Expression and regulation of the ΔN and TAp63 isoforms in salivary gland tumorigenesis clinical and experimental findings

Dysregulation of delta Np63 alpha in squamous cell carcinoma and its therapeutic targeting

The gene p63 has two isoforms -a full length transactivated isoform (TA) p63 and an amino-terminally truncated isoform, ∆Np63. DeltaNp63 alpha (∆Np63α) is the predominant splice variant of the isoform, ∆Np63 and is expressed in the basal layer of stratified epithelia. ∆Np63α that is normally essential for the epithelial lineage maintenance may be dysregulated in squamous cell carcinomas (SCCs). The pro-tumorigenic or antitumorigenic role of ∆Np63 is a highly contentious arena. ∆Np63α may act as a double-edged sword. It may either promote tumor progression, epithelial-mesenchymal transition, migration, chemoresistance, and immune-inflammatory responses, or inhibit the aforementioned phenomena depending upon cell type and tumor microenvironment. Several signaling pathways, transforming growth factor-β, Wnt and Notch, as well as epigenetic alterations involving microRNAs, and long noncoding RNAs are regulated by ∆Np63α. This review has attempted to provide an in-depth insight into the role of ∆Np63α in the development of SCCs during different stages of tumor formation and how it may be targeted for therapeutic implications.

ΔNp63 overexpression promotes oral cancer cell migration through hyperactivated Activin A signaling

Oral cancer is a common malignant tumor of the oral cavity that affects many countries with a prevalent distribution in the Indian subcontinent, with poor prognosis rate on account of locoregional metastases. Gain-of-function mutations in p53 and overexpression of its related transcription factor, p63 are both widely reported events in oral cancers. However, targeting these alterations remains a far-achieved aim due to lack of knowledge on their downstream signaling pathways. In the present study, we characterize the isoforms of p63 and using knockdown strategy, decipher the functions and oncogenic signaling of p63 in oral cancers. Using Microarray and Chromatin Immunoprecipitation experiments, we decipher a novel transcriptional regulatory axis between p63 and Activin A and establish its functional significance in migration of oral cancer cells. Using an orally bioavailable inhibitor of the Activin A pathway to attenuate oral cancer cell migration and invasion, we further demonstrate the targetability of this signaling axis. Our study highlights the oncogenic role of ΔNp63 - Activin A - SMAD2/3 signaling and provides a basis for targeting this oncogenic pathway in oral cancers.

Postnatal changes in the development of rat submandibular glands in offspring of diabetic mothers: Biochemical, histological and ultrastructural study

Development and maturation of submandibular salivary glands are influenced by intrauterine diabetic environment. Several studies investigated the effects of diabetes on the salivary glands. However, the effects of maternal diabetes on the submandibular glands of the offspring was not properly examined. Therefore, the present study was designed to describe the changes in the development of the submandibular glands of the offspring of diabetic mothers. The submandibular glands of the offspring of Streptozotocin (STZ)-induced diabetic female rats were examined at two and four weeks after birth. Detection of mRNA demonstrated that maternal diabetes affects the level of different indicators. The reduction of expression of epidermal growth factor (EGF); a protein mitogen, cytokeratin 5 (CK5); an epithelial cell progenitor, CK7 and aquaporin 5 (AQP5); differentiation markers and B cell lymphoma 2 (Bcl2); an antiapoptotic marker were found. Increase in Bcl2-associated X protein (Bax); an apoptotic marker was detected. These changes indicate their effects on saliva secretion, glands tumorigenesis, growth of normal oral flora and oral microbes, with decreased protein synthesis and production of xerostomia and dental caries. Loss of normal glandular architecture, significant increase in fibrosis, by the detection of collagen fibers, and stagnation of secretory granules were found with atrophic changes in the acinar cells. Marked defect of polysaccharides in the acinar cells, denoting functional changes, was manifested by significant reduction of the intensity of periodic acid-Schiff (PAS) reaction. The positive immunoreactivity of caspase-3, denoting cellular apoptosis, and minimal reaction of alpha-smooth muscle actin (α SMA) and proliferating cell nuclear antigen (PCNA) were evident in the offspring of diabetic mothers. We conclude that maternal diabetes produces degenerative effects in the structure and function of the submandibular salivary glands of the offspring, reflecting possible influences on their secretory activity affecting oral and digestive health.

p63 isoforms in triple-negative breast cancer: ΔNp63 associates with the basal phenotype whereas TAp63 associates with androgen receptor, lack of BRCA mutation, PTEN and improved survival

