Centrosomal dysregulation in human metastatic melanoma cell lines

Genetic and Genomic Pathways of Melanoma Development, Invasion and Metastasis

Melanoma is a serious form of skin cancer that accounts for 80% of skin cancer deaths. Recent studies have suggested that melanoma invasiveness is attributed to phenotype switching, which is a reversible type of cell behaviour with similarities to epithelial to mesenchymal transition. Phenotype switching in melanoma is reported to be independent of genetic alterations, whereas changes in gene transcription, and epigenetic alterations have been associated with invasiveness in melanoma cell lines. Here, we review mutational, transcriptional, and epigenomic alterations that contribute to tumour heterogeneity in melanoma, and their potential to drive melanoma invasion and metastasis. We also discuss three models that are hypothesized to contribute towards aspects of tumour heterogeneity and tumour progression in melanoma, namely the clonal evolution model, the cancer stem cell model, and the phenotype switching model. We discuss the merits and disadvantages of each model in explaining tumour heterogeneity in melanoma, as a precursor to invasion and metastasis.

Increased SPC24 in prostatic diseases and diagnostic value of SPC24 and its interacting partners in prostate cancer

SPC24 is a crucial component of the mitotic checkpoint machinery in tumorigenesis. High levels of SPC24 have been found in various cancers, including breast cancer, lung cancer, liver cancer, osteosarcoma and thyroid cancer. However, to the best of our knowledge, the impact of SPC24 on prostate cancer (PCa) and other prostate diseases remains unclear. In the present study expression of global SPC24 messenger RNA (mRNA) was assessed in a subset of patients with PCa included in The Cancer Genome Atlas (TCGA) database. Increased levels of SPC24 expression were found in PCa patients >60 years old compared to patients <60 and increased SPC24 expression was also associated with higher levels of prostate specific antigen (P<0.05) and lymph node metastasis (P<0.05). Higher levels of SPC24 expression were associated with negative outcomes in PCa patients (P<0.05). Furthermore, in Chinese patients with prostatitis, benign prostatic hypertrophy (BPH) and PCa, SPC24 was expressed at significantly higher levels than that in adjacent/normal tissues, as assessed by reverse transcription-quantitative polymerase chain reaction, immunohistochemistry and western blotting. High expression of SPC24 was associated with high Gleason stages (IV and V; P<0.05). Further analysis, based on Gene Ontology and pathway functional enrichment analysis, suggested that nuclear division cycle 80 (NDC80), an SPC24 protein interaction partner, and mitotic spindle checkpoint serine/threonine-protein kinase BUB1 (BUB1), a core subunit of the spindle assembly checkpoint, may be associated with SPC24 in PCa development. Finally, using binary logistic regression, algorithms combining the receiver operating characteristic between SPC24 and BUB1 or NDC80 indicated that a combination of these markers may provide better PCa diagnosis ability than other PCa diagnosis markers. Taken together, these findings suggest that SPC24 may be a promising prostate disease biomarker.

Loss of Both CDKN2A and CDKN2B Allows for Centrosome Overduplication in Melanoma

Centrosomes duplicate only once in coordination with the DNA replication cycle and have an important role in segregating genetic material. In contrast, most cancer cells have centrosome aberrations, including supernumerary centrosomes, and this correlates with aneuploidy and genetic instability. The tumor suppressors p16 (CDKN2A) and p15 (CDKN2B) (encoded by the familial melanoma CDKN2 locus) inhibit CDK4/6 activity and have important roles in cellular senescence. p16 is also associated with suppressing centrosomal aberrations in breast cancer; however, the role of p15 in centrosome amplification is unknown. Here, we investigated the relationship between p15 and p16 expression, centrosome number abnormalities, and melanoma progression in cell lines derived from various stages of melanoma progression. We found that normal human melanocyte lines did not exhibit centrosome number abnormalities, whereas those from later stages of melanoma did. Additionally, under conditions of S-phase block, p15 and p16 status determined whether centrosome overduplication would occur. Indeed, removal of p15 from p16-negative cell lines derived from various stages of melanoma progression changed cells that previously would not overduplicate their centrosomes into cells that did. Although this study used cell lines in vitro, it suggests that, during clinical melanoma progression, sequential loss of p15 and p16 provides conditions for centrosome duplication to become deregulated with consequences for genome instability.

