TAp73 is required for macrophage-mediated innate immunity and the resolution of inflammatory responses

Decoding the immune landscape: a comprehensive analysis of immune-associated biomarkers in cervical carcinoma and their implications for immunotherapy strategies

Background and aims

Cervical cancer, a prevalent gynecological malignant tumor, poses a significant threat to women's health and lives. Immune checkpoint inhibitor (ICI) therapy has emerged as a promising avenue for treating cervical cancer. For patients with persistent or recurrent metastatic cervical cancer, If the sequence of dead receptor ligand-1 (PD-L1) is positive, ICI show significant clinical efficacy. PD-L1 expression serves as a valuable biomarker for assessing ICI therapeutic efficacy. However, the complex tumor immune microenvironment (TIME), encompassing immune cell composition and tumor-infiltrating lymphocyte (TIL) status, also exerts a profound influence on tumor immunity and prognosis. Given the remarkable strides made by ICI treatments in improving the survival rates of cervical cancer patients, it becomes essential to identify a comprehensive biomarker that integrates various TIME aspects to enhance the effectiveness of ICI treatment. Therefore, the quest for biomarkers linked to multiple facets of TIME in cervical cancer is a vital pursuit.

Methods

In this study, we have developed an Immune-Associated Gene Prognostic Index (IRGPI) with remarkable prognostic value specifically for cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC). The Cancer Genome Atlas CESC dataset (n = 305) was meticulously analyzed to pinpoint key immune-related genes via weighted gene co-expression network analysis and differential gene expression assays. Subsequently, we employed Cox regression analysis to construct the IRGPI. Furthermore, the composition of immune cells and TIL status were examined using CIBERSORT and TIDE. Tumor expression of Epigen, LCN10, and P73 were determined with immunohistochemistry.

Results

The resulting IRGPI, composed of EPGN, LCN10, and TP73 genes, displayed a strong negative correlation with patient survival. The discovery was validated with a patient cohort from our hospital. The IRGPI not only predicts the composition of immune cell subtypes such as Macrophages M1, NK cells, Mast cells, Plasma cells, Neutrophils, Dendritic cells, T cells CD8, and T cells CD4 within CESC, but also indicates TIL exclusion, dysfunction, and PD-1 and PD-L1 expression. Therefore, the IRGPI emerges as a promising biomarker not only for prognostic assessment but also for characterizing multiple immune features in CESC. Additionally, our results underscored the significant associations between the IRGPI and immune cell composition, TIL exclusion, and dysfunction, along with PD-1 and PD-L1 expression in the TIME.

Conclusion

Consequently, the IRGPI stands out as a biomarker intimately connected to both the survival and TIME status of CESC patients, offering potential insights into immunotherapy strategies for CESC.

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.

The c-Abl/p73 pathway induces neurodegeneration in a Parkinson's disease model

Parkinson's disease is the second most common neurodegenerative disorder. Although it is clear that dopaminergic neurons degenerate, the underlying molecular mechanisms are still unknown, and thus, successful treatment is still elusive. One pro-apoptotic pathway associated with several neurodegenerative diseases is the tyrosine kinase c-Abl and its target p73. Here, we evaluated the contribution of c-Abl and p73 in the degeneration of dopaminergic neurons induced by the neurotoxin 6-hydroxydopamine as a model for Parkinson's disease. First, we found that in SH-SY5Y cells treated with 6-hydroxydopamine, c-Abl and p73 phosphorylation levels were up-regulated. Also, we found that the pro-apoptotic p73 isoform TAp73 was up-regulated. Then, to evaluate whether c-Abl tyrosine kinase activity is necessary for 6-hydroxydopamine-induced apoptosis, we co-treated SH-SY5Y cells with 6-hydroxydopamine and Imatinib, a c-Abl specific inhibitor, observing that Imatinib prevented p73 phosphorylation, TAp73 up-regulation, and protected SH-SY5Y cells treated with 6-hydroxydopamine from apoptosis. Interestingly, this observation was confirmed in the c-Abl conditional null mice, where 6-hydroxydopamine stereotaxic injections induced a lesser reduction of dopaminergic neurons than in the wild-type mice significantly. Finally, we found that the intraperitoneal administration of Imatinib prevented the death of dopaminergic neurons induced by injecting 6-hydroxydopamine stereotaxically in the mice striatum. Thus, our findings support the idea that the c-Abl/p73 pathway is involved in 6-hydroxydopamine degeneration and suggest that inhibition of its kinase activity might be used as a therapeutical drug in Parkinson's disease.

