The p75NTR neurotrophin receptor is a tumor suppressor in human and murine retinoblastoma development

MicroRNA-34b-5p inhibits proliferation, stemness, migration and invasion of retinoblastoma cells via Notch signaling

Retinoblastoma (RB) is one of the most common forms of childhood intraocular cancer. While the occurrence of RB is traditionally associated with dysregulation of the RB1 gene, efforts have been made to assess the role of several other pathways that may result in RB. The Notch signaling pathway has been identified as one of the sentinel pathways in retinal development and has been indicated to serve as a tumor suppressor. However, epigenetic modifications of the Notch signaling pathway, and their consequences on tumor establishment and progression, have received little attention. The present study attempted to elucidate the microRNA (miR)-mediated dysregulation of the Notch signaling pathway and its implications on tumor initiation. Upon recruitment of patients with RB (age, 4-25 months), the levels of miR-34b-5p were determined in tumor and adjacent healthy tissues. Simultaneously, the serum levels of miR-34b-5p were measured in tumor and healthy samples using reverse transcriptase-quantitative PCR (RT-qPCR). Binding of miR-34b-5p to Notch1 and Notch2 were confirmed bioinformatically. In vitro studies were performed in Y79 and Weri-Rb-1 RB cell lines. The cell lines were transfected with miR-34b-5p constructs and miR-34b-5p overexpression was confirmed using RT-qPCR. The impact of miR-34b-5p overexpression on cell growth and cancer stemness markers (Sox-2, Nanog, and CD133) was examined. The expression levels of Notch1 and Notch2 were evaluated in the presence of miR-34b-5p. The rescue of cell growth and cancer stemness phenotypes was evaluated by co-transfection of miR-34b-5p with Notch1 or Notch2. The results of the present study indicated that the expression levels of miR-34b-5p were reduced in patient tissues and serum samples compared with those in healthy tissues and samples. Notch1 and Notch2 expression level was negatively correlated with the expression level of miR-34b-5p. Overexpression of miR-34b-5p resulted in reduced cell proliferation, migration, invasion and cancer stemness compared with the control group. Further in vivo experiments confirmed the inhibitory effects of miR-34b-5p on RB cell proliferation. Upon co-transfection of miR-34b-5p with Notch1 or Notch2, these phenotypes were rescued with reversal of cell growth and tumor sphere formation. Collectively, the results indicated that miR-34b-5p functions as a tumor suppressor in RB via regulating the Notch signaling pathway. Therefore, miR-34b-5p may be explored for its utility as a therapeutic target in RB.

Resistance to targeted treatment of gastroenteropancreatic neuroendocrine tumors

The mammalian target of rapamycin (mTOR) is part of the phosphoinositide-3-kinase (PI3K)/protein kinase B (Akt)/mTOR signaling. The PI3K/Akt/mTOR pathway has a pivotal role in the oncogenesis of neuroendocrine tumors (NETs). In addition, vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) drive angiogenesis in NETs and therefore contributes to neuroendocrine tumor development. Hence, mTOR and angiogenesis inhibitors have been developed. Everolimus, a first-generation mTOR inhibitor, has shown significant survival benefit in advanced gastroenteropancreatic NETs. Sunitinib, a pan-tyrosine kinase inhibitor that targets the VEGF receptor, has proven to increase progression-free survival in advanced pancreatic NETs. Nevertheless, primary and acquired resistance to rapalogs and sunitinib has limited the clinical benefit for NET patients. Despite the identification of multiple molecular mechanisms of resistance, no predictive biomarker has made it to the clinic. This review is focused on the mTOR signaling and angiogenesis in NET, the molecular mechanisms of primary and acquired resistance to everolimus and sunitinib and how to overcome this resistance by alternative drug compounds.