The TP63 gene encodes two major protein variants that differ in their N-terminal sequences and have opposing effects. In breast, ΔNp63 is expressed by immature stem/progenitor cells and mature myoepithelial/basal cells and is a characteristic feature of basal-like triple-negative breast cancers (TNBCs). The expression and potential role of TAp63 in the mammary gland and breast cancers is less clear, partly due to the lack of studies that employ p63 isoform-specific antibodies. We used immunohistochemistry with ΔNp63-specific or TAp63-specific monoclonal antibodies to investigate p63 isoforms in 236 TNBCs. TAp63, but not ΔNp63, was seen in tumour-associated lymphocytes and other stromal cells. Tumour cells showed nuclear staining for ΔNp63 in 17% of TNBCs compared to 7.3% that were positive for TAp63. Whilst most TAp63⁺ tumours also contained ΔNp63⁺ cells, the levels of the two isoforms were independent of each other. ΔNp63 associated with metaplastic and medullary cancers, and with a basal phenotype, whereas TAp63 associated with androgen receptor, BRCA1/2 wild-type status and PTEN positivity. Despite the proposed effects of p63 on proliferation, Ki67 did not correlate with either p63 isoform, nor did they associate with p53 mutation status. ΔNp63 showed no association with patient outcomes, whereas TAp63⁺ patients showed fewer recurrences and improved overall survival. These findings indicate that both major p63 protein isoforms are expressed in TNBCs with different tumour characteristics, indicating distinct functional activities of p63 variants in breast cancer. Analysis of individual p63 isoforms provides additional information into TNBC biology, with TAp63 expression indicating improved prognosis.

An oncogenic MYB feedback loop drives alternate cell fates in adenoid cystic carcinoma

Translocation events are frequent in cancer and may create chimeric fusions or ‘regulatory rearrangements’ that drive oncogene overexpression. Here we identify super-enhancer translocations that drive overexpression of the oncogenic transcription factor MYB as a recurrent theme in adenoid cystic carcinoma (ACC). Whole-genome sequencing data and chromatin maps reveal distinct chromosomal rearrangements that juxtapose super-enhancers to the MYB locus. Chromosome conformation capture confirms that the translocated enhancers interact with the MYB promoter. Remarkably, MYB protein binds to the translocated enhancers, creating a positive feedback loop that sustains its expression. MYB also binds enhancers that drive different regulatory programs in alternate cell lineages in ACC, cooperating with TP63 in myoepithelial cells and a Notch program in luminal epithelial cells. Bromodomain inhibitors slow tumor growth in ACC primagraft models in vivo. Thus, our study identifies super-enhancer translocations that drive MYB expression and provides insight into downstream MYB functions in the alternate ACC lineages.

The microRNA feedback regulation of p63 in cancer progression

The transcription factor p63 is a member of the p53 gene family that plays a complex role in cancer due to its involvement in epithelial differentiation, cell cycle arrest and apoptosis. MicroRNAs are a class of small, non-coding RNAs with an important regulatory role in various cellular processes, as well as in the development and progression of cancer. A number of microRNAs have been shown to function as transcriptional targets of p63. Conversely, microRNAs also can modulate the expression and activity of p63. However, the p63-microRNA regulatory circuit has not been addressed in depth so far. Here, computational genomic analysis was performed using miRtarBase, Targetscan, microRNA.ORG, DIANA-MICROT, RNA22-HSA and miRDB to analyze miRNA binding to the 3'UTR of p63. JASPAR (profile score threshold 80%) and TFSEARCH datasets were used to search transcriptional start sites for p53/p63 response elements. Remarkably, these data revealed 63 microRNAs that targeted p63. Furthermore, there were 39 microRNAs targeting p63 that were predicted to be regulated by p63. These analyses suggest a crosstalk between p63 and microRNAs. Here, we discuss the crosstalk between p63 and the microRNA network, and the role of their interactions in cancer.

A comparative immunohistochemistry study of diagnostic tools in salivary gland tumors: usefulness of mammaglobin, gross cystic disease fluid protein 15, and p63 cytoplasmic staining for the diagnosis of mammary analog secretory carcinoma?

