Pro-invasive Effect of Proto-oncogene PBF Is Modulated by an Interaction with Cortactin

PTTG1IP (PBF) is a prognostic marker and correlates with immune infiltrate in ovarian cancer

OBJECTIVE

An oncogenic protein, pituitary tumor transforming gene 1 binding factor (PTTG1IP, also called PBF), has been found to be expressed in various cancers. However, few studies have explored its prognostic significance and biologic function in epithelial ovarian cancer (EOC).

METHODS

Based on the Cancer Genome Atlas (TCGA) database, this study determined the differential expression of PBF at the mRNA level in EOC and normal tissues, which was then verified using real-time PCR and western blotting. Moreover, the Kaplan-Meier method and the Cox regression method were adopted to assess the clinical value of PBF in EOC. A nomogram model was constructed to evaluate the prognostic performance of PBF in EOC. Gene set enrichment analysis (GSEA) was employed to evaluate the signaling and pathway enrichment of PBF in EOC. The association between PBF expression and tumor-infiltrating immune cells (TIICs) in EOC was examined by single-sample GSEA and TIMER.

RESULTS

PBF was significantly higher in EOC than normal tissues as shown through TCGA database, and this result was verified by qRT-PCR and western blotting of EOC tissues and different cell lines. High PBF was associated with tumor size and lymphatic metastasis status. Kaplan-Meier (KM) analysis indicated that high PBF expression correlated with poor prognosis in patients with EOC (P < 0.0001). Moreover, multivariate Cox regression analysis was used to verify that PBF is an independent prognostic factor for EOC. The nomogram model exhibited moderate predictive accuracy and clinical utility in predicting EOC prognosis. The GSEA revealed that the expression of signaling pathways, such DNA damage replication, p53 pathway, Akt phosphorylation pathway, and estrogen-dependent nuclear pathway, were increased in the phenotype with high PBF expression. PBF expression was associated with neutrophil cells, iDC cells, NK cells, and Tem cells.

CONCLUSION

As a prognostic biomarker for EOC, PBF was found to be correlated with immune infiltration, and may therefore be a promising target for immunotherapy for EOC.

Short-hairpin RNA-mediated suppression of cortactin may inhibit the migration and invasion abilities of endometrial cancer cells by reducing lamellipodia

Objectives

The prognosis of endometrial cancer (EC) is significantly affected by tumor infiltration and metastasis. Cortactin (CTTN) regulates infiltration and metastasis in other tumors. Studies on the role and mechanism of CTTN in EC are limited and further studies are needed.

Materials and Methods

Quantitative PCR and immunohistochemistry were used to detect Ras-associated C3 botulinum toxin substrate 1 (Rac1) and CTTN in EC and normal tissues. The relationship between the expression of these two genes and their prognostic factors was analyzed. A CTTN-RNAi lentiviral system was constructed and transfected into EC cells. Migration and invasion were evaluated by scratch assay, transwell migration, and invasion assays. Pseudopodia formation was observed by immunofluorescence staining. Western blotting was performed to detect the expression of Rac1.

Results

The expression levels of Rac1 and CTTN in EC tissues were significantly higher than those in normal tissues. In the EC group, Rac1 and CTTN levels were correlated. The protein expression levels of Rac1 and CTTN were related to myometrial invasion and stage. After CTTN knockdown, the migration rate, invasiveness, and migratory ability of EC cells decreased significantly. Lamellipodia was observed to disappear with the appearance of blebs. Rac1 protein expression was decreased after CTTN knockdown.

Conclusion

CTTN may promote the invasion and migration of EC by lamellipodia. This effect may be related to the regulation of Rac1 by CTTN.