Bigh3 silencing increases retinoblastoma tumor growth in the murine SV40-TAg-Rb model

BIGH3, a secreted protein of the extracellular matrix interacts with collagen and integrins on the cell surface. BIGH3 can have opposing functions in cancer, acting either as tumor suppressor or promoter by enhancing tumor progression and angiogenesis. In the eye, BIGH3 is expressed in the cornea and the retinal pigment epithelium and could impact on the development of retinoblastoma, the most common paediatric intraocular neoplasm. Retinoblastoma initiation requires the inactivation of both alleles of the RB1 tumor suppressor gene in the developing retina and tumor progression involves additional genomic changes. To determine whether BIGH3 affects retinoblastoma development, we generated a retinoblastoma mouse model with disruption of the Bigh3 genomic locus. Bigh3 silencing in these mice resulted in enhanced tumor development in the retina. A decrease in apoptosis is involved in the initial events of tumorigenesis, followed by an increased activity of the pro-survival ERK pathway as well as an upregulation of cyclin-dependent kinases (CDKs). Taken together, these data suggest that BIGH3 acts as a tumor suppressor in the retina.

Generation and characterization of a human oral squamous carcinoma cell line SCC-9 with CRISPR/Cas9-mediated deletion of the p75 neurotrophin receptor

OBJECTIVE

To investigate the importance of the p75 neurotrophin receptor (p75^NTR) in human tongue squamous carcinoma cells, we exploited the CRISPR/Cas9 technology to establish a p75^NTR-knockout SCC-9 cell line and to explore the effect on biological functions.

MATERIALS AND METHODS

The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated endonuclease (Cas9) system was used to generate genomic deletion mutants of p75^NTR in the tongue squamous carcinoma cell lines SCC-9. Single-guide RNA (sgRNA) sequences were designed to target the p75^NTR genomic sequence and were cloned into plasmid pGK1.1. The linearized vector was electroporated into SCC-9 cells and p75^NTR deletion was confirmed using Cruiser™ enzyme digestion and PCR amplification. SCC-9 clones with successful deletion of p75^NTR were identified and verified by sequencing and selected for functional testing in cell proliferation, invasion, migration, and colony-forming assays.

RESULTS

Compared with control cells, p75^NTR-knockout SCC-9 cells showed significantly diminished abilities to proliferate, invade, migrate, and form colonies, indicating a reduction in pro-tumorigenic behavior.

CONCLUSION

These data demonstrate, first, that the CRISPR/Cas9 system is a simplified method for generating p75^NTR knockouts with relatively high efficiency, and second, that deletion of p75^NTR suppresses several tumor-promoting properties of SCC-9 cells, suggesting that p75^NTR is a potential target for the development of novel therapies for tongue cancer.

Synergistic activity of everolimus and 5-aza-2'-deoxycytidine in medullary thyroid carcinoma cell lines

Medullary thyroid cancer (MTC) is a tumor highly resistant to chemo‐ and radiotherapy. Drug resistance can be induced by epigenetic changes such as aberrant DNA methylation. To overcome drug resistance, we explored a promising approach based on the use of 5‐aza‐2′‐deoxycytidine (AZA), a demethylating agent, in combination with the mTOR inhibitor everolimus in MTC cells (MZ‐CRC‐1 and TT). This combined treatment showed a strong synergistic antiproliferative activity through the induction of apoptosis. The effect of everolimus and/or AZA on genome‐wide expression profiling was evaluated by Illumina BeadChip in MZ‐CRC‐1 cells. An innovative bioinformatic pipeline identified four potential molecular pathways implicated in the synergy between AZA and everolimus: PI3K‐Akt signaling, the neurotrophin pathway, ECM/receptor interaction, and focal adhesion. Among these, the neurotrophin signaling pathway was most directly involved in apoptosis, through the overexpression of NGFR and Bax genes. The increased expression of genes involved in the NGFR‐MAPK10‐TP53‐Bax/Bcl2 pathway during incubation with AZA plus everolimus was validated by western blotting in MZ‐CRC‐1 cells. Interestingly, addition of a neutralizing anti‐NGFR antibody inhibited the synergistic cytotoxic activity between AZA and everolimus. These results open a new therapeutic scenario for MTC and potentially other neuroendocrine tumors, where therapy with mTOR inhibitors is currently approved.

p75 neurotrophin receptor: A potential surface marker of tongue squamous cell carcinoma stem cells

