Dichotomous transactivation domains contribute to growth inhibitory and promotion functions of TAp73.

The transcription factor p73, a member of the p53 tumor-suppressor family, regulates cell death and also supports tumorigenesis, although the mechanistic basis for the dichotomous functions is poorly understood. We report here the identification of an alternate transactivation domain (TAD) located at the extreme carboxyl (C) terminus of TAp73ß, a commonly expressed p73 isoform. Mutational disruption of this TAD significantly reduced TAp73ß's transactivation activity, to a level observed when the amino (N)-TAD that is similar to p53's TAD, is mutated. Mutation of both TADs almost completely abolished TAp73ß's transactivation activity. Expression profiling highlighted a unique set of targets involved in extracellular matrix-receptor interaction and focal adhesion regulated by the C-TAD, resulting in FAK phosphorylation, distinct from the N-TAD targets that are common to p53 and are involved in growth inhibition. Interestingly, the C-TAD targets are also regulated by the oncogenic, amino-terminal-deficient DNp73ß isoform. Consistently, mutation of C-TAD reduces cellular migration and proliferation. Mechanistically, selective binding of TAp73ß to DNAJA1 is required for the transactivation of C-TAD target genes, and silencing DNAJA1 expression abrogated all C-TAD-mediated effects. Taken together, our results provide a mechanistic basis for the dichotomous functions of TAp73 in the regulation of cellular growth through its distinct TADs.

DNA-delivered monoclonal antibodies targeting the p53 R175H mutant epitope inhibit tumor development in mice.

The tumor suppressor p53 is the most common mutated gene in cancer, with the R175H as the most frequent p53 missense mutant. However, there are currently no approved targeted therapies or immunotherapies against mutant p53. Here, we characterized and investigated a monoclonal antibody (mAb) that recognizes the mutant p53-R175H for its affinity, specificity, and activity against tumor cells in vitro. We then delivered DNA plasmids expressing the anti-R175H mAb or a bispecific antibody (BsAb) into mice to evaluate their therapeutic effects. Our results showed that the anti-R175H mAb specifically bound to the p53-R175H antigen with a high affinity and recognized the human mutant p53-R175H antigen expressed on HEK293T or MC38 cells, with no cross-reactivity with wild-type p53. In cultured cells, the anti-R175H mAb showed higher cytotoxicity than the control but did not induce antibody-dependent cellular cytotoxicity. We made a recombinant MC38 mouse cell line (MC38-p53-R175H) that overexpressed the human p53-R175H after knocking out the endogenous mutant p53 alleles. In vivo, administration of the anti-R175H mAb plasmid elicited a robust anti-tumor effect against MC38-p53-R175H in mice. The administration of the anti-R175H BsAb plasmid showed no therapeutic effects, yet potent anti-tumor activity was observed in combination with the anti-PD-1 antibody. These results indicate that targeting specific mutant epitopes using DNA-delivered mAbs or BsAbs presents a form of improved natural immunity derived from tumor-infiltrating B cells and plasma cells against intracellular tumor antigens.

Pushing the Frontiers of Cancer Research: Highlights from the Frontiers in Cancer Science Conference 2023.

The 15th annual Frontiers in Cancer Science (FCS) conference gathered scientific experts who shared the latest research converging upon several themes of cancer biology. These themes included the dysregulation of metabolism, cell death, and other signaling processes in cancer cells; using patient "omics" datasets and single-cell and spatial approaches to investigate heterogeneity, understand therapy resistance, and identify targets; innovative strategies for inhibiting tumors, including rational drug combinations and improved drug delivery mechanisms; and advances in models that can facilitate screening for cancer vulnerabilities and drug testing. We hope the insights from this meeting will stimulate further progress in the field.

Adipose-enriched peri-tumoral stroma, in contrast to myofibroblast-enriched stroma, prognosticates poorer survival in breast cancers.