Inhibition of clathrin-mediated endocytosis by knockdown of AP-2 leads to alterations in the plasma membrane proteome

In eukaryotic cells, clathrin-mediated endocytosis (CME) is a central pathway for the internalization of proteins from the cell surface, thereby contributing to the maintenance of the plasma membrane protein composition. A key component for the formation of endocytic clathrin-coated vesicles (CCVs) is AP-2, as it sequesters cargo membrane proteins, recruits a multitude of other endocytic factors and initiates clathrin polymerization. Here, we inhibited CME by depletion of AP-2 and explored the consequences for the plasma membrane proteome. Quantitative analysis revealed accumulation of major constituents of the endosomal-lysosomal system reflecting a block in retrieval by compensatory CME. The noticeable enrichment of integrins and blockage of their turnover resulted in severely impaired cell migration. Rare proteins such as the anti-cancer drug target CA9 and tumor markers (CD73, CD164, CD302) were significantly enriched. The AP-2 knockdown attenuated the global endocytic capacity, but clathrin-independent entry pathways were still operating, as indicated by persistent internalization of specific membrane-spanning and GPI-anchored receptors (PVR, IGF1R, CD55, TNAP). We hypothesize that blocking AP-2 function and thus inhibiting CME may be a novel approach to identify new druggable targets, or to increase their residence time at the plasma membrane, thereby increasing the probability for efficient therapeutic intervention.

SLC34A2 simultaneously promotes papillary thyroid carcinoma growth and invasion through distinct mechanisms

Thyroid cancer is the fastest growing cancer among all solid tumors in recent decades. Papillary thyroid carcinoma (PTC) is the most predominant type of thyroid cancer. Around 30% of PTC patients with distant metastases and local invasion receive poor prognosis. Thus, the identification of new druggable biological targets is of great importance. Accumulating evidence indicates that solute carrier family numbers have emerged as obligate effectors during the progression of multiple malignancies. Here, we uncovered the functional significance, molecular mechanisms, and clinical impact of solute carrier family 34 member A2 (SLC34A2) in PTC. SLC34A2 was markedly overexpressed in PTC tissues at both mRNA and protein levels compared with matched adjacent normal tissues due to promoter hypomethylation mediated by the DNA methyltransferase 3 beta (DNMT3B). Furthermore, a series of in vivo and in vitro gain- or loss-of-functional assays elucidated the role of SLC34A2 in boosting cell proliferation, cell cycle progression, migration, invasion, and adhesion of PTC cells. Using immunoprecipitation and mass spectrometry, we discovered that SLC34A2 bound to the actin-binding repeats domain of Cortactin (CTTN), thereby inducing the invadopodia formation of PTC cells to promote the metastasis potential of PTC cells. Besides, our mechanistic studies, as well as gene set enrichment analysis (GSEA), have pinpointed the PTEN/AKT/FOXO3a pathway as a major signaling functioning downstream of SLC34A2 regulated cell growth. Taken together, our results highlighted that SLC34A2 plays a pivotal oncogenic role during carcinogenesis and metastasis through distinct mechanisms in PTC.

PBF, a Proto-oncogene in Esophageal Carcinoma

Emerging evidence shows that the pituitary tumour-transforming gene (PTTG)-binding factor (PBF) functions as a proto-oncogene in some tumors. However, the precise functions of PBF in tumorigenesis and its action mechanisms remain largely unknown. Here for the first time we demonstrated that PBF was associated with a tumor-related cell phenotype in esophageal carcinoma (ESCA) and identified the involved signaling pathways. PBF was up-regulated in ESCA tissues (Data from GEPIA) and cells. Then we down-regulated PBF in ESCA cell lines, Eca-109 and TE-1, by using RNAi technology. Cell function analysis suggested that down-regulation of PBF could inhibit tumor-related cell phenotypes, including proliferation, motility, apoptosis and cell cycle, in Eca-109 and TE-1 cells. Mechanism investigation suggested that apoptosis induced by PBF knockdown may be mediated by the activation of the mitochondrial apoptosis pathway and cell cycle arrest. AKT/mTOR and Wnt3a/β-catenin, key pathways in regulating tumor proliferation and metastasis, were found to be inactivated by the down-regulation of PBF in ESCA cells. In conclusion, our study demonstrates that PBF functions as a proto-oncogene in ESCA in vitro, which may be mediated through AKT/mTOR and Wnt3a/β-catenin pathways.