Dual Role of p73 in Cancer Microenvironment and DNA Damage Response

Understanding the mechanisms that regulate cancer progression is pivotal for the development of new therapies. Although p53 is mutated in half of human cancers, its family member p73 is not. At the same time, isoforms of p73 are often overexpressed in cancers and p73 can overtake many p53 functions to kill abnormal cells. According to the latest studies, while p73 represses epithelial–mesenchymal transition and metastasis, it can also promote tumour growth by modulating crosstalk between cancer and immune cells in the tumor microenvironment, M2 macrophage polarisation, Th2 T-cell differentiation, and angiogenesis. Thus, p73 likely plays a dual role as a tumor suppressor by regulating apoptosis in response to genotoxic stress or as an oncoprotein by promoting the immunosuppressive environment and immune cell differentiation.

Mechanisms of Functional Pleiotropy of p73 in Cancer and Beyond

The transcription factor p73 is a structural and functional homolog of TP53, the most famous and frequently mutated tumor-suppressor gene. The TP73 gene can synthesize an overwhelming number of isoforms via splicing events in 5′ and 3′ ends and alternative promoter usage. Although it originally came into the spotlight due to the potential of several of these isoforms to mimic p53 functions, it is now clear that TP73 has its own unique identity as a master regulator of multifaceted processes in embryonic development, tissue homeostasis, and cancer. This remarkable functional pleiotropy is supported by a high degree of mechanistic heterogeneity, which extends far-beyond the typical mode of action by transactivation and largely relies on the ability of p73 isoforms to form protein–protein interactions (PPIs) with a variety of nuclear and cytoplasmic proteins. Importantly, each p73 isoform carries a unique combination of functional domains and residues that facilitates the establishment of PPIs in a highly selective manner. Herein, we summarize the expanding functional repertoire of TP73 in physiological and oncogenic processes. We emphasize how TP73’s ability to control neurodevelopment and neurodifferentiation is co-opted in cancer cells toward neoneurogenesis, an emerging cancer hallmark, whereby tumors promote their own innervation. By further exploring the canonical and non-canonical mechanistic patterns of p73, we apprehend its functional diversity as the result of a sophisticated and coordinated interplay of: (a) the type of p73 isoforms (b) the presence of p73 interaction partners in the cell milieu, and (c) the architecture of target gene promoters. We suppose that dysregulation of one or more of these parameters in tumors may lead to cancer initiation and progression by reactivating p73 isoforms and/or p73-regulated differentiation programs thereof in a spatiotemporally inappropriate manner. A thorough understanding of the mechanisms supporting p73 functional diversity is of paramount importance for the efficient and precise p73 targeting not only in cancer, but also in other pathological conditions where TP73 dysregulation is causally involved.

TAp73 represses NF-κB-mediated recruitment of tumor-associated macrophages in breast cancer

Breast cancer is one of the most prevalent cancers worldwide. Understanding this complex disease is therefore of great importance. Here, we report that loss of TAp73, a known tumor suppressor and member of the p53 protein family, leads to increased activation of the NF-κB pathway, secretion of the chemokine CCL2, and an increase in protumoral macrophage infiltration in human breast cancer. Both high levels of CCL2 and high macrophage infiltration are known to correlate with poor prognosis in breast cancer patients. This study identifies TAp73 as a regulator of macrophage recruitment and highlights a role for TAp73 in immune cell regulation in cancer.

Infiltration of tumor-promoting immune cells is a strong driver of tumor progression. Especially the accumulation of macrophages in the tumor microenvironment is known to facilitate tumor growth and to correlate with poor prognosis in many tumor types. TAp73, a member of the p53/p63/p73 family, acts as a tumor suppressor and has been shown to suppress tumor angiogenesis. However, what role TAp73 has in regulating immune cell infiltration is unknown. Here, we report that low levels of TAp73 correlate with an increased NF-κB–regulated inflammatory signature in breast cancer. Furthermore, we show that loss of TAp73 results in NF-κB hyperactivation and secretion of Ccl2, a known NF-κB target and chemoattractant for monocytes and macrophages. Importantly, TAp73-deficient tumors display an increased accumulation of protumoral macrophages that express the mannose receptor (CD206) and scavenger receptor A (CD204) compared to controls. The relevance of TAp73 expression in human breast carcinoma was further accentuated by revealing that TAp73 expression correlates negatively with the accumulation of protumoral CD163⁺ macrophages in breast cancer patient samples. Taken together, our findings suggest that TAp73 regulates macrophage accumulation and phenotype in breast cancer through inhibition of the NF-κB pathway.