The present study detected p75 neurotrophin receptor (p75^NTR) expression in tongue squamous cell carcinoma (TSCC) cell lines, in order to define the biological properties of p75^NTR+ cells and to confirm the use of p75^NTR+ as a surface marker for TSCC stem cells. p75^NTR+ cells were separated from Tca-8113 and CAL-27 TSCC cells by fluorescence-activated cell sorting. Colony formation, MTT and scratch assays, and a tumorigenicity analysis were performed to measure self-renewal and proliferation, multidirectional differentiation, and tumorigenicity of p75^NTR+ cells. p75^NTR+ cells comprised 3.1 and 1.9% of Tca-8113 and CAL-27 cells (mean of three experiments), respectively, and were more able to form colonies compared with non-sorted cells (P<0.01). In addition, the proportion of p75^NTR+ cells generated from monoclonal p75^NTR+ cells decreased to 14.5 (Tca-8113) and 5.8% (CAL-27) of cells within 2 weeks, thus suggesting that p75^NTR+ cells are able to generate p75^NTR+ and p75^NTR− cells. Furthermore, p75^NTR+ cells exhibited increased proliferation, as evidenced by MTT assay (P<0.01) and had greater metastatic ability according to the scratch assay (P<0.01), compared with non-sorted cells. p75^NTR+ cells also exhibited a greater tumorigenic capacity compared with non-sorted cells. In conclusion, p75^NTR+ cells isolated from TSCC cell lines possess the characteristics of cancer stem cells; therefore, p75^NTR may be considered a useful surface marker for the identification of TSCC stem cells.

Kif14 overexpression accelerates murine retinoblastoma development

The mitotic kinesin KIF14 has an essential role in the recruitment of proteins required for the final stages of cytokinesis. Genomic gain and/or overexpression of KIF14 has been documented in retinoblastoma and a number of other cancers, such as breast, lung and ovarian carcinomas, strongly suggesting its role as an oncogene. Despite evidence of oncogenic properties in vitro and in xenografts, Kif14's role in tumor progression has not previously been studied in a transgenic cancer model. Using a novel Kif14 overexpressing, simian virus 40 large T-antigen retinoblastoma (TAg-RB) double transgenic mouse model, we aimed to determine Kif14's role in promoting retinal tumor formation. Tumor initiation and development in double transgenics and control TAg-RB littermates were documented in vivo over a time course by optical coherence tomography, with subsequent ex vivo quantification of tumor burden. Kif14 overexpression led to an accelerated initiation of tumor formation in the TAg-RB model and a significantly decreased tumor doubling time (1.8 vs. 2.9 weeks). Moreover, overall percentage tumor burden was also increased by Kif14 overexpression. These data provide the first evidence that Kif14 can promote tumor formation in susceptible cells in vivo.

Experimental verification of a predicted intronic microRNA in human NGFR gene with a potential pro-apoptotic function

Neurotrophins (NTs) are a family of secreted growth factor proteins primarily involved in the regulation of survival and appropriate development of neural cells, functioning by binding to their specific (TrkA, TtkB, and TrkC) and/or common NGFR receptor. NGFR is the common receptor of NTs, binding with low-affinity to all members of the family. Among different functions assigned to NGFR, it is also involved in apoptosis induction and tumorigenesis processes. Interestingly, some of the functions of NGFR appear to be ligand-independent, suggesting a probable involvement of non-coding RNA residing within the sequence of the gene. Here, we are reporting the existence of a conserved putative microRNA, named Hsa-mir-6165 [EBI accession#: FR873488]. Transfection of a DNA segment corresponding to the pre-mir-6165 sequence in Hela cell line caused the generation of mature exogenous mir-6165 (a ∼200,000 fold overexpression). Furthermore, using specific primers, we succeeded to detect the endogenous expression of mir-6165 in several glioma cell lines and glioma primary tumors known to express NGFR. Similar to the pro-apoptotic role of NGFR in some cell types, overexpression of pre-mir-6165 in U87 cell line resulted in an elevated rate of apoptosis. Moreover, coordinated with the increased level of mir-6165 in the transfected U87 cell line, two of its predicted target genes (Pkd1 and DAGLA) were significantly down-regulated. The latter findings suggest that some of the previously attributed functions of NGFR could be explained indirectly by co-transcription of mir-6165 in the cells.

