Overexpression of the pituitary tumor transforming gene upregulates metastasis in malignant neoplasms of the human salivary glands

PTTG1: a Unique Regulator of Stem/Cancer Stem Cells in the Ovary and Ovarian Cancer

Origin of cancer stem cells (CSCs) and mechanisms by which oncogene PTTG1 contributes to tumor progression via CSCs is not known. Ovarian CSCs exhibit characteristics of self-renewal, tumor-initiation, growth, differentiation, drug resistance, and tumor relapse. A common location of putative origin, namely the ovarian surface epithelium, is shared between the normal stem and CSC compartments. Existence of ovarian stem cells and their co-expression with CSC signatures suggests a strong correlation between origin of epithelial cancer and CSCs. We hereby explored a putative oncogene PTTG1 (Securin), reported to be overexpressed in various tumors, including ovarian. We report a previously overlooked role of PTTG1 as a marker of CSCs thereby modulating CSC, germline, and stemness-related genes. We further characterized PTTG1's ability to regulate (cancer) stem cell-associated self-renewal and epithelial-mesenchymal transition pathways. Collectively, the data sheds light on a potential target expressed during ovarian tumorigenesis and metastatically disseminated ascites CSCs in the peritoneal cavity. Present study highlights this unconventional, under-explored role of PTTG1 in regulation of stem and CSC compartments in ovary, ovarian cancer and ascites and highlights it as a potential candidate for developing CSC specific targeted therapeutics.

Protein stabilization by RSUME accounts for PTTG pituitary tumor abundance and oncogenicity

Increased levels of the proto-oncogene pituitary tumor-transforming gene 1 (PTTG) have been repeatedly reported in several human solid tumors, especially in endocrine-related tumors such as pituitary adenomas. Securin PTTG has a critical role in pituitary tumorigenesis. However, the cause of upregulation has not been found yet, despite analyses made at the gene, promoter and mRNA level that show that no mutations, epigenetic modifications or other mechanisms that deregulate its expression may explain its overexpression and action as an oncogene. We describe that high PTTG protein levels are induced by the RWD-containing sumoylation enhancer (RWDD3 or RSUME), a protein originally identified in the same pituitary tumor cell line in which PTTG was also cloned. We demonstrate that PTTG and RSUME have a positive expression correlation in human pituitary adenomas. RSUME increases PTTG protein in pituitary tumor cell lines, prolongs the half-life of PTTG protein and regulates the PTTG induction by estradiol. As a consequence, RSUME enhances PTTG transcription factor and securin activities. PTTG hyperactivity on the cell cycle resulted in recurrent and unequal divisions without cytokinesis, and the consequential appearance of aneuploidies and multinucleated cells in the tumor. RSUME knockdown diminishes securin PTTG and reduces its tumorigenic potential in a xenograft mouse model. Taken together, our findings show that PTTG high protein steady state levels account for PTTG tumor abundance and demonstrate a critical role of RSUME in this process in pituitary tumor cells.

Integrated In Silico-In Vitro Identification and Characterization of the SH3-Mediated Interaction between Human PTTG and its Cognate Partners in Medulloblastoma

The human pituitary tumor-transforming gene is an oncogenic protein which serves as a central hub in the cellular signaling network of medulloblastoma. The protein contains two vicinal PxxP motifs at its C terminus that are potential binding sites of peptide-recognition SH3 domains. Here, a synthetic protocol that integrated in silico analysis and in vitro assay was described to identify the SH3-binding partners of pituitary tumor-transforming gene in the gene expression profile of medulloblastoma. In the procedure, a variety of structurally diverse, non-redundant SH3 domains with high gene expression in medulloblastoma were compiled, and their three-dimensional structures were either manually retrieved from the protein data bank database or computationally modeled through bioinformatics technique. The binding capability of these domains towards the two PxxP-containing peptides m1p: ¹⁶¹LGPPSPVK¹⁶⁸ and m2p: ¹⁶⁸KMPSPPWE¹⁷⁵ of pituitary tumor-transforming gene were ranked by structure-based scoring and fluorescence-based assay. Consequently, a number of SH3 domains, including MAP3K and PI3K, were found to have moderate or high affinity for m1p and/or m2p. Interestingly, the two overlapping peptides exhibits a distinct binding profile to these identified domain partners, suggesting that the binding selectivity of m1p and m2p is optimized across the medulloblastoma expression spectrum by competing for domain candidates. In addition, two redesigned versions of m1p peptide ware obtained via a structure-based rational mutation approach, which exhibited an increased affinity for the domain as compared to native peptide.

WISP-1 overexpression upregulates cell proliferation in human salivary gland carcinomas via regulating MMP-2 expression

BACKGROUND

WISP-1 is a member of the CCN family of growth factors and has been reported to play an important role in tumorigenesis by triggering downstream events via integrin signaling. However, little is known about the role of WISP-1 in proliferation of salivary gland carcinoma (SGC) cells.

METHODS

In this study, we investigated the WISP-1 expression in SGC tissues via immunohistochemical staining, Western blotting assay, and real-time quantitative polymerase chain reaction method, and then evaluated the regulatory role of WISP-1 in the growth of SGC A-253 cells. In addition, the role of MMP-2 in the WISP-1-mediated growth regulation was also investigated.

RESULTS

It was demonstrated that the WISP-1 expression was upregulated at both mRNA and protein levels in 15 of 21 SGC tumor tissues, compared to the non-tumor tissues (five of 21), associated with the lymph node dissection and bone invasion. The in vitro CCK-8 assay and colony-forming assay demonstrated that the exogenous WISP-1 treatment or the WISP-1 overexpression promoted the growth of A-253 cells. In addition, we confirmed that the WISP-1 overexpression upregulated the MMP-2 expression in A-253 cells with the gain-of-function and loss-of-function strategies, and that the MMP-2 knockdown attenuated the WISP-1-mediated growth promotion of A-253 cells.

CONCLUSION

We found that WISP-1 was overexpressed in the human SGCs, and the WISP-1 overexpression promoted the salivary gland cell proliferation via upregulating MMP-2 expression. Our study recognized the oncogenic role of WISP-1 in human SGCs, which could serve as a potential target for anticancer therapy.