cancer cells as a consequence, not only of loss-of-function of p53, but rather as an effect of GOF that is crucial for the imbalance between glycolysis and oxidative phosphorylation. Additionally, transcriptional activation of new targets, resulting from interaction of mutp53 with NF-kB, HIF-1α, or SREBP1, are presented and discussed. Finally, we discuss perspectives for targeting molecules and pathways involved in chemo-resistance of tumor cells resulting from mutp53 GOF. We discuss and stress the fact that the status of p53 currently constitutes one of the most relevant criteria to understand the role of autophagy as a survival mechanism in cancer, and propose new therapeutic approaches that could promote the reduction of GOF effects exercised by mutp53 in cancer.