Despite our understanding of the genetic basis of intra-tumoral heterogeneity, the role of stromal heterogeneity arising from an altered tumor microenvironment in affecting tumorigenesis is poorly understood. In particular, extensive study on the peri-tumoral stroma in the morphologically normal tissues surrounding the tumor is lacking. Here, we examine the heterogeneity in tumors and peri-tumoral stroma from 8 ER+/PR+/HER2- invasive breast carcinomas, through multi-region transcriptomic profiling by microarray. We describe the regional heterogeneity observed at the intrinsic molecular subtype, pathway enrichment, and cell type composition levels within each tumor and its peri-tumoral region, up to 7 cm from the tumor margins. Moreover, we identify a pro-inflammatory adipose-enriched peri-tumoral subtype which was significantly associated with poorer overall survival in breast cancer patients, in contrast to an adaptive immune cell- and myofibroblast-enriched subtype. These data together suggest that peri-tumoral heterogeneity may be an important determinant of the evolution and treatment of breast cancers.

JNK mediates cell death by promoting the ubiquitination of the apurinic/apyrimidinic endonuclease APE1.

The c-Jun-NH2-terminal kinases (JNKs) regulate cell death, generally through the direct phosphorylation of both pro- and anti-apoptotic substrates. In this report, we demonstrate an alternate mechanism of JNK-mediated cell death involving the anti-apoptotic protein human apurinic/apyrimidinic endonuclease 1 (APE1). Treatment of cells with a variety of genotoxic stresses enhanced APE1-JNK (all isoforms of JNK1 or JNK2) interaction, specifically in cells undergoing apoptosis. Steady-state APE1 levels were decreased in these cells, in which APE1 is ubiquitinated and degraded in a JNK-dependent manner. Absence of JNKs reduced APE1 ubiquitination and increased its abundance. Mechanistically, the E3 ligase ITCH associates with both APE1 and JNK and is necessary for JNK-dependent APE1 ubiquitination and degradation. Structural models of the JNK-APE1 interaction support the observation of enhanced association of the complex in the presence of ubiquitin. The data together show a mechanism of JNK-mediated cell death by the degradation of APE1 through ITCH.

BRAF(V600E) mutation together with loss of Trp53 or pTEN drives the origination of hairy cell leukemia from B-lymphocytes.

Hairy cell leukemia (HCL) is a B-lymphoma induced by BRAF(V600E) mutation. However, introducing BRAF(V600E) in B-lymphocytes fails to induce hematological malignancy, suggesting that BRAF(V600E) needs concurrent mutations to drive HCL ontogeny. To resolve this issue, here we surveyed human HCL genomic sequencing data. Together with previous reports, we speculated that the tumor suppressor TP53, P27, or PTEN restrict the oncogenicity of BRAF(V600E) in B-lymphocytes, and therefore that their loss-of-function facilitates BRAF(V600E)-driven HCL ontogeny. Using genetically modified mouse models, we demonstrate that indeed BRAF(V600E)KI together with Trp53KO or pTENKO in B-lymphocytes induces chronic lymphoma with pathological features of human HCL. To further understand the cellular programs essential for HCL ontogeny, we profiled the gene expression of leukemic cells isolated from BRAF(V600E)KI and Trp53KO or pTENKO mice, and found that they had similar but different gene expression signatures that resemble that of M2 or M1 macrophages. In addition, we examined the expression signature of transcription factors/regulators required for germinal center reaction and memory B cell versus plasma cell differentiation in these leukemic cells and found that most transcription factors/regulators essential for these programs were severely inhibited, illustrating why hairy cells are arrested at a transitional stage between activated B cells and memory B cells. Together, our study has uncovered concurrent mutations required for HCL ontogeny, revealed the B cell origin of hairy cells and investigated the molecular basis underlying the unique pathological features of the disease, with important implications for HCL research and treatment.

EPLIN-ß is a novel substrate of ornithine decarboxylase antizyme 1 and mediates cellular migration.