BACKGROUND

Mammary analog secretory carcinoma (MASC) of the salivary gland has been recently described according to morphological, immunohistochemical, and molecular (ETV6-NTRK3 translocation) similarities with the mammary secretory carcinoma. The most important differential diagnostic considerations of MASC are low-grade adenocarcinoma not otherwise specified (NOS), cystadenocarcinoma, and acinic cell carcinoma (AciCC). These tumors may share an overlapping morphology with MASC, and additional immunohistochemical studies are required to reinforce the diagnosis. Mammaglobin, GCDFP-15, and p63 staining have been reported in MASC. Our study was designed to check the specificity of these antibodies in MASC compared to other frequent tumors of salivary glands.

METHODS

A series of 62 salivary gland tumors [10 MASCs, 5 adenocarcinomas NOS and 2 cystadenocarcinomas with MASC features and without ETV6 rearrangement, one low-grade cribriform cystadenocarcinoma (LGCCC), 9 AciCCs, 10 MECs, 10 adenoid cystic carcinomas (AdeCCs), 5 polymorphous low-grade adenocarcinomas (PLGAs), and 10 pleomorphic adenomas (PAs)] was analyzed by immunohistochemistry with mammaglobin, GCDFP-15, and p63 antibodies.

RESULTS

Positivity for mammaglobin was observed in all MASCs, cystadenocarcinomas, LGCCC, and PLGAs, in some adenocarcinomas NOS, PAs, and MECs, rarely in AciCCs and never in AdeCCs. Positivity for GCDFP-15 was observed in most of the tumor types except in AdeCCs. Interestingly, cytoplasmic positivity for p63 was observed in most of MASCs and PLGAs while rarely in adenocarcinomas NOS and PAs, and never in the other tumor types.

CONCLUSION

Our study revealed the usefulness of mammaglobin and p63 cytoplasmic staining to define which tumors are worth to be screened for ETV6 rearrangement.

Role of the p63-FoxN1 regulatory axis in thymic epithelial cell homeostasis during aging

The p63 gene regulates thymic epithelial cell (TEC) proliferation, whereas FoxN1 regulates their differentiation. However, their collaborative role in the regulation of TEC homeostasis during thymic aging is largely unknown. In murine models, the proportion of TAp63(+), but not ΔNp63(+), TECs was increased with age, which was associated with an age-related increase in senescent cell clusters, characterized by SA-β-Gal(+) and p21(+) cells. Intrathymic infusion of exogenous TAp63 cDNA into young wild-type (WT) mice led to an increase in senescent cell clusters. Blockade of TEC differentiation via conditional FoxN1 gene knockout accelerated the appearance of this phenotype to early middle age, whereas intrathymic infusion of exogenous FoxN1 cDNA into aged WT mice brought only a modest reduction in the proportion of TAp63(+) TECs, but an increase in ΔNp63(+) TECs in the partially rejuvenated thymus. Meanwhile, we found that the increased TAp63(+) population contained a high proportion of phosphorylated-p53 TECs, which may be involved in the induction of cellular senescence. Thus, TAp63 levels are positively correlated with TEC senescence but inversely correlated with expression of FoxN1 and FoxN1-regulated TEC differentiation. Thereby, the p63-FoxN1 regulatory axis in regulation of postnatal TEC homeostasis has been revealed.

P63 expression in papillary cystadenoma and mucoepidermoid carcinoma of minor salivary glands

OBJECTIVE

The aim of this study was to investigate the expression of p63 protein in mucoepidermoid carcinoma and papillary cystadenoma of the salivary glands, and to evaluate the usefulness of this protein in distinguishing these tumors.

STUDY DESIGN

Immunoexpression of p63 protein was studied and quantified in 9 formalin-fixed paraffin-embedded mucous retention cysts, 4 papillary cystadenomas, and 19 low-grade and 9 high-grade mucoepidermoid carcinomas.

RESULTS

All cases were positive for p63 immunoexpression; however, it was observed that p63 labeling in mucous retention cysts and papillary cystadenomas was limited to the basal layers of the cystic spaces, whereas in low-grade mucoepidermoid carcinomas, positive nuclear staining was also found diffusely in the suprabasal layers. Mucoepidermoid carcinoma presented increased immunoexpression of p63 compared with the other groups.

CONCLUSIONS

P63 immunohistochemical expression pattern can be helpful in distinguishing low-grade mucoepidermoid carcinoma from papillary cystadenoma of the salivary glands.

