Dysfunctional p53 deletion mutants in cell lines derived from Hodgkin's lymphoma

Increased STAT expression in Reed-Sternberg cells as a potential positive prognostication biomarker in Hodgkin lymphoma

Classic Hodgkin lymphoma (cHL) prognostication primarily relies on clinical and radiological factors. Despite this, a subset of patients still progress. Immunohistochemistry (IHC) based biomarkers on diagnostic tissue have not been routinely used for prognostication. A multicentre retrospective analysis identified 62 patients with cHL. IHC on diagnostic tissues was used to stain Reed-Sternberg cells (RS) cells for STAT1, pSTAT3, p53 and tumour microenvironment for CD68 and PD-1. IHC stains were scored by anatomical pathologists blinded to patients and their outcomes and correlated with survival. Strong intensity of STAT1 and pSTAT3 staining correlated with improved overall survival (OS), with hazard ratios (HR) of 0.21 [95% confidence interval (CI) 0.06-0.76] and 0.22 (95% CI 0.06-0.84), respectively. Similarly, the median OS for weak versus strong STAT1 or pSTAT3 staining was 8.8 years versus not reached. Other IHC stains did not correlate with prognosis. In this cohort of cHL patients, downregulation of immunohistochemical STAT1 or pSTAT3 in RS cells is associated with inferior OS, suggesting STAT transcription within the pathognomonic RS cells may have tumour suppressor function and may be a potential biomarker for cHL prognosis.

Apoptotic regulator BCL-2 blockade as a potential therapy in classical Hodgkin Lymphoma

The challenge in classical Hodgkin Lymphoma (cHL) management is the 30-40% of refractory/relapsed cases.

AIMS

The aim of this work was to determine whether NIK and BCL-2 could be useful as prognosis biomarkers in cHL. In addition, we evaluated BCL-2 as a directed-therapy in cHL cell lines using venetoclax.

MAIN METHODS

We evaluated NIK and BCL-2 expression in 112 untreated cHL patients' lymph-node biopsies by immunohistochemistry. cHL cell lines were treated with venetoclax alone or combined with vincristine or doxorubicin. Cell viability, metabolic activity and cell death were analyzed by trypan-blue exclusion method, MTS assay and FDA/IP staining respectively.

KEY FINDINGS

No correlation between NIK or BCL-2 expression and the majority of the clinical parameters was found. Patients with ≥60% BCL-2+ HRS-cells had a shorter disease-free survival (DFS) and overall survival (OS) (p = 0.002, p = 0.02 respectively). A decision tree analysis, in a 30 patients subgroup, showed that patients with <60% NIK+ HRS-cells but with ≥60% BCL-2+ HRS-cells had a worse outcome in terms of DFS and OS. These parameters performed better as prognosis indicators as compared to the diagnosis bone marrow status. Human cHL cell lines U-H01, KM-H2, L1236, SUPHD1, L540 showed sensitivity to venetoclax. The co-treatment effect of venetoclax and vincristine or doxorubicin on cell viability was diverse depending on the cell line evaluated.

SIGNIFICANCE

BCL-2 should be considered as a prognosis biomarker as well as a potential new therapeutic target in cHL. We report for the first time the cytotoxic effect of venetoclax in human cHL cell lines.

ASH2L drives proliferation and sensitivity to bleomycin and other genotoxins in Hodgkin's lymphoma and testicular cancer cells

It is of clinical importance to identify biomarkers predicting the efficacy of DNA damaging drugs (genotoxins) so that nonresponders are not unduly exposed to the deleterious effects of otherwise inefficient drugs. Here, we initially focused on the bleomycin genotoxin because of the limited information about the genes implicated in the sensitivity or resistance to this compound. Using a whole-genome CRISPR/Cas9 gene knockout approach, we identified ASH2L, a core component of the H3K4 methyl transferase complex, as a protein required for bleomycin sensitivity in L1236 Hodgkin lymphoma. Knocking down ASH2L in these cells and in the NT2D1 testicular cancer cell line rendered them resistant to bleomycin, etoposide, and cisplatin but did not affect their sensitivity toward ATM or ATR inhibitors. ASH2L knockdown decreased cell proliferation and facilitated DNA repair via homologous recombination and nonhomologous end-joining mechanisms. Data from the Tumor Cancer Genome Atlas indicate that patients with testicular cancer carrying alterations in the ASH2L gene are more likely to relapse than patients with unaltered ASH2L genes. The cell models we have used are derived from cancers currently treated either partially (Hodgkin’s lymphoma), or entirely (testicular cancer) with genotoxins. For such cancers, ASH2L levels could be used as a biomarker to predict the response to genotoxins. In situations where tumors are expressing low levels of ASH2L, which may allow them to resist genotoxic treatment, the use of ATR or ATM inhibitors may be more efficacious as our data indicate that ASH2L knockdown does not affect sensitivity to these inhibitors.