Effect of 1-Carbaldehyde-3,4-dimethoxyxanthone on Prostate and HPV-18 Positive Cervical Cancer Cell Lines and on Human THP-1 Macrophages

Xanthone derivatives have shown promising antitumor properties, and 1-carbaldehyde-3,4-dimethoxyxanthone (1) has recently emerged as a potent tumor cell growth inhibitor. In this study, its effect was evaluated (MTT viability assay) against a new panel of cancer cells, namely cervical cancer (HeLa), androgen-sensitive (LNCaP) and androgen-independent (PC-3) prostate cancer, and nonsolid tumor derived cancer (Jurkat) cell lines. The effect of xanthone 1 on macrophage functions was also evaluated. The effect of xanthone 1-conditioned THP-1 human macrophage supernatants on the metabolic viability of cervical and prostate cancer cell lines was determined along with its interference with cytokine expression characteristic of M1 profile (IL-1 ≤ β; TNF-α) or M2 profile (IL-10; TGF-β) (PCR and ELISA). Nitric oxide (NO) production by murine RAW264.7 macrophages was quantified by Griess reaction. Xanthone 1 (20 μM) strongly inhibited the metabolic activity of the cell lines and was significantly more active against prostate cell lines compared to HeLa (p < 0.05). Jurkat was the cell most sensitive to the effect of xanthone 1. Compound 1-conditioned IL-4-stimulated THP-1 macrophage supernatants significantly (p < 0.05) inhibited the metabolic activity of HeLa, LNCaP, and PC-3. Xanthone 1 did not significantly affect the expression of cytokines by THP-1 macrophages. The inhibiting effect of compound 1 observed on the production of NO by RAW 264.7 macrophages was moderate. In conclusion, 1-carbaldehyde-3,4-dimethoxyxanthone (1) decreases the metabolic activity of cancer cells and seems to be able to modulate macrophage functions.

Tissue-specific roles of p73 in development and homeostasis

p73 (TP73) belongs to the p53 family of transcription factors. Its gene locus encodes two opposing types of isoforms, the transcriptionally active TAp73 class and the dominant-negative DNp73 class, which both play critical roles in development and homeostasis in an astonishingly diverse array of biological systems within specific tissues. While p73 has functions in cancer, this Review focuses on the non-oncogenic activities of p73. In the central and peripheral nervous system, both isoforms cooperate in complex ways to regulate neural stem cell survival, self-renewal and terminal differentiation. In airways, oviduct and to a lesser extent in brain ependyma, TAp73 is the master transcriptional regulator of multiciliogenesis, enabling fluid and germ cell transport across tissue surfaces. In male and female reproduction, TAp73 regulates gene networks that control cell-cell adhesion programs within germinal epithelium to enable germ cell maturation. Finally, p73 participates in the control of angiogenesis in development and cancer. While many open questions remain, we discuss here key findings that provide insight into the complex functions of this gene at the organismal, cellular and molecular level.

Crosstalk between TAp73 and TGF-β in fibroblast regulates iNOS expression and Nrf2-dependent gene transcription

Inducible nitric oxide synthase (iNOS) activity produces anti-tumor and anti-microbial effects but also promotes carcinogenesis through mutagenic, immunosuppressive and pro-angiogenic mechanisms. The tumor suppressor p53 contributes to iNOS downregulation by repressing induction of the NOS2 gene encoding iNOS, thereby limiting NO-mediated DNA damages. This study focuses on the role of the p53 homologue TAp73 in the regulation of iNOS expression. Induction of iNOS by immunological stimuli was upregulated in immortalized MEFs from TAp73^-/- mice, compared to TAp73^+/+ fibroblasts. This overexpression resulted both from increased levels of NOS2 transcripts, and from an increased stability of the protein. Limitation of iNOS expression by TAp73 in wild-type cells is alleviated by TGF-β receptor I inhibitors, suggesting a cooperation between TAp73 and TGF-β in suppression of iNOS expression. Accordingly, downregulation of iNOS expression by exogenous TGF-β1 was impaired in TAp73^-/- fibroblasts. Increased NO production in these cells resulted in a stronger, NO-dependent induction of Nrf2 target genes, indicating that the Nrf2-dependent adaptive response to nitrosative stress in fibroblasts is proportional to iNOS activity. NO-dependent induction of two HIF-1 target genes was also stronger in TAp73-deficient cells. Finally, the antimicrobial action of NO against Trypanosoma musculi parasites was enhanced in TAp73^-/- fibroblasts. Our data indicate that tumor suppressive TAp73 isoforms cooperate with TGF-β to control iNOS expression, NO-dependent adaptive responses to stress, and pathogen proliferation.

