The clinicopathological significances and biological functions of parafibromin expression in head and neck squamous cell carcinomas

Parafibromin governs cell polarity and centrosome assembly in Drosophila neural stem cells

Neural stem cells (NSCs) divide asymmetrically to balance their self-renewal and differentiation, an imbalance in which can lead to NSC overgrowth and tumor formation. The functions of Parafibromin, a conserved tumor suppressor, in the nervous system are not established. Here, we demonstrate that Drosophila Parafibromin/Hyrax (Hyx) inhibits ectopic NSC formation by governing cell polarity. Hyx is essential for the asymmetric distribution and/or maintenance of polarity proteins. hyx depletion results in the symmetric division of NSCs, leading to the formation of supernumerary NSCs in the larval brain. Importantly, we show that human Parafibromin rescues the ectopic NSC phenotype in Drosophila hyx mutant brains. We have also discovered that Hyx is required for the proper formation of interphase microtubule-organizing center and mitotic spindles in NSCs. Moreover, Hyx is required for the proper localization of 2 key centrosomal proteins, Polo and AurA, and the microtubule-binding proteins Msps and D-TACC in dividing NSCs. Furthermore, Hyx directly regulates the polo and aurA expression in vitro. Finally, overexpression of polo and aurA could significantly suppress ectopic NSC formation and NSC polarity defects caused by hyx depletion. Our data support a model in which Hyx promotes the expression of polo and aurA in NSCs and, in turn, regulates cell polarity and centrosome/microtubule assembly. This new paradigm may be relevant to future studies on Parafibromin/HRPT2-associated cancers.

This study shows that the conserved tumor suppressor Parafibromin plays an important role in Drosophila neural stem cell function, regulating the expression of the centrosomal proteins Polo and AurA, modulating centrosome and microtubule assembly, and ultimately influencing neural stem cell polarity during cell division.

The roles of the tumor suppressor parafibromin in cancer

In this review, we discuss parafibromin protein, which is encoded by CDC73. A mutation in this gene causes hyperparathyroidism-jaw tumor (HPT-JT) syndrome, an autosomal dominant disease. CDC73 is transcriptionally downregulated by the Wilms’ tumor suppressor gene WT1 and translationally targeted by miR-182-3p and miR-155. In the nucleus, parafibromin binds to RNA polymerase II and PAF1 complex for transcription. Parafibromin transcriptionally increases the expression of c-Myc, decreases CPEB1 expression by interacting with H3M4, and reduces cyclin D1 expression by binding to H3K9. The RNF20/RNF40/parafibromin complex induces monoubiquitination of H2B-K120, and SHP2-mediated dephosphorylation of parafibromin promotes the parafibromin/β-catenin interaction and induces the expression of Wnt target genes, which is blocked by PTK6-medidated phosphorylation. Parafibromin physically associates with the CPSF and CstF complexes that are essential for INTS6 mRNA maturation. In the cytosol, parafibromin binds to hSki8 and eEF1Bγ for the destabilization of p53 mRNA, to JAK1/2-STAT1 for STAT1 phosphorylation, and to actinin-2/3 to bundle/cross-link actin filaments. Mice with CDC73 knockout in the parathyroid develop parathyroid and uterine tumors and are used as a model for HPT-JT syndrome. Conditional deletion of CDC73 in mesenchymal progenitors results in embryos with agenesis of the heart and liver while its abrogation in mature osteoblasts and osteocytes increases cortical and trabecular bone. Heterozygous germline mutations in CDC73 are associated with parathyroid carcinogenesis. The rates of CDC73 mutation and parafibromin loss decrease from parathyroid adenoma to atypical adenoma to carcinoma. In addition, down-regulated parafibromin is closely linked to the tumorigenesis, subsequent progression, or poor prognosis of head and neck, gastric, lung, colorectal, and ovarian cancers, and its overexpression might reverse the aggressiveness of these cancer cells. Therefore, parafibromin might be useful as a biological marker of malignancies and a target for their gene therapy.