Independent Mechanisms Lead to Genomic Instability in Hodgkin Lymphoma: Microsatellite or Chromosomal Instability †

Background: Microsatellite and chromosomal instability have been investigated in Hodgkin lymphoma (HL). Materials and Methods: We studied seven HL cell lines (five Nodular Sclerosis (NS) and two Mixed Cellularity (MC)) and patient peripheral blood lymphocytes (100 NS-HL and 23 MC-HL). Microsatellite instability (MSI) was assessed by PCR. Chromosomal instability and telomere dysfunction were investigated by FISH. DNA repair mechanisms were studied by transcriptomic and molecular approaches. Results: In the cell lines, we observed high MSI in L428 (4/5), KMH2, and HDLM2 (3/5), low MSI in L540, L591, and SUP-HD1, and none in L1236. NS-HL cell lines showed telomere shortening, associated with alterations of nuclear shape. Small cells were characterized by telomere loss and deletion, leading to chromosomal fusion, large nucleoplasmic bridges, and breakage/fusion/bridge (B/F/B) cycles, leading to chromosomal instability. The MC-HL cell lines showed substantial heterogeneity of telomere length. Intrachromosmal double strand breaks induced dicentric chromosome formation, high levels of micronucleus formation, and small nucleoplasmic bridges. B/F/B cycles induced complex chromosomal rearrangements. We observed a similar pattern in circulating lymphocytes of NS-HL and MC-HL patients. Transcriptome analysis confirmed the differences in the DNA repair pathways between the NS and MC cell lines. In addition, the NS-HL cell lines were radiosensitive and the MC-cell lines resistant to apoptosis after radiation exposure. Conclusions: In mononuclear NS-HL cells, loss of telomere integrity may present the first step in the ongoing process of chromosomal instability. Here, we identified, MSI as an additional mechanism for genomic instability in HL.

Detection of homozygous deletions in tumor-suppressor genes ranging from dozen to hundreds nucleotides in cancer models

Tumor-suppressor genes can be inactivated by several mechanisms and, in a majority of cases, both alleles need to be affected. One of the mechanisms of inactivation is due to deletions ranging from dozen to hundreds of nucleotides; such deletions are often missed by variant callers. HomDelDetect is a method to detect such homozygous deletions in cancer models, such as cancer cell lines and potentially patient tumor-derived xenografts. This method can be applied to partial exome, whole-exome sequencing, whole-genome sequencing, and RNA-seq data. We applied our method across a panel of CCLE cancer cell lines and observed good concordance with SNP array-based analysis and also detected deletions that have been missed by variant callers and by SNP arrays, demonstrating the ability of HomDelDetect to improve the annotations of tumor-suppressor genes in cancer models.

miR-24-3p Is Overexpressed in Hodgkin Lymphoma and Protects Hodgkin and Reed-Sternberg Cells from Apoptosis

miRNAs play important roles in biological processes, such as proliferation, metabolism, differentiation, and apoptosis, whereas altered expression levels contribute to diseases, such as cancers. We identified miRNAs with aberrant expression in Hodgkin lymphoma (HL) and investigated their role in pathogenesis. Small RNA sequencing revealed 84 significantly differentially expressed miRNAs in HL cell lines as compared to germinal center B cells. Three up-regulated miRNAs-miR-23a-3p, miR-24-3p, and miR-27a-3p-were derived from one primary miRNA transcript. Loss-of-function analyses for these miRNAs and their seed family members resulted in decreased growth on miR-24-3p inhibition in three HL cell lines and of miR-27a/b-3p inhibition in one HL cell line. Apoptosis analysis indicated that the effect of miR-24-3p on cell growth is at least in part caused by an increase of apoptotic cells. Argonaute 2 immunoprecipitation revealed 1142 genes consistently targeted by miRNAs in at least three of four HL cell lines. Furthermore, 52 of the 1142 genes were predicted targets of miR-24-3p. Functional annotation analysis revealed a function related to cell growth, cell death, and/or apoptosis for 15 of the 52 genes. Western blotting of the top five genes showed increased protein levels on miR-24-3p inhibition for CDKN1B/P27^kip1 and MYC. In summary, we showed that miR-24-3p is up-regulated in HL and its inhibition impairs cell growth possibly via targeting CDKN1B/P27^kip1 and MYC.