The Bcl-2/Bcl-XL inhibitor ABT-737 promotes death of retinoblastoma cancer cells

PURPOSE

Retinoblastoma is a malignant tumor that usually develops in early childhood. During retinoblastoma spreading, RB1 gene inactivation is followed by additional genomic modifications which progressively lead to resistance of tumor cells to death. Drugs that act at downstream levels of death signaling pathways should therefore be interesting in killing retinoblastoma cells. ABT-737, a BH3 mimetic molecule effective at the mitochondrial level, has been shown to induce apoptosis in different human tumoral cell lines as well as in primary patient-derived cells, and in a mouse xenograph model.

METHODS

In this report, we analyzed the pro-death effect of ABT-737 on two human retinoblastoma cell lines, Y79 and WERI-Rb, as well as on the mouse photoreceptor cell line 661W.

RESULTS

We observed that ABT-737 was very effective as a single agent in inducing human WERI-Rb cells apoptosis without affecting the mouse 661W photoreceptor cells. However human Y79 cells were resistant to ABT-737, as a probable consequence of the absence of Bax. The high sensitivity of WERI-Rb to ABT-737 can be increased by downregulating Mcl-1 using the proteasome inhibitor MG-132. Preliminary analysis in primary mouse retinoblastoma tumoral cell lines predicts high sensitivity to ABT-737.

CONCLUSION

Our data suggest that ABT-737 or related compounds could be a highly effective drug in the treatment of some retinoblastomas.

Retinoblastoma: Recent trends A mini review based on published literature

Retinoblastoma (RB) is the most common intraocular malignancy in children. Recently, there have been significant advances made in the molecular pathology and the management of the disease. Last decade has witnessed better understanding of the genetics of RB, the discovery of new tumor markers expressed by the RB tumors, the identification of high-risk histopathological factors following enucleation, and newer methods of treatment including periocular chemotherapy and superselective intraarterial chemotherapy. All these advances have translated in improved survival rates for the affected children, improved rates of eye salvage, and improved visual outcomes. This article briefly reviews these advances.Method of Literature Search: Literature on the Medline database was searched using the PubMed interface. The search strategy included MeSH and natural language terms using the keywords mentioned. Reference lists in retrieved articles and textbooks were also searched for relevant references.

Molecular pathology of retinoblastoma

Retinoblastoma (RB) is an embryonic neoplasm of retinal origin. For many years, scientists have sought the fundamental origins of tumorigenesis, with the ultimate hope of discovering a cure. Indeed, these efforts have led to a significant understanding that multiple molecular and genetic aberrations, such as uncontrolled proliferation and the inhibition of apoptosis that contribute to the canonical characteristics of tumor biology. Despite these advances, a thorough understanding, such as the precise cells, which are the targets of neoplastic transformation, especially in solid tumors, is currently lacking. The focus of this review is to emphasize the molecular defects involved in the RB tumor progression and mechanisms associated with inhibition of tumor cell apoptotic processes. This review also discusses the importance of target molecules characterization and their potential therapeutic or prognostic use in RB disease.

Crosstalk between c-Jun and TAp73alpha/beta contributes to the apoptosis-survival balance

The p53-family member p73 plays a role in various cellular signaling pathways during development and growth control and it can have tumor suppressor properties. Several isoforms of p73 exist with considerable differences in their function. Whereas the functions of the N-terminal isoforms (TA and ΔNp73) and their opposing pro- and antiapoptotic roles have become evident, the functional differences of the distinct C-terminal splice forms of TAp73 have remained unclear. Here, we characterized the global genomic binding sites for TAp73α and TAp73β by chromatin immunoprecipitation sequencing as well as the transcriptional responses by performing RNA sequencing. We identified a specific p73 consensus binding motif and found a strong enrichment of AP1 motifs in close proximity to binding sites for TAp73α. These AP1 motif-containing target genes are selectively upregulated by TAp73α, while their mRNA expression is repressed upon TAp73β induction. We show that their expression is dependent on endogenous c-Jun and that recruitment of c-Jun to the respective AP1 sites was impaired upon TAp73β expression, in part due to downregulation of c-Jun. Several of these AP1-site containing TAp73α-induced genes impinge on apoptosis induction, suggesting an underlying molecular mechanism for the observed functional differences between TAp73α and TAp73β.

Array-based comparative genomic hybridization identifies CDK4 and FOXM1 alterations as independent predictors of survival in malignant peripheral nerve sheath tumor

PURPOSE

Malignant peripheral nerve sheath tumors (MPNST) are highly aggressive sarcomas with variable patient survival and few known prognostically relevant genomic biomarkers. To identify survival-associated genomic biomarkers, we performed high-resolution array-based comparative genomic hybridization (aCGH) on a large set of MPNSTs.