Centriole Overduplication is the Predominant Mechanism Leading to Centrosome Amplification in Melanoma

Centrosome amplification (CA) is common in cancer and can arise by centriole overduplication or by cell doubling events, including the failure of cell division and cell-cell fusion. To assess the relative contributions of these two mechanisms, the number of centrosomes with mature/mother centrioles was examined by immunofluorescence in a tissue microarray of human melanomas and benign nevi (n = 79 and 17, respectively). The centrosomal protein 170 (CEP170) was used to identify centrosomes with mature centrioles; this is expected to be present in most centrosomes with cell doubling, but on fewer centrosomes with overduplication. Using this method, it was determined that the majority of CA in melanoma can be attributed to centriole overduplication rather than cell doubling events. As Polo-like kinase 4 (PLK4) is the master regulator of centriole duplication, the hypothesis that PLK4 overexpression contributes to centriole overduplication was evaluated. PLK4 is significantly overexpressed in melanoma compared with benign nevi and in a panel of human melanoma cell lines (A375, Hs294T, G361, WM35, WM115, 451Lu, and SK-MEL-28) compared with normal human melanocytes. Interestingly, although PLK4 expression did not correlate with CA in most cases, treatment of melanoma cells with a selective small-molecule PLK4 inhibitor (centrinone B) significantly decreased cell proliferation. The antiproliferative effects of centrinone B were also accompanied by induction of apoptosis.Implications: This study demonstrates that centriole overduplication is the predominant mechanism leading to centrosome amplification in melanoma and that PLK4 should be further evaluated as a potential therapeutic target for melanoma treatment. Mol Cancer Res; 16(3); 517-27. ©2018 AACR.

A novel prognostic biomarker SPC24 up-regulated in hepatocellular carcinoma

SPC24 is an important component of the nuclear division cycle 80 (Ndc80) kinetochore complex, which plays an essential role in the coupling of kinetochore to spindle microtubules (MTs) and the accurate segregation of chromosomes during mitosis. However, the functional role of SPC24 in hepatocellular carcinoma (HCC) remains unknown. Here, we detected the expression of SPC24 in HCC and analyzed its association with clinicopathologic features and prognosis of HCC patients. The expression of SPC24 mRNA was investigated in 212 cases of paired HCC and adjacent liver tissues by quantitative real-time PCR (qRT-PCR) and in the tissues of 20 HCC patients by semi-quantitative RT-PCR. Additionally, the expression of SPC24 protein was detected in 69 cases of HCC by immunohistochemistry (IHC) or in 2 cases of HCC tissues by Western-blotting. Furthermore, small interfering RNA (siRNA)-mediated silencing of SPC24 was employed in SMMC7721 and HepG2 human HCC cells to investigate cell proliferation, invasion and apoptosis. Survival curves were plotted using the Kaplan-Meier method, and differences in survival probability were obtained using the log-rank test. Independent predictors associated with disease-free survival (DFS) and overall survival (OS) were analyzed using the Cox proportional-hazards regression model. In this study, we showed that SPC24 was noticeably increased in HCC tissues compared to normal adjacent noncancerous tissues, at both mRNA and protein levels. High expression of SPC24 was significantly correlated with alpha-fetoprotein (AFP) (p = 0.044), median size (p = 0.030), tumor number (p = 0.019), and Barcelona-Clinic Liver Cancer (BCLC) stage (p = 0.015). Kaplan-Meier analysis showed that the DFS and OS of high SPC24 expression group was significantly shorter than that of low SPC24 expression group (p < 0.001; p = 0.001; respectively). The prognostic impact of SPC24 was further confirmed by stratified survival analysis. Importantly, multivariate analysis identified SPC24 upregualtion (p = 0.001), PVTT (p = 0.007), size of tumor > 5 cm (p < 0.001) as independent risk factors of DFS after resection, and SPC24 upregualtion (p < 0.001), PVTT (p = 0.029), size of tumor > 5 cm (p = 0.002), recurrence (p < 0.001) as independent prognostic factors for the OS of HCC patients. Additionally, siRNA-mediated silencing of SPC24 dramatically suppressed cell growth, adhesion, invasion and increased apoptosis in HCC cells. In conclusion, these results showed for the first time that SPC24 expression was significantly up-regulated in HCC, which may act as a novel prognostic biomarker for patients suffering from this deadly disease. Additionally, silence of SPC24 inhibiting HCC cell growth indicated that SPC24 may be a promising molecular target for HCC therapy.