The p53 Family in Brain Disease

SIGNIFICANCE

The p53 family of transcription factors, including p53, p63, and p73, plays key roles in both biological and pathological processes, including cancer and neural development. Recent Advances: In recent years, a growing body of evidence has indicated that the entire p53 family is involved in the regulation of the central nervous system (CNS) functions as well as in the pathogenesis of several neurological disorders. Mechanistically, the p53 proteins control neuronal cell fate, terminal differentiation, and survival, via a complex interplay among the family members.

CRITICAL ISSUES

In this article, we discuss the involvement of the p53 family in neurobiology and in pathological conditions affecting the CNS, including neuroinflammation.

FUTURE DIRECTIONS

Understanding the molecular mechanism(s) underlying the function of the p53 family could improve our general knowledge of the pathogenesis of brain disorders and potentially pave the road for new therapeutic intervention. Antioxid. Redox Signal. 29, 1-14.

Non-oncogenic roles of TAp73: from multiciliogenesis to metabolism

The p53 family of transcription factors (p53, p63 and p73) covers a wide range of functions critical for development, homeostasis and health of mammals across their lifespan. Beside the well-established tumor suppressor role, recent evidence has highlighted novel non-oncogenic functions exerted by p73. In particular, p73 is required for multiciliated cell (MCC) differentiation; MCCs have critical roles in brain and airways to move fluids across epithelial surfaces and to transport germ cells in the reproductive tract. This novel function of p73 provides a unifying cellular mechanism for the disparate inflammatory and immunological phenotypes of p73-deficient mice. Indeed, mice with Trp73 deficiency suffer from hydrocephalus, sterility and chronic respiratory tract infections due to profound defects in ciliogenesis and complete loss of mucociliary clearance since MCCs are essential for cleaning airways from inhaled pollutants, pathogens and allergens. Cross-species genomic analyses and functional rescue experiments identify TAp73 as the master transcriptional integrator of ciliogenesis, upstream of previously known central nodes. In addition, TAp73 shows a significant ability to regulate cellular metabolism and energy production through direct transcriptional regulation of several metabolic enzymes, such as glutaminase-2 and glucose-6 phosphate dehydrogenase. This recently uncovered role of TAp73 in the regulation of cellular metabolism strongly affects oxidative balance, thus potentially influencing all the biological aspects associated with p73 function, including development, homeostasis and cancer. Although through different mechanisms, p63 isoforms also contribute to regulation of cellular metabolism, thus indicating a common route used by all family members to control cell fate. At the structural level, the complexity of p73's function is further enhanced by its ability to form heterotetramers with some p63 isoforms, thus indicating the existence of an intrafamily crosstalk that determines the global outcome of p53 family function. In this review, we have tried to summarize all the recent evidence that have emerged on the novel non-oncogenic roles of p73, in an attempt to provide a unified view of the complex function of this gene within its family.

TAp73 upregulates IL-1β in cancer cells: Potential biomarker in lung and breast cancer?

p73 is a transcription factor belonging to the p53 tumour suppressor family. p73^−/− mice exhibit a range of phenotypes including neurological, reproductive and inflammatory defects. Although the role of p73 in the control of genomic stability explains part of these phenotypes, a clear mechanism of how p73 participates in the inflammatory response is still elusive. Interleukin-1β (IL-1β) has a crucial role in mediating the inflammatory response. Because of its high potency to induce inflammation, the activation and secretion of IL-1β is tightly regulated by large protein complexes, named inflammasomes. Inflammasomes regulate activation of proinflammatory caspase-1, which in turn proteolytically processes its substrates, including pro-IL-1β. Caspase-1 gene transcription is strongly activated by p53 protein family members including p73. Here, we have addressed whether p73 might be directly involved in IL-1β regulation and therefore in the control of the inflammatory response. Our results show that TAp73β upregulates pro-IL-1β mRNA and processed IL-1β protein. In addition, analysis of breast and lung cancer patient cohorts demonstrated that interaction between p73 and IL-1β predicts a negative survival outcome in these human cancers.