EXPERIMENTAL DESIGN

Candidate gene alterations identified by aCGH in 38 MPNSTs were validated at the DNA, RNA, and protein levels on these same tumors and an independent set of 87 MPNST specimens.

RESULTS

aCGH revealed highly complex copy number alterations, including both previously reported and completely novel loci. Four regions of copy number gain were associated with poor patient survival. Candidate genes in these regions include SOX5 (12p12.1), NOL1 and MLF2 (12p13.31), FOXM1 and FKBP1 (12p13.33), and CDK4 and TSPAN31 (12q14.1). Alterations of these candidate genes and several others of interest (ERBB2, MYC and TP53) were confirmed by at least 1 complementary methodology, including DNA and mRNA quantitative real-time PCR, mRNA expression profiling, and tissue microarray-based fluorescence in situ hybridization and immunohistochemistry. Multivariate analysis showed that CDK4 gain/amplification and increased FOXM1 protein expression were the most significant independent predictors for poor survival in MPNST patients (P < 0.05).

CONCLUSIONS

Our study provides new and independently confirmed candidate genes that could serve as genomic biomarkers for overall survival in MPNST patients.

Cdh11 acts as a tumor suppressor in a murine retinoblastoma model by facilitating tumor cell death

CDH11 gene copy number and expression are frequently lost in human retinoblastomas and in retinoblastomas arising in TAg-RB mice. To determine the effect of Cdh11 loss in tumorigenesis, we crossed Cdh11 null mice with TAg-RB mice. Loss of Cdh11 had no gross morphological effect on the developing retina of Cdh11 knockout mice, but led to larger retinal volumes in mice crossed with TAg-RB mice (p = 0.01). Mice null for Cdh11 presented with fewer TAg-positive cells at postnatal day 8 (PND8) (p = 0.01) and had fewer multifocal tumors at PND28 (p = 0.016), compared to mice with normal Cdh11 alleles. However, tumor growth was faster in Cdh11-null mice between PND8 and PND84 (p = 0.003). In tumors of Cdh11-null mice, cell death was decreased 5- to 10-fold (p<0.03 for all markers), while proliferation in vivo remained unaffected (p = 0.121). Activated caspase-3 was significantly decreased and β-catenin expression increased in Cdh11 knockdown experiments in vitro. These data suggest that Cdh11 displays tumor suppressor properties in vivo and in vitro in murine retinoblastoma through promotion of cell death.

Despite over two decades since loss of RB1 was implicated in initiating retinoblastoma, the unique tissue specificity of this process remains puzzling. Indeed, functional loss of both alleles of the RB1 tumor suppressor gene results in >40,000-fold increase in predisposition to retinal cancer during childhood, while one constitutional RB1 mutant allele confers a broader but much lower cancer predisposition later in life. We have proposed a specific signature of progressive genomic changes that leads to full tumor development. One of these changes is genomic loss of the CDH11 gene, suggesting that this gene normally suppresses the development of retinoblastoma. We present novel data indicating that Cdh11 functions as a tumor suppressor gene in retinoblastoma by facilitating cell death. Our insight into the sequence of events that contribute to retinoblastoma development is important for future therapies and fundamental understanding of cancer.

Molecular karyotype of sporadic unilateral retinoblastoma tumors

BACKGROUND

Retinoblastoma (RB) is a childhood ocular malignancy associated with mutations in RB1, a tumor susceptibility gene. Inactivation of both copies of the RB1 gene in a retinal cell is followed by the sequential acquisition of additional genetic changes that define the course to tumor formation.

METHODS

To identify the genetic events that cooperate with loss of the RB1 gene function, we performed a whole genome sampling assay based on single nucleotide polymorphism genotyping. We used DNA isolated from 25 sporadic, unilateral RB tumors and matched blood samples.

RESULTS

Genomic profiles were analyzed to identify regions of loss of heterozygosity or amplification. Two major subclasses of RB tumors were defined by the presence (n = 18) or absence (n = 7) of loss of heterozygosity of chromosome 13. Loss of heterozygosity in most cases was the result of copy-neutral events caused by mitotic recombination and mitotic nondisjunction. Tumors harbored novel regions of amplification at 1q44, 3p25, 11q14, 11q25, 14q23, 15q21, 16p13, 17p11.2, 19q13, and 20q13, whereas regions of loss included 6q22, 7q21, and 21q2.