siRNA-mediated knockdown against NUF2 suppresses pancreatic cancer proliferation in vitro and in vivo

NUF2 (NUF2, Ndc80 kinetochore complex component) plays an important role in kinetochore-microtubule attachment. It has been reported that NUF2 is associated with multiple human cancers. However, the functional role of NUF2 in pancreatic cancer remains unclear. In this study, we found that NUF2 expression was stronger in tumour tissues than in normal pancreatic tissues, and its overexpression could be related to poor prognosis. Moreover, NUF2 was highly expressed in several human pancreatic cancer cell lines. We took advantage of lentivirus-mediated siRNA (small interfering RNA) to suppress NUF2 expression in PANC-1 and Sw1990 cell lines aiming to investigate the role of NUF2 in pancreatic cancer. NUF2 silencing by RANi (RNA interference) reduced the proliferation and colony formation ability of pancreatic cancer cells in vitro. Cell cycle analysis showed that NUF2 knockdown induced cell cycle arrest at G0/G1 phase via suppression of Cyclin B1, Cdc2 and Cdc25A. More importantly, NUF2 silencing was able to alleviate in vivo tumourigenesis in pancreatic cancer xenograft nude mice. Collectively, the present study indicates that the siRNA-mediated knockdown against NUF2 may be a promising therapeutic method for the treatment of pancreatic cancer.

NUF2 is overexpressed in pancreatic cancer tissues and cell lines. siRNA-mediated knockdown against NUF2 resulted in a significant reduction in pancreatic cancer cell growth both in vitro and in vivo. NUF2 may be a promising therapeutic target in pancreatic cancer.

Heterogeneity of expression of epithelial-mesenchymal transition markers in melanocytes and melanoma cell lines

The epithelial–mesenchymal transition (EMT) describes a reversible switch from an epithelial-like to a mesenchymal-like phenotype. It is essential for the development of the normal epithelium and also contributes to the invasive properties of carcinomas. At the molecular level, the EMT transition is characterized by a series of coordinated changes including downregulation of the junctional protein E-cadherin (CDH1), up-regulation of transcriptional repressors of E-cadherin such as Snail (SNAI1) and Slug (SNAI2), and up-regulation of N-cadherin. We wished to determine whether cultured normal melanocytes and melanoma cell lines, which are derived from the neural crest, showed signs of a similarly coordinated phenotypic switch. We investigated normal melanocytes and 25 cell lines derived from New Zealand patients with metastatic melanoma. Most lines had been previously genotyped for common mutations such as BRAF, NRAS, PIK3CA (phosphatidylinositol-3-kinase), TP53 (p53), and CDKN2A (p16). Expression of E-cadherin, N-cadherin, microphthalmia-associated transcription factor (MITF), Snail, Slug, Axl, p53, and Hdm2 was compared by western blotting. Normal melanocytes expressed each of these proteins except for Snail, while normal melanocytes and almost every melanoma line expressed Slug. Expression of individual markers among different melanoma lines varied from high to low or undetectable. Quantitation of western blots showed that expression of MITF-M, the melanocyte-specific isoform of MITF, was positively related to that of E-cadherin but inversely related to that of N-cadherin and Axl. There was also no apparent relationship between expression of any particular marker and the presence of BRAF, NRAS, PIK3CA, TP53, or CDKN2A mutations. The results suggest that melanomas do not show the classical epithelial and mesenchymal phenotypes but rather display either high E-cadherin/high MITF-M expression on one hand, or high N-cadherin/high Axl expression on the other. These may correspond to differentiated and invasive phenotypes in vivo.