Polyamines promote cellular proliferation. Their levels are controlled by ornithine decarboxylase antizyme 1 (Az1, encoded by OAZ1), through the proteasome-mediated, ubiquitin-independent degradation of ornithine decarboxylase (ODC), the rate-limiting enzyme of polyamine biosynthesis. Az1-mediated degradation of other substrates such as cyclin D1 (CCND1), DNp73 (TP73) or Mps1 regulates cell growth and centrosome amplification, and the currently known six Az1 substrates are all linked with tumorigenesis. To understand whether Az1-mediated protein degradation might play a role in regulating other cellular processes associated with tumorigenesis, we employed quantitative proteomics to identify novel Az1 substrates. Here, we describe the identification of LIM domain and actin-binding protein 1 (LIMA1), also known as epithelial protein lost in neoplasm (EPLIN), as a new Az1 target. Interestingly, between the two EPLIN isoforms (α and ß), only EPLIN-ß is a substrate of Az1. The interaction between EPLIN-ß and Az1 appears to be indirect, and EPLIN-ß is degraded by Az1 in a ubiquitination-independent manner. Az1 absence leads to elevated EPLIN-ß levels, causing enhanced cellular migration. Consistently, higher LIMA1 levels correlate with poorer overall survival of colorectal cancer patients. Overall, this study identifies EPLIN-ß as a novel Az1 substrate regulating cellular migration.

Cancer Cells Shuttle Extracellular Vesicles Containing Oncogenic Mutant p53 Proteins to the Tumor Microenvironment.

Extracellular vesicles (EVs) shed by cancer cells play a major role in mediating the transfer of molecular information by reprogramming the tumor microenvironment (TME). TP53 (encoding the p53 protein) is the most mutated gene across many cancer types. Mutations in TP53 not only result in the loss of its tumor-suppressive properties but also results in the acquisition of novel gain-of-functions (GOF) that promote the growth of cancer cells. Here, we demonstrate that GOF mutant p53 proteins can be transferred via EVs to neighboring cancer cells and to macrophages, thus modulating them to release tumor supportive cytokines. Our data from pancreatic, lung, and colon carcinoma cell lines demonstrate that the mutant p53 protein can be selectively sorted into EVs. More specifically, mutant p53 proteins in EVs can be taken up by neighboring cells and mutant p53 expression is found in non-tumor cells in both human cancers and in non-human tissues in human xenografts. Our findings shed light on the intricate methods in which specific GOF p53 mutants can promote oncogenic mechanisms by reprogramming and then recruiting non-cancerous elements for tumor progression.

Corrigendum: The Contrived Mutant p53 Oncogene - Beyond Loss of Functions.

[This corrects the article DOI: 10.3389/fonc.2015.00276.].

MOAP-1-mediated dissociation of p62/SQSTM1 bodies releases Keap1 and suppresses Nrf2 signaling.

Nrf2 signaling is vital for protecting cells against oxidative stress. However, its hyperactivation is frequently found in liver cancer through excessive build-up of p62/SQSTM1 bodies that sequester Keap1, an adaptor of the E3-ubiquitin ligase complex for Nrf2. Here, we report that the Bax-binding protein MOAP-1 regulates p62-Keap1-Nrf2 signaling through disruption of p62 bodies. Upon induction of cellular stresses that stimulate formation of p62 bodies, MOAP-1 is recruited to p62 bodies and reduces their levels independent of the autophagy pathway. MOAP-1 interacts with the PB1-ZZ domains of p62 and interferes with its self-oligomerization and liquid-liquid phase separation, thereby disassembling the p62 bodies. Loss of MOAP-1 can lead to marked upregulation of p62 bodies, enhanced sequestration of Keap1 by p62 and hyperactivation of Nrf2 antioxidant target genes. MOAP-1-deficient mice exhibit an elevated tumor burden with excessive levels of p62 bodies and Nrf2 signaling in a diethylnitrosamine (DEN)-induced hepatocarcinogenesis model. Together, our data define MOAP-1 as a negative regulator of Nrf2 signaling via dissociation of p62 bodies.