CONCLUSION

Whole genome sampling assay-based analysis of unilateral RB tumors revealed novel regions as significant. These minimum critical regions that are lost or amplified are expected to harbor genes that aid the process of tumorigenesis.

Quantitative analysis of tumor size in a murine model of retinoblastoma

Murine models can provide valuable insight into mechanisms of tumorigenesis. Tumor size is often used to assess the impact of genetic insult or therapeutic treatment, usually using in vivo imaging of advanced tumors. We now describe a highly sensitive method to quantify tumor volume in a mouse model of retinoblastoma, from the earliest stages of tumor initiation to large, advanced tumors. This methodology combines immunohistochemistry, digital slide scanning and computer image analysis, and can be applied to quantitatively assess and characterize early tumor development in other models.

The low-affinity neurotrophin receptor, p75, is upregulated in ganglioneuroblastoma/ganglioneuroma and reduces tumorigenicity of neuroblastoma cells in vivo

Neuroblastoma, the most common extracranial tumor of childhood, is derived from neural crest progenitor cells that fail to differentiate along their predefined route to sympathetic neurons or sympatho-adrenergic adrenal cells. Although expression of the high-affinity neurotrophin receptors, TrkA and TrkB, is of major importance in neuroblastoma, the significance of the expression of the low-affinity neurotrophin receptor, p75, is unclear. Here, we analyzed immunohistochemically expression of p75 on a tissue microarray of 93 primary neuroblastic tumors and assessed the functional consequences of p75 expression in neuroblastoma cell lines. We found the p75 receptor protein to be expressed in neuroblastic cells of ganglioneuromas/ganglioneuroblastomas as well as differentiating neuroblastomas, but not in poorly differentiated neuroblastomas. In an unrelated cohort of 110 neuroblastic tumors, p75 mRNA expression levels correlated with differentiation, and patients with tumors that expressed p75 at high levels had an increased event-free and overall survival. In addition, we did not detect p75 expression in 8 established neuroblastoma cell lines examined with FACS analysis. These cell lines exhibited an undifferentiated morphology, and were all derived from aggressive, high-stage neuroblastomas. Ectopic p75 expression in the SH-SY5Y neuroblastoma cell line significantly reduced proliferation, increased the fraction of apoptotic cells in vitro and resulted in a loss of tumorigenicity in nude mice. Taken together, our data suggest that expression of the p75 low-affinity neurotrophin receptor is correlated with a reduced level of tumorigenicity, and that induction of p75 expression may be an option to revert features of an aggressive tumor phenotype.

Renal tumor natural history: the rationale and role for active surveillance

Renal cell carcinoma (RCC) is the most common malignancy of the kidney. Despite widespread treatment at diagnosis, overall mortality rates associated with RCC have not decreased. Partly because of the more frequent use of abdominal imaging, diagnosis as an incidental finding has increased. The largest increase in incidence is in tumors smaller than 4 cm, termed small renal masses (SRMs). SRMs that are RCC may frequently be growth slowly and have a low risk of early progression. Initial active surveillance with delayed treatment for progression for selected patients should be considered. This should result in an overall decrease in treatment burden and cost saving.

Insights from mouse models into human retinoblastoma

Novel murine models of retinoblastoma based on Rb gene deletion in concert with inactivation of Rb family members have recently been developed. These new Rb knockout models of retinoblastoma provide excellent tools for pre-clinical studies and for the exploration of the genetics of tumorigenesis driven by RB inactivation. This review focuses on the developmental consequences of Rb deletion in the retina and the genetic interactions between Rb and the two other members of the pocket protein family, p107 (Rbl1) and p130 (Rbl2). There is increasing appreciation that homozygous RB mutations are insufficient for human retinoblastoma. Identifying and understanding secondary gene alterations that cooperate with RB inactivation in tumorigenesis may be facilitated by mouse models. Recent investigation of the p53 pathway in retinoblastoma, and evidence of spatial topology to early murine retinoblastoma are also discussed in this review.