The role of the hippo pathway in melanocytes and melanoma

The Hippo signaling pathway comprises a series of cytoplasmic tumor suppressor proteins including Merlin and the Lats1/2 and MST1/2 kinases, and is thought to play a critical role in determining the sizes of organs and tissues. The Hippo pathway is regulated upstream by extracellular mechanosensory signaling arising from cell shape and polarity, as well as by a variety of extracellular signaling molecules. When active, the pathway maintains the transcriptional activators Yes-associated protein (YAP) and TAZ in phosphorylated forms in the cytoplasm, preventing cell proliferation. When the Hippo pathway is inactivated, YAP and TAZ are translocated to the nucleus and induce the expression of a variety of proteins concerned with entry into the cell division cycle, such as cyclin D1 and Fox M1, as well as the inhibition of apoptosis. The failure of the Hippo pathway has been implicated in the development of many different types of cancer but there is limited information available as to its involvement in melanoma. We hypothesize here firstly that the Hippo pathway is involved in maintaining density of cutaneous melanocytes on the basement membrane at the junction of the epidermis and the dermis, and secondly, that its function is disturbed in melanoma. We have analyzed a series of 23 low passage human melanoma lines as well as cultured normal melanoma, and find that melanocytes, as well as all melanoma cell lines examined express TAZ. Melanocytes and most melanoma lines also express YAP. E-cadherin, an upstream regulator of the Hippo pathway, and Axl, a receptor tyrosine kinase regulated by the Hippo pathway, are expressed in melanocytes and in several melanoma cell lines. These observations, together with published evidence for the presence of Merlin, Lats1/2, and MST1/2 in melanocytes and melanoma cells, support the hypothesis that the Hippo pathway is an important component of melanocyte and melanoma behavior.

Comparison of responses of human melanoma cell lines to MEK and BRAF inhibitors

The NRAS and BRAF genes are frequently mutated in melanoma, suggesting that the NRAS-BRAF-MEK-ERK signaling pathway is an important target for therapy. Two classes of drugs, one targeting activated BRAF and one targeting MEK, are currently undergoing clinical evaluation. We have analysed the NRAS and BRAF mutational status of a series of 44 early passage lines developed from New Zealand patients with metastatic melanoma. 41% of the lines analysed had BRAF mutations, 23% had NRAS mutations, and 36% had neither. We then determined IC₅₀ values (drug concentrations for 50% growth inhibition) for CI-1040, a commonly used inhibitor of MEK kinase; trametinib, a clinical agent targeting MEK kinase; and vemurafenib, an inhibitor of mutant BRAF kinase. Cell lines with activating BRAF mutations were significantly more sensitive to vemurafenib than lines with NRAS mutations or lines lacking either mutation (p < 0.001). IC₅₀ values for CI-1040 and trametinib were strongly correlated (r = 0.98) with trametinib showing ~100-fold greater potency. Cell lines sensitive to vemurafenib were also sensitive to CI-1040 and trametinib, but there was no relationship between IC₅₀ values and NRAS mutation status. A small number of lines lacking a BRAF mutation were sensitive to CI-1040 but resistant to vemurafenib. We used western blotting to investigate the effect on ERK phosphorylation of CI-1040 in four lines, of vemurafenib in two lines and of trametinib in two lines. The results support the view that MEK inhibitors might be combined with BRAF inhibitors in the treatment of melanomas with activated BRAF. The high sensitivity to trametinib of some lines with wildtype BRAF status also suggests that MEK inhibitors could have a therapeutic effect against some melanomas as single agents.