PTTG and PBF Functionally Interact with p53 and Predict Overall Survival in Head and Neck Cancer

Head and neck squamous cell carcinoma (HNSCC) is the 6th most common cancer worldwide and poses a significant health burden due to its rising incidence. Although the proto-oncogene pituitary tumor-transforming gene 1 (PTTG) predicts poor patient outcome, its mechanisms of action are incompletely understood. We show here that the protein PBF modulates PTTG function, is overexpressed in HNSCC tumors, and correlates with significantly reduced survival. Lentiviral shRNA attenuation of PTTG or PBF expression in HNSCC cells with either wild-type or mutant p53, and with and without HPV infection, led to dysregulated expression of p53 target genes involved in DNA repair and apoptosis. Mechanistically, PTTG and PBF affected each other's interaction with p53 and cooperated to reduce p53 protein stability in HNSCC cells independently of HPV. Depletion of either PTTG or PBF significantly repressed cellular migration and invasion and impaired colony formation in HNSCC cells, implicating both proto-oncogenes in basic mechanisms of tumorigenesis. Patients with HNSCC with high tumoral PBF and PTTG had the poorest overall survival, which reflects a marked impairment of p53-dependent signaling.Significance: These findings reveal a complex and novel interrelationship between the expression and function of PTTG, PBF, and p53 in human HNSCC that significantly influences patient outcome. Cancer Res; 78(20); 5863-76. ©2018 AACR.

Cortactin function in invadopodia

Actin remodeling plays an essential role in diverse cellular processes such as cell motility, vesicle trafficking or cytokinesis. The scaffold protein and actin nucleation promoting factor Cortactin is present in virtually all actin-based structures, participating in the formation of branched actin networks. It has been involved in the control of endocytosis, and vesicle trafficking, axon guidance and organization, as well as adhesion, migration and invasion. To migrate and invade through three-dimensional environments, cells have developed specialized actin-based structures called invadosomes, a generic term to designate invadopodia and podosomes. Cortactin has emerged as a critical regulator of invadosome formation, function and disassembly. Underscoring this role, Cortactin is frequently overexpressed in several types of invasive cancers. Herein we will review the roles played by Cortactin in these specific invasive structures.

Functional consequences of the first reported mutations of the proto-oncogene PTTG1IP/PBF

Pituitary tumor-transforming gene 1-binding factor (PTTG1IP; PBF) is a multifunctional glycoprotein, which is overexpressed in a wide range of tumours, and significantly associated with poorer oncological outcomes, such as early tumour recurrence, distant metastasis, extramural vascular invasion and decreased disease-specific survival. PBF transforms NIH 3T3 fibroblasts and induces tumours in nude mice, while mice harbouring transgenic thyroidal PBF expression show hyperplasia and macrofollicular lesions. Our assumption that PBF becomes an oncogene purely through increased expression has been challenged by the recent report of mutations in PBF within the Catalogue of Somatic Mutations in Cancer (COSMIC) database. We therefore sought to determine whether the first 10 PBF missense substitutions in human cancer might be oncogenic. Anisomycin half-life studies revealed that most mutations were associated with reduced protein stability compared to wild-type (WT) PBF. Proliferation assays narrowed our interest to two mutational events which significantly altered cell turnover: C51R and R140W. C51R was mainly confined to the endoplasmic reticulum while R140W was apparent in the Golgi apparatus. Both C51R and R140W lost the capacity to induce cellular migration and significantly reduced cell invasion. Colony formation and soft agar assays demonstrated that, in contrast to WT PBF, both mutants were unable to elicit significant colony formation or anchorage-independent growth. However, C51R and R140W retained the ability to repress radioiodide uptake, a functional hallmark of PBF. Our data reveal new insight into PBF function and confirm that, rather than being oncogenic, mutations in PBF are likely to be passenger effects, with overexpression of PBF the more important aetiological event in human cancer.