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The p53 family member p73 controls a wide a range of biological processes required for its tumour suppressor functions.

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p73 regulates IL-1β expression, thus potentially affecting inflammasomes and inflammatory response.

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p73/IL-1β axis correlates with poor prognosis in lung and breast cancer.

DNA repair and aging: the impact of the p53 family

Cells are constantly exposed to endogenous and exogenous factors that threaten the integrity of their DNA. The maintenance of genome stability is of paramount importance in the prevention of both cancer and aging processes. To deal with DNA damage, cells put into operation a sophisticated and coordinated mechanism, collectively known as DNA damage response (DDR). The DDR orchestrates different cellular processes, such as DNA repair, senescence and apoptosis. Among the key factors of the DDR, the related proteins p53, p63 and p73, all belonging to the same family of transcription factors, play multiple relevant roles. Indeed, the members of this family are directly involved in the induction of cell cycle arrest that is necessary to allow the cells to repair. Alternatively, they can promote cell death in case of prolonged or irreparable DNA damage. They also take part in a more direct task by modulating the expression of core factors involved in the process of DNA repair or by directly interacting with them. In this review we will analyze the fundamental roles of the p53 family in the aging process through their multifaceted function in DDR.

p73 regulates basal and starvation-induced liver metabolism in vivo

As a member of the p53 gene family, p73 regulates cell cycle arrest, apoptosis, neurogenesis, immunity and inflammation. Recently, p73 has been shown to transcriptionally regulate selective metabolic enzymes, such as cytochrome c oxidase subunit IV isoform 1, glucose 6-phosphate dehydrogenase and glutaminase-2, resulting in significant effects on metabolism, including hepatocellular lipid metabolism, glutathione homeostasis and the pentose phosphate pathway. In order to further investigate the metabolic effect of p73, here, we compared the global metabolic profile of livers from p73 knockout and wild-type mice under both control and starvation conditions. Our results show that the depletion of all p73 isoforms cause altered lysine metabolism and glycolysis, distinct patterns for glutathione synthesis and Krebs cycle, as well as an elevated pentose phosphate pathway and abnormal lipid accumulation. These results indicate that p73 regulates basal and starvation-induced fuel metabolism in the liver, a finding that is likely to be highly relevant for metabolism-associated disorders, such as diabetes and cancer.

Resolution of inflammation: a new therapeutic frontier

Dysregulated inflammation is a central pathological process in diverse disease states. Traditionally, therapeutic approaches have sought to modulate the pro- or anti-inflammatory limbs of inflammation, with mixed success. However, insight into the pathways by which inflammation is resolved has highlighted novel opportunities to pharmacologically manipulate these processes - a strategy that might represent a complementary (and perhaps even superior) therapeutic approach. This Review discusses the state of the art in the biology of resolution of inflammation, highlighting the opportunities and challenges for translational research in this field.

TAp73 loss favors Smad-independent TGF-β signaling that drives EMT in pancreatic ductal adenocarcinoma

Advances made in pancreatic cancer therapy have been far from sufficient and have allowed only a slight improvement in global survival of patients with pancreatic ductal adenocarcinoma (PDA). Recent progresses in chemotherapy have offered some hope for an otherwise gloomy outlook, however, only a limited number of patients are eligible because of important cytotoxicity. In this context, enhancing our knowledge on PDA initiation and evolution is crucial to highlight certain weaknesses on which to specifically target therapy. We found that loss of transcriptionally active p73 (TAp73), a p53 family member, impacted PDA development. In two relevant and specific engineered pancreatic cancer mouse models, we observed that TAp73 deficiency reduced survival and enhanced epithelial-to-mesenchymal transition (EMT). Through proteomic analysis of conditioned media from TAp73 wild-type (WT) and deficient pancreatic tumor cells, we identified a secreted protein, biglycan (BGN), which is necessary and sufficient to mediate this pro-EMT effect. Interestingly, BGN is modulated by and modulates the transforming growth factor-β (TGF-β) pathway, a key regulator of the EMT process. We further examined this link and revealed that TAp73 impacts the TGF-β pathway by direct regulation of BGN expression and Sma and Mad-related proteins (SMADs) expression/activity. Absence of TAp73 leads to activation of TGF-β signaling through a SMAD-independent pathway, favoring oncogenic TGF-β effects and EMT. Altogether, our data highlight the implication of TAp73 in the aggressiveness of pancreatic carcinogenesis through modulation of the TGF-β signaling. By suggesting TAp73 as a predictive marker for response to TGF-β inhibitors, our study could improve the classification of PDA patients with a view to offering combined therapy involving TGF-β inhibitors.