Pericentrin in health and disease: Exploring the patchwork of Pericentrin splice variants

Researchers around the world perform large-scale screens to identify disease-related gene defects in humans. One of the genes of interest is Pericentrin (PCNT), a gene which codes for a large coiled-coil protein with multiple functions in the cell. Recently, we showed that different Pericentrin (Pcnt) splice variants are differentially distributed among sensory tissues of the mouse, emphasizing the importance of a protein‘s spliceome for the function of a cell.

An RNA interference lethality screen of the human druggable genome to identify molecular vulnerabilities in epithelial ovarian cancer

Targeted therapies have been used to combat many tumor types; however, few have effectively improved the overall survival in women with epithelial ovarian cancer, begging for a better understanding of this deadly disease and identification of essential drivers of tumorigenesis that can be targeted effectively. Therefore, we used a loss-of-function screening approach to help identify molecular vulnerabilities that may represent key points of therapeutic intervention. We employed an unbiased high-throughput lethality screen using a 24,088 siRNA library targeting over 6,000 druggable genes and studied their effects on growth and/or survival of epithelial ovarian cancer (EOC) cell lines. The top 300 “hits” affecting the viability of A1847 cells were rescreened across additional EOC cell lines and non-tumorigenic, human immortalized ovarian epithelial cell lines. Fifty-three gene candidates were found to exhibit effects in all tumorigenic cell lines tested. Extensive validation of these hits refined the list to four high quality candidates (HSPA5, NDC80, NUF2, and PTN). Mechanistic studies show that silencing of three genes leads to increased apoptosis, while HSPA5 silencing appears to alter cell growth through G1 cell cycle arrest. Furthermore, two independent gene expression studies show that NDC80, NUF2 and PTN were significantly aberrantly overexpressed in serous adenocarcinomas. Overall, our functional genomics results integrated with the genomics data provide an important unbiased avenue towards the identification of prospective therapeutic targets for drug discovery, which is an urgent and unmet clinical need for ovarian cancer.

Comparison of growth factor signalling pathway utilisation in cultured normal melanocytes and melanoma cell lines

BACKGROUND

The phosphatidylinositol-3-kinase (PI3K-PKB), mitogen activated protein kinase (MEK-ERK) and the mammalian target of rapamycin (mTOR- p70S6K), are thought to regulate many aspects of tumour cell proliferation and survival. We have examined the utilisation of these three signalling pathways in a number of cell lines derived from patients with metastatic malignant melanoma of known PIK3CA, PTEN, NRAS and BRAF mutational status.

METHODS

Western blotting was used to compare the phosphorylation status of components of the PI3K-PKB, MEK-ERK and mTOR-p70S6K signalling pathways, as indices of pathway utilisation.

RESULTS

Normal melanocytes could not be distinguished from melanoma cells on the basis of pathway utilisation when grown in the presence of serum, but could be distinguished upon serum starvation, where signalling protein phosphorylation was generally abrogated. Surprisingly, the differential utilisation of individual pathways was not consistently associated with the presence of an oncogenic or tumour suppressor mutation of genes in these pathways.

CONCLUSION

Utilisation of the PI3K-PKB, MEK-ERK and mTOR-p70S6K signalling pathways in melanoma, as determined by phosphorylation of signalling components, varies widely across a series of cell lines, and does not directly reflect mutation of genes coding these components. The main difference between cultured normal melanocytes and melanoma cells is not the pathway utilisation itself, but rather in the serum dependence of pathway utilisation.