15-hydroxyprostaglandin dehydrogenase-derived 15-keto-prostaglandin E2 inhibits cholangiocarcinoma cell growth through interaction with peroxisome proliferator-activated receptor-γ, SMAD2/3, and TAP63 proteins

Prostaglandin E2 (PGE2) is a potent lipid mediator that plays a key role in inflammation and carcinogenesis. NAD(+)-dependent 15-hydroxyprostaglandin dehydrogenase (15-PGDH) catalyzes the oxidation of the 15(S)-hydroxyl group of PGE2, which leads to PGE2 biotransformation. In this study, we showed that the 15-PGDH-derived 15-keto-PGE2 is an endogenous peroxisome proliferator-activated receptor-γ (PPAR-γ) ligand that causes PPAR-γ dissociation from Smad2/3, allowing Smad2/3 association with the TGF-β receptor I and Smad anchor for receptor activation and subsequent Smad2/3 phosphorylation and transcription activation in human cholangiocarcinoma cells. The 15-PGDH/15-keto-PGE2-induced Smad2/3 phosphorylation resulted in the formation of the pSmad2/3-TAP63-p53 ternary complex and their binding to the TAP63 promoter, inducing TAP63 autotranscription. The role of TAP63 in 15-PGDH/15-keto-PGE2-induced inhibition of tumor growth was further supported by the observation that knockdown of TAP63 prevented 15-PGDH-induced inhibition of tumor cell proliferation, colony formation, and migration. These findings disclose a novel 15-PGDH-mediated 15-keto-PGE2 signaling cascade that interacts with PPAR-γ, Smad2/3, and TAP63.

Quantitative single cell analysis of cell population dynamics during submandibular salivary gland development and differentiation

Epithelial organ morphogenesis involves reciprocal interactions between epithelial and mesenchymal cell types to balance progenitor cell retention and expansion with cell differentiation for evolution of tissue architecture. Underlying submandibular salivary gland branching morphogenesis is the regulated proliferation and differentiation of perhaps several progenitor cell populations, which have not been characterized throughout development, and yet are critical for understanding organ development, regeneration, and disease. Here we applied a serial multiplexed fluorescent immunohistochemistry technology to map the progressive refinement of the epithelial and mesenchymal cell populations throughout development from embryonic day 14 through postnatal day 20. Using computational single cell analysis methods, we simultaneously mapped the evolving temporal and spatial location of epithelial cells expressing subsets of differentiation and progenitor markers throughout salivary gland development. We mapped epithelial cell differentiation markers, including aquaporin 5, PSP, SABPA, and mucin 10 (acinar cells); cytokeratin 7 (ductal cells); and smooth muscle α-actin (myoepithelial cells) and epithelial progenitor cell markers, cytokeratin 5 and c-kit. We used pairwise correlation and visual mapping of the cells in multiplexed images to quantify the number of single- and double-positive cells expressing these differentiation and progenitor markers at each developmental stage. We identified smooth muscle α-actin as a putative early myoepithelial progenitor marker that is expressed in cytokeratin 5-negative cells. Additionally, our results reveal dynamic expansion and redistributions of c-kit- and K5-positive progenitor cell populations throughout development and in postnatal glands. The data suggest that there are temporally and spatially discreet progenitor populations that contribute to salivary gland development and homeostasis.

Arsenic suppresses cell survival via Pirh2-mediated proteasomal degradation of ΔNp63 protein

Transcription factor p63, a member of the p53 family, shares a high degree of sequence similarity with p53. Because of transcription from two distinct promoters, the p63 gene encodes two isoforms, TAp63 and ΔNp63. Although TAp63 acts as a tumor suppressor, ΔNp63 functions as an oncogene and is often overexpressed in squamous cell carcinomas. Thus, therapeutic agents targeting ΔNp63 might be used to manage tumors that overexpress ΔNp63. Here we found that arsenic trioxide, a frontline agent for acute promyelocytic leukemia, inhibits ΔNp63 but not TAp63 expression in time- and dose-dependent manners. In addition, we found that arsenic trioxide decreases the stability of ΔNp63 protein via a proteasome-dependent pathway but has little effect on the level of ΔNp63 transcript. Furthermore, we found that arsenic trioxide activates the Pirh2 promoter and consequently induces Pirh2 expression. Consistent with this, we found that knockdown of Pirh2 inhibits, whereas ectopic expression of Pirh2 enhances, arsenic-induced degradation of ΔNp63 protein. Importantly, we found that knockdown of ΔNp63 sensitizes, whereas ectopic expression of ΔNp63 inhibits, growth suppression induced by arsenic. Together, these data suggest that arsenic degrades ΔNp63 protein at least in part via Pirh2-dependent proteolysis and that inhibition of ΔNp63 expression facilitates tumor cells to arsenic-induced death.