Characterization of Alstrom Syndrome 1 (ALMS1) Transcript Variants in Hodgkin Lymphoma Cells

The Alstrom syndrome gene (ALMS1) is one of the largest disease associated genes identified today in the human genome and is implicated in cell cycle control, ciliogenesis, endosome recycling and intracellular transport mechanisms. ALMS1 mutations cause Alstrom syndrome, a rare genetic disorder. However, its function is not completely understood. DNA microarray analysis suggested that ALMS1 might be differentially expressed between Hodgkin lymphoma (HL) cells and normal tissues. By using reverse transcription-polymerase chain reaction (RT-PCR) we detected low but variable expression of ALMS1 in HL cell lines with highest expression in KM-H2 cells. Immunofluorescence indicated centrosomal accumulation of ALMS1 protein in HL cells. Knock-down of ALMS1 in KM-H2 cells had no impact on viability or cytotoxic drug sensitivity of these cells. Sequencing of RT-PCR products from HL cell lines identified three variable regions in ALMS1 transcripts that affect exons 2, 13, and 23. One of these variants was characterized by splicing out of exon 13. The other variants are characterized by two alternative 5 prime ends or alternative 3 prime ends. Structure prediction of the corresponding RNAs and proteins suggest that the different transcript variants might affect posttranscriptional regulation and ligand binding.

Recurrent genetic defects in classical Hodgkin lymphoma cell lines

Genetic analysis of classical Hodgkin lymphoma (cHL) has been hampered by the paucity of Hodgkin cells in biopsies and their poor growth in vitro. However, a wealth of information has been obtained from cHL cell lines. Here we report results of whole-exome sequencing and karyotypic analysis of five cHL cell lines. Four genes with potentially pathogenic single nucleotide variants (SNV) were detected in three cell lines. SNV were also detected in seventeen HL-related genes and three mitosis-related genes. Copy number variants were detected in four HL-related genes in all five cell lines. Given the high degree of aneuploidy in HL, mitosis-related genes were screened for defects. One mitotic gene (NCAPD2) was amplified in all five HL cell lines, and two genes (FAM190A, PLK4) were amplified in four cell lines. These results suggest that genomic instability of HL may be due to defects in genes involved in chromosome duplication and segregation.

The traditional Chinese medical compound Rocaglamide protects nonmalignant primary cells from DNA damage-induced toxicity by inhibition of p53 expression

One of the main obstacles of conventional anticancer therapy is the toxicity of chemotherapeutics to normal tissues. So far, clinical approaches that aim to specifically reduce chemotherapy-mediated toxicities are rare. Recently, a number of studies have demonstrated that herbal extracts derived from traditional Chinese medicine (TCM) may reduce chemotherapy-induced side effects. Thus, we screened a panel of published cancer-inhibiting TCM compounds for their chemoprotective potential and identified the phytochemical Rocaglamide (Roc-A) as a candidate. We show that Roc-A significantly reduces apoptotic cell death induced by DNA-damaging anticancer drugs in primary human and murine cells. Investigation of the molecular mechanism of Roc-A-mediated protection revealed that Roc-A specifically blocks DNA damage-induced upregulation of the transcription factor p53 by inhibiting its protein synthesis. The essential role of p53 in Roc-A-mediated protection was confirmed by siRNA knockdown of p53 and by comparison of the effects of Roc-A on chemoprotection of splenocytes isolated from wild-type and p53-deficient mice. Importantly, Roc-A did not protect p53-deficient or -mutated cancer cells. Our data suggest that Roc-A may be used as an adjuvant to reduce the side effects of chemotherapy in patients with p53-deficient or -mutated tumors.

MicroRNA and gene networks in human Hodgkin's lymphoma

There has been significant progress in gene and microRNA (miRNA) research with regard to the morbidity of Hodgkin's lymphoma (HL). However, the regulatory mechanisms of genes and miRNAs have yet to be determined. In the current study, the regulatory association between genes, miRNAs and transcription factors (TFs) was investigated to gain an understanding of the mechanisms and key pathways of HL. The association between TFs and miRNAs, miRNAs and target genes and miRNA and its host gene was examined. To show the regulatory correlation clearly, three regulatory networks were hierarchically constructed: Differentially expressed, associated and global networks. Following comparison and analysis of the similarities and differences among the three networks, a number of key pathways, which showed self-adaptation associations were identified. This included NFκB1 and hsa-miR-9, hsa-miR-196a-1 and its host gene HOXB7, which separately forms a self-adaptation association. The differentially expressed network illuminated the pathogenesis of HL. In addition, the associated network further described the regulatory mechanism associated with HL, including prevention, diagnosis, development and therapy. The current study systematically explains the regulatory mechanisms of HL and supplies comprehensive data associated with HL for further studies. With increasing knowledge of the occurrence, mechanism, improvement, metastasis and treatment, an increased understanding of HL may be achieved.