Neuroblastoma: oncogenic mechanisms and therapeutic exploitation of necroptosis

Neuroblastoma (NB) is the most common extracranial childhood tumor classified in five stages (1, 2, 3, 4 and 4S), two of which (3 and 4) identify chemotherapy-resistant, highly aggressive disease. High-risk NB frequently displays MYCN amplification, mutations in ALK and ATRX, and genomic rearrangements in TERT genes. These NB subtypes are also characterized by reduced susceptibility to programmed cell death induced by chemotherapeutic drugs. The latter feature is a major cause of failure in the treatment of advanced NB patients. Thus, proper reactivation of apoptosis or of other types of programmed cell death pathways in response to treatment is relevant for the clinical management of aggressive forms of NB. In this short review, we will discuss the most relevant genomic rearrangements that define high-risk NB and the role that destabilization of p53 and p73 can have in NB aggressiveness. In addition, we will propose a strategy to stabilize p53 and p73 by using specific inhibitors of their ubiquitin-dependent degradation. Finally, we will introduce necroptosis as an alternative strategy to kill NB cells and increase tumor immunogenicity.

p63 threonine phosphorylation signals the interaction with the WW domain of the E3 ligase Itch

Both in epithelial development as well as in epithelial cancers, the p53 family member p63 plays a crucial role acting as a master transcriptional regulator. P63 steady state protein levels are regulated by the E3 ubiquitin ligase Itch, via a physical interaction between the PPxY consensus sequence (PY motif) of p63 and one of the 4 WW domains of Itch; this substrate recognition process leads to protein-ubiquitylation and p63 proteasomal degradation. The interaction of the WW domains, a highly compact protein-protein binding module, with the short proline-rich sequences is therefore a crucial regulatory event that may offer innovative potential therapeutic opportunity. Previous molecular studies on the Itch-p63 recognition have been performed in vitro using the Itch-WW2 domain and the peptide interacting fragment of p63 (pep63), which includes the PY motif. Itch-WW2-pep63 interaction is also stabilized in vitro by the conformational constriction of the S-S cyclization in the p63 peptide. The PY motif of p63, as also for other proteins, is characterized by the nearby presence of a (T/S)P motif, which is a potential recognition site of the WW domain of the IV group present in the prolyl-isomerase Pin1. In this study, we demonstrate, by in silico and spectroscopical studies using both the linear pep63 and its cyclic form, that the threonine phosphorylation of the (T/S)PPPxY motif may represent a crucial regulatory event of the Itch-mediated p63 ubiquitylation, increasing the Itch-WW domains-p63 recognition event and stabilizing in vivo the Itch-WW-p63 complex. Moreover, our studies confirm that the subsequently trans/cis proline isomerization of (T/S)P motif by the Pin1 prolyl-isomerase, could modulate the E3-ligase interaction, and that the (T/S)pPtransPPxY motif represent the best conformer for the ItchWW-(T/S)PPPxY motif recognition.

How Does p73 Cause Neuronal Defects?

The p53-family member, p73, plays a key role in the development of the central nervous system (CNS), in senescence, and in tumor formation. The role of p73 in neuronal differentiation is complex and involves several downstream pathways. Indeed, in the last few years, we have learnt that TAp73 directly or indirectly regulates several genes involved in neural biology. In particular, TAp73 is involved in the maintenance of neural stem/progenitor cell self-renewal and differentiation throughout the regulation of SOX-2, Hey-2, TRIM32 and Notch. In addition, TAp73 is also implicated in the regulation of the differentiation and function of postmitotic neurons by regulating the expression of p75NTR and GLS2 (glutamine metabolism). Further still, the regulation of miR-34a by TAp73 indicates that microRNAs can also participate in this multifunctional role of p73 in adult brain physiology. However, contradictory results still exist in the relationship between p73 and brain disorders, and this remains an important area for further investigation.