Identification of Common Driver Gene Modules and Associations between Cancers through Integrated Network Analysis

High-throughput biological data has created an unprecedented opportunity for illuminating the mechanisms of tumor emergence and evolution. An important and challenging problem in deciphering cancers is to investigate the commonalities of driver genes and pathways and the associations between cancers. Aiming at this problem, a tool ComCovEx is developed to identify common cancer driver gene modules between two cancers by searching for the candidates in local signaling networks using an exclusivity-coverage iteration strategy and outputting those with significant coverage and exclusivity for both cancers. The associations of the cancer pairs are further evaluated by Fisher's exact test. Being applied to 11 TCGA cancer datasets, ComCovEx identifies 13 significantly associated cancer pairs with plenty of biologically significant common gene modules. The novel results of cancer relationship and common gene modules reveal the relevant pathological basis of different cancer types and provide new clues to diagnosis and drug treatment in associated cancers.

MAPK/FoxA2-mediated cigarette smoke-induced squamous metaplasia of bronchial epithelial cells

Objective

To explore the effect of cigarette smoke (CS) on the development of squamous metaplasia in human airway epithelial cells and the role of MAPK- and FoxA2-signaling pathways in the process.

Materials and methods

In an in vitro study, we treated the bronchial epithelial cell line BEAS2B with CS extract, followed by treatment with the ERK inhibitor U0126, the JNK inhibitor SP600125, or the p38 inhibitor SB203580. In vivo, we used a CS-induced rat model. After treatment with CS with or without MAPK inhibitors for 90 days, lung tissues were harvested. p-ERK, p-p38 and p-JNK protein levels in cells and lung tissue were measured using enzyme-linked immunosorbent assays, mRNA- and protein-expression profiles of FoxA2, E-cadherin, CD44, and ZO1 were measured using quantitative real-time polymerase chain reaction and Western blotting, respectively, and morphological changes in bronchial epithelial cells were observed using lung-tissue staining.

Results

In both the in vitro and in vivo studies, phosphorylation of the ERK1/2, JNK, and p38 proteins was significantly increased (P<0.05) and mRNA and protein expression of E-cadherin and FoxA2 significantly decreased (P<0.05) compared with the control group. ERK, JNK, and p38 inhibitors reversed the CS-extract-induced changes in E-cadherin, CD44, and ZO1 mRNA and protein expression (P<0.05), decreased p-ERK, p-p38, and p-JNK protein levels in cells and lung tissue, suppressed bronchial epithelial hyperplasia and local squamous metaplasia, and decreased FoxA2 expression.

Conclusion

MAPK and FoxA2 mediate CS-induced squamous metaplasia. MAPK inhibitors upregulate FoxA2, resulting in a reduction in the degree of squamous metaplasia.

The clinicopathological and prognostic significances of CDC73 expression in cancers: a bioinformatics analysis

CDC73 interacts with human PAF1 complex, histone methyltransferase complex and RNA polymerase II for transcription elongation and 3’ end processing. Its down-regulated expression was immunohistochemically detected in gastric, colorectal, ovarian and head and neck cancers, and positively correlated with aggressive behaviors and unfavorable prognosis of malignancies. We performed a bioinformatics analysis by using Oncomine, TCGA and KM plotter databases. It was found that CDC73 mRNA was overexpressed in gastric, lung, breast and ovarian cancers, even stratified by histological subtypes (p<0.05). CDC73 mRNA expression was stronger in gastric intestinal- than diffuse-type carcinomas (p<0.05), and positively correlated with distant metastasis and TNM staging of lung cancer (p<0.05). CDC73 mRNA expression was positively related to both overall and progression-free survival rates of the patients with gastric cancer, even stratified by gender, lymph node involvement, or treatment (p<0.05), while versa for breast cancer (p<0.05). The prognostic significance of CDC73 mRNA was dependent on the datasets and pathological grouping in lung and ovarian cancers. These findings indicated the CDC73 mRNA overexpression was positively linked to carcinogenesis. It is cautious to employ CDC73 mRNA to evaluate the clinicopathological behaviors and prognosis of cancers.

The in vitro and vivo effects of nuclear and cytosolic parafibromin expression on the aggressive phenotypes of colorectal cancer cells: a search of potential gene therapy target