p53 protein expression in chronic lymphocytic leukemia

Alterations in the function of the p53 pathway are frequently described in chronic lymphocytic leukemia (CLL), mostly associated with deletion of 17p13 and/or mutations of the TP53 gene. In the present study, we investigated 103 CLLs for the impact of protein expression of full-length p53 and its isoforms β and γ. A strong correlation between deletions of 17p13 and an accumulation of full-length p53 protein was found and was associated with a worse outcome compared to CLL with normal p53 (treatment-free survival p < 0.001, overall survival p = 0.04). Interestingly, the relative expression levels between full-length p53 protein and its isoforms β and γ were significantly altered in CLL even without deletions of 17p13, compared to normal B-cells (p = 0.005). Furthermore, CLLs with higher p53 protein ratios showed worse clinical courses compared to CLLs with lower p53 protein ratios. Taken together, the differential expression of p53 isoforms could disrupt the p53 response and contribute to CLL pathogenesis.

Hodgkin lymphoma risk: role of genetic polymorphisms and gene-gene interactions in DNA repair pathways

DNA repair variants may play a potentially important role in an individual's susceptibility to developing cancer. Numerous studies have reported the association between genetic single nucleotide polymorphisms (SNPs) in DNA repair genes and different types of hematologic cancers. However, to date, the effects of such SNPs on modulating Hodgkin lymphoma (HL) risk have not yet been investigated. We hypothesized that gene-gene interaction between candidate genes in direct reversal, nucleotide excision repair (NER), base excision repair (BER) and double strand break (DSB) pathways may contribute to susceptibility to HL. To test this hypothesis, we conducted a study on 200 HL cases and 220 controls to assess associations between HL risk and 21 functional SNPs in DNA repair genes. We evaluated potential gene-gene interactions and the association of multiple polymorphisms in a chromosome region using a multi-analytic strategy combining logistic regression, multi-factor dimensionality reduction and classification and regression tree approaches. We observed that, in combination, allelic variants in the XPC Ala499Val, NBN Glu185Gln, XRCC3 Thr241Me, XRCC1 Arg194Trp, and XRCC1 399Gln polymorphisms modify the risk for developing HL. Moreover, the cumulative genetic risk score revealed a significant trend where the risk for developing HL increases as the number of adverse alleles in BER and DSB genes increase. These findings suggest that DNA repair variants in BER and DSB pathways may play an important role in the development of HL.

EBV-positive Hodgkin lymphoma is associated with suppression of p21cip1/waf1 and a worse prognosis

BACKGROUND

About 30-50% of Hodgkin lymphomas (HLs) harbor the Epstein-Barr virus (EBV), but the impact of EBV infection on clinical outcomes has been unclear. EBV-encoded small RNAs (EBERs) are presented in all EBV-infected cells, but their functions are still less understood.

RESULTS

EBER1 was transfected into two HL cell lines, KMH2 and L428, and microarrays were used to screen for EBER1-induced changes. We found that EBER1 suppressed p21cip1/waf1 transcription in HL cell lines. In addition, positive regulators of p21cip1/waf1 transcription, such as p53, EGR1, and STAT1, were decreased. Suppression of p21cip1/waf1 in the EBER1+ HL cell lines was associated with increased resistance to histone deacetylase inhibitors or proteasome inhibitors, drugs known to cause apoptosis by increasing p21cip1/waf1 levels. On biopsy specimens, EBV+ HLs had weaker expression of both p21cip1/waf1 and active caspase 3. Clinically, suppression of p21cip1/waf1 in EBV+ HLs was associated with a worse 2-year disease-free survival rate (45% for EBV+ HLs vs. 77% for EBV- HLs, p = 0.002).

CONCLUSION

Although the underlying mechanisms are still relatively unclear, EBER1 inhibits p21cip1/waf1 transcription and prevents apoptosis through down-regulation of p53, EGR1, and STAT1. The anti-apoptotic activity of EBER1 may be important in the rescue of Reed-Sternberg cells from drug-induced apoptosis and in the clinical behaviors of EBV+ HLs.

Hodgkin lymphoma: an update on its biology with new insights into classification

In the past few years, there has been a greater understanding of the spectrum and biology of Hodgkin lymphoma (HL). In standard texts, HL is classified as 2 distinct entities, namely nodular lymphocyte-predominant HL and classical HL (CHL). However, recent evidence suggests that CHL is not a single disease. Although the mixed cellularity and lymphocyte-depleted subtypes might be part of a biologic continuum, the nodular sclerosis subtype has a distinct epidemiology, clinical presentation, and histology. Nodular sclerosis HL might also be related to primary mediastinal B-cell lymphoma and mediastinal gray-zone lymphomas. We present an update on the pathobiology of HL and discuss these biologic and clinical differences in this review.

Genetic polymorphisms in DNA repair genes as modulators of Hodgkin disease risk

BACKGROUND

Although the pathogenesis