Screening for E3-ubiquitin ligase inhibitors: challenges and opportunities

The ubiquitin proteasome system (UPS) plays a role in the regulation of most cellular pathways, and its deregulation has been implicated in a wide range of human pathologies that include cancer, neurodegenerative and immunological disorders and viral infections. Targeting the UPS by small molecular regulators thus provides an opportunity for the development of therapeutics for the treatment of several diseases. The proteasome inhibitor Bortezomib was approved for treatment of hematologic malignancies by the FDA in 2003, becoming the first drug targeting the ubiquitin proteasome system in the clinic. Development of drugs targeting specific components of the ubiquitin proteasome system, however, has lagged behind, mainly due to the complexity of the ubiquitination reaction and its outcomes. However, significant advances have been made in recent years in understanding the molecular nature of the ubiquitination system and the vast variety of cellular signals that it produces. Additionally, improvement of screening methods, both in vitro and in silico, have led to the discovery of a number of compounds targeting components of the ubiquitin proteasome system, and some of these have now entered clinical trials. Here, we discuss the current state of drug discovery targeting E3 ligases and the opportunities and challenges that it provides.

Polycomb-mediated loss of microRNA let-7c determines inflammatory macrophage polarization via PAK1-dependent NF-κB pathway

Serine/threonine kinase family members p21-activated kinases (PAKs) are important regulators of cytoskeletal remodeling and cell motility in mononuclear phagocytic system, but their role in macrophage differentiation and polarization remains obscure. We have shown here that inflammatory stimuli induced PAK1 overexpression in human and murine macrophages. Elevated expression of PAK1 contributed to macrophage M1 polarization and lipopolysaccharide (LPS)-induced endotoxin shock. We further observed that epigenetic loss of microRNA let-7c due to enhancer of zeste homolog 2 (EZH2) upregulation determined PAK1 elevation and inflammatory phenotype in M1 macrophages. EZH2/let-7c/PAK1 axis promotes macrophage M1 polarization via NIK-IKK-NF-κB signaling. Moreover, pharmacological and genetic ablation with EZH2/let-7c/PAK1 axis blunted inflammatory phenotype in M1 macrophages. Critically, either myeloid-restricted PAK1 deletion (PAK1(Lyz2cre)) or pharmacological and genetic ablation with EZH2/let-7c/PAK1 signal resulted in resistance to LPS-induced endotoxin shock via blunting macrophage M1 polarization. PAK1, therefore, is an essential controller of inflammatory macrophage polarization, regulating immune responses against pathogenic stimuli.

Functions, divergence and clinical value of TAp73 isoforms in cancer

The p73 gene encodes the tumour suppressive full-length TAp73 and N-terminal-truncated DNp73 isoforms that act as dominant negative inhibitors of TAp73. The overall effect of p73 in oncogenesis is thought to depend on the TAp73 to DNp73 isoforms' ratio. TAp73 isoforms include a number of C-terminal variants as a result of alternative splicing in 3'-end. TAp73 isoforms protect cells from oncogenic alterations in a multifaceted way since they are implicated in the suppression of all demonstrated hallmarks and enabling characteristics of cancer. Their best established role is in apoptosis, a process which seems to be differently affected by each TAp73 C-terminal variant. Based on previous findings and our thorough bioinformatics analysis, we highlight that TAp73 variants are functionally non-equivalent, since they present major differences in their transactivation efficiencies, protein interactions, response to DNA damage and apoptotic effects that are attributable to the primary structure of their C terminus. In this review, we summarise these differences and we unveil the link between crucial C-terminal motifs/residues and the oncosuppressive potential of TAp73 isoforms, emphasising on the importance of considering C terminus during the development of p73-based anticancer biologics.

TP63 and TP73 in cancer, an unresolved "family" puzzle of complexity, redundancy and hierarchy

TP53 belongs to a small gene family that includes, in mammals, two additional paralogs, TP63 and TP73. The p63 and p73 proteins are structurally and functionally similar to p53 and their activity as transcription factors is regulated by a wide repertoire of shared and unique post-translational modifications and interactions with regulatory cofactors. p63 and p73 have important functions in embryonic development and differentiation but are also involved in tumor suppression. The biology of p63 and p73 is complex since both TP63 and TP73 genes are transcribed into a variety of different isoforms that give rise to proteins with antagonistic properties, the TA-isoforms that act as tumor-suppressors and DN-isoforms that behave as proto-oncogenes. The p53 family as a whole behaves as a signaling "network" that integrates developmental, metabolic and stress signals to control cell metabolism, differentiation, longevity, proliferation and death. Despite the progress of our knowledge, the unresolved puzzle of complexity, redundancy and hierarchy in the p53 family continues to represent a formidable challenge.