Down-regulated parafibromin is positively linked to the pathogenesis of parathyroid, lung, breast, ovarian, gastric and colorectal cancers. Here, we found that wild-type (WT) parafibromin overexpression suppressed proliferation, tumor growth, induced cell cycle arrest and apoptosis in colorectal cancer cells (p<0.05), but it was the converse for mutant-type (MT, mutation in nucleus localization sequence) parafibromin (p<0.05). Both WT and MT transfectants inhibited migration and invasion, and caused better differentiation (p<0.05) of cancer cells. WT parafibromin transfectants showed the overexpression of Cyclin B1, Cyclin D1, Cyclin E, p38, p53, and AIF in HCT-15 and HCT-116 cells, while MT parafibromin only up-regulated p38 expression. There was lower mRNA expression of bcl-2 in parafibromin transfectants than the control and mock, while higher expression of c-myc, Cyclin D1, mTOR, and Raptor. According to transcriptomic analysis, WT parafibromin suppressed PI3K-Akt and FoxO signaling pathways, while MT one promoted PI3K-Akt pathway, focal adhesion, and regulation of actin cytoskeleton. Parafibromin was less expressed in colorectal cancer than paired mucosa (p<0.05), and inversely correlated with its differentiation at both mRNA and protein levels (p<0.05). These findings indicated that WT parafibromin might reverse the aggressive phenotypes of colorectal cancer cells and be employed as a target for gene therapy. Down-regulated parafibromin expression might be closely linked to colorectal carcinogenesis and cancer differentiation.

Significance of Parafibromin Expression in Laryngeal Squamous Cell Carcinomas

BACKGROUND

Parafibromin is a product of the tumor suppressor gene that has been studied as a potential indicator of tumor aggressiveness in the parathyroid, breast, colorectum, and stomach. However, the clinical significance and potential function of parafibromin expression in head and neck squamous cell carcinomas remain largely unknown. The aim of this study was to evaluate the expression of parafibromin in laryngeal squamous cell carcinoma (LSCC) and to verify its potential as a biomarker of tumor behavior.

METHODS

Parafibromin expression was evaluated in 30 cases of LSCC using immunohistochemistry. The correlations between parafibromin expression and clinicopathologic parameters were investigated.

RESULTS

Parafibromin expression was positive in 15 cases (50%) and negative in 15 cases (50%). Tumor size and T stage showed a statistically significant inverse relationship with parafibromin expression (p=.028 and p<.001, respectively). Parafibromin expression was not associated with age, sex, lymph node metastasis, tumor differentiation, or tumor location. There was no statistically significant relationship between parafibromin expression and progression-free survival in the patients (p>.05).

CONCLUSIONS

Our results indicate that the downregulation or loss of parafibromin expression can be employed as a novel marker of tumor progression or aggressiveness in LSCC.

The roles of parafibromin expression in ovarian epithelial carcinomas: a marker for differentiation and prognosis and a target for gene therapy

Parafibromin is a protein encoded by hyperparathyroidism 2 (HRPT2) and its downregulated expression is involved in the pathogenesis of parathyroid, breast, gastric, colorectal, lung, head and neck cancers. We aimed to investigate the roles of parafibromin expression in tumorigenesis, progression, or prognostic evaluation of ovarian cancers. HRPT2-expressing plasmid was transfected into ovarian cancer cells with the phenotypes and related molecules examined. The messenger RNA (mRNA) and protein expression of parafibromin were also examined in ovarian normal tissue, benign and borderline tumors and cancers by reverse transcription-polymerase chain reaction (RT-PCR), Western blot, or immunohistochemistry respectively. It was found that parafibromin overexpression caused a lower growth, migration and invasion, higher sensitivity to cisplatin and apoptosis than the mock and control (P < 0.05). The transfectants showed the hypoexpression of phosphoinositide 3-kinase (PI3K), Akt, p70 ribosomal protein S6 kinase (p70s6k), Wnt5a, B cell lymphoma-extra large (Bcl-xL), survivin, vascular endothelial growth factor (VEGF) and matrix metallopeptidase 9 (MMP-9) than the mock and control at both mRNA and protein levels (P < 0.05). According to real-time PCR, parafibromin mRNA level was lower in ovarian benign tumors and cancers than normal ovary (P < 0.05), while parafibromin was strongly expressed in metastatic cancers in omentum than primary cancers by Western blot. Immunohistochemically, parafibromin expression was stronger in primary cancers than that in ovarian normal tissue (P < 0.05) but weaker than the metastatic cancers (P < 0.05) with a positive correlation with dedifferentiation, ki-67 expression and the lower cumulative survival rate (P < 0.05). These findings indicate that parafibromin downregulation might promote the pathogenesis, dedifferentiation and metastasis of ovarian cancers possibly by suppressing aggressive phenotypes, such as proliferation, cell cycle, apoptosis, migration and invasion.