Functional interaction between macrophages and hepatocytes dictate the outcome of liver fibrosis.

Hepatocytes and liver-resident macrophages known as Kupffer cells (KCs) are key cell types involved in liver fibrosis. The transcription factor c-Jun plays a fundamental role in regulating hepatocyte and macrophage functions. We have examined c-Jun's role in the functional interaction of these cells during liver fibrosis induced by carbon tetrachloride. While hepatocyte-specific c-jun deletion led to increased fibrosis, the opposite outcome was observed when c-jun was deleted in both hepatocytes and KCs. Molecular analyses revealed compromised cytokine gene expression as the apical event related to the phenotype. Yet, purified hepatocytes from both mouse cohorts showed similar defects in cytokine gene expression. However, we noted increased macrophage infiltration in the absence of c-Jun in hepatocytes, which when chemically depleted, reversed the phenotype. Consistently, c-jun deletion in KCs alone also led to reduced fibrosis and cytokine gene expression. By contrast, c-jun deletion in hepatocytes and KCs did not affect the resolution phase after fibrotic injury. These data together demonstrate a pro-fibrogenic role for c-Jun in hepatocytes and KCs that functionally interact to regulate liver fibrosis.

An Asian Body to Tackle Cancers in Asia - The Asian National Cancer Centers Alliance.

The socioeconomic burden of cancer is growing rapidly in the Asian region, with a concentrated burden on low- and middle- income countries. The residents of this region, representing almost 60% of the global population, demonstrate an eclectic and complex nature, with huge disparities in ethnicity, sociocultural practices among others. The Asian National Cancer Centers Alliance (ANCCA) was established in 2005 by heads of several national cancer centers (NCCs) in the region to address common issues and concerns among Asian countries. During the first 13 years of ANCCA's existence, the participating NCCs' senior managers paved the way toward collaboration through transparent sharing of key facts and activities. Concrete achievements of the Alliance include the Asia Tobacco-Free Declaration, the establishment of the ANCCA Constitution in 2014 as well as the creation of an official website more recently. In November 2019, the most active ANCCA members (China, India, Indonesia, Japan, Korea, Mongolia, Singapore, Thailand, and Vietnam) strengthened the bonds of the entity with the clear aim to halt the increase in cancer and mortality rates in Asian countries by 2030. New opportunities including accelerated cooperation between members as well as collaboration with external and multidisciplinary stakeholders at local, regional and international levels are an essential step to most effectively tackle cancers in Asia.

p53-Related Transcription Targets of TAp73 in Cancer Cells-Bona Fide or Distorted Reality?

Identification of p73 as a structural homolog of p53 fueled early studies aimed at determining if it was capable of performing p53-like functions. This led to a conundrum as p73 was discovered to be hardly mutated in cancers, and yet, TAp73, the full-length form, was found capable of performing p53-like functions, including transactivation of many p53 target genes in cancer cell lines. Generation of mice lacking p73/TAp73 revealed a plethora of developmental defects, with very limited spontaneous tumors arising only at a later stage. Concurrently, novel TAp73 target genes involved in cellular growth promotion that are not regulated by p53 were identified, mooting the possibility that TAp73 may have diametrically opposite functions to p53 in tumorigenesis. We have therefore comprehensively evaluated the TAp73 target genes identified and validated in human cancer cell lines, to examine their contextual relevance. Data from focused studies aimed at appraising if p53 targets are also regulated by TAp73-often by TAp73 overexpression in cell lines with non-functional p53-were affirmative. However, genome-wide and phenotype-based studies led to the identification of TAp73-regulated genes involved in cellular survival and thus, tumor promotion. Our analyses therefore suggest that TAp73 may not necessarily be p53's natural substitute in enforcing tumor suppression. It has likely evolved to perform unique functions in regulating developmental processes and promoting cellular growth through entirely different sets of target genes that are not common to, and cannot be substituted by p53. The p53-related targets initially reported to be regulated by TAp73 may therefore represent an experimental possibility rather than the reality.