Enhancement of CD147 on M1 macrophages induces differentiation of Th17 cells in the lung interstitial fibrosis

Lung interstitial fibrosis is a chronic lung disease, and few effective therapies are available to halt or reverse the progression of the disease. In murine and human lung fibrosis, the expression of CD147 is increased. However, the role of CD147 in lung fibrosis has not been identified, and it remains to be determined whether lung fibrosis would be improved by decreasing the expression of CD147. A murine bleomycin-induced lung interstitial fibrosis model was used in the experiments, and HAb18 mAbs and CsA were administered during the induction of lung fibrosis. In our study, we found that the HAb18 mAbs markedly reduced the collagen score and down-regulated M1 macrophages and Th17 cells. In vitro, flow cytometry analysis showed that M1 macrophages induced higher Th17 differentiation than M2 macrophages. After treatment with HAb18 mAbs or after reducing the expression of CD147 by lentivirus interference in M1 macrophages, the level of Th17 cells were significantly inhibited. In conclusion, HAb18 mAbs or CsA treatment ameliorates lung interstitial fibrosis. CD147 promoted M1 macrophage and induced the differentiation of Th17 cells in lung interstitial fibrosis, perhaps by regulating some cytokines such as IL-6, IL-1β, IL-12 and IL-23. These results indicated that CD147 may play an important role in the development of lung interstitial fibrosis.

ITCH deficiency protects from diet-induced obesity

Classically activated macrophages (M1) secrete proinflammatory cytokine and are predominant in obese adipose tissue. M2 macrophages, prevalent in lean adipose tissue, are induced by IL-13 and IL-4, mainly secreted by Th2 lymphocytes, and produce the anti-inflammatory cytokine IL-10. ITCH is a ubiquitously expressed E3 ubiquitin ligase involved in T-cell differentiation and in a wide range of inflammatory pathways. ITCH downregulation in lymphocytes causes aberrant Th2 differentiation. To investigate the role of Th2/M2 polarization in obesity-related inflammation and insulin resistance, we compared wild-type and Itch(-/-) mice in a context of diet-induced obesity (high-fat diet [HFD]). When subjected to HFD, Itch(-/-) mice did not show an increase in body weight or insulin resistance; calorimetric analysis suggested an accelerated metabolism. The molecular analysis of metabolically active tissue revealed increased levels of M2 markers and genes involved in fatty acid oxidation. Histological examination of livers from Itch(-/-) mice suggested that ITCH deficiency protects mice from obesity-related nonalcoholic fatty liver disease. We also found a negative correlation between ITCH and M2 marker expression in human adipose tissues. Taken together, our data indicate that ITCH E3 ubiquitin ligase deficiency protects from the metabolic disorder caused by obesity.

Senescence and aging: the critical roles of p53

p53 functions as a transcription factor involved in cell-cycle control, DNA repair, apoptosis and cellular stress responses. However, besides inducing cell growth arrest and apoptosis, p53 activation also modulates cellular senescence and organismal aging. Senescence is an irreversible cell-cycle arrest that has a crucial role both in aging and as a robust physiological antitumor response, which counteracts oncogenic insults. Therefore, via the regulation of senescence, p53 contributes to tumor growth suppression, in a manner strictly dependent by its expression and cellular context. In this review, we focus on the recent advances on the contribution of p53 to cellular senescence and its implication for cancer therapy, and we will discuss p53's impact on animal lifespan. Moreover, we describe p53-mediated regulation of several physiological pathways that could mediate its role in both senescence and aging.

Tumor suppressor WWOX binds to ΔNp63α and sensitizes cancer cells to chemotherapy

The WWOX tumor suppressor is a WW domain-containing protein. Its function in the cell has been shown to be mediated, in part, by interacting with its partners through its first WW (WW1) domain. Here, we demonstrated that WWOX via WW1 domain interacts with p53 homolog, ΔNp63α. This protein–protein interaction stabilizes ΔNp63α, through antagonizing function of the E3 ubiquitin ligase ITCH, inhibits nuclear translocation of ΔNp63α into the nucleus and suppresses ΔNp63α transactivation function. Additionally, we found that this functional crosstalk reverses cancer cells resistance to cisplatin, mediated by ΔNp63α, and consequently renders these cells more sensitive to undergo apoptosis. These findings suggest a functional crosstalk between WWOX and ΔNp63α in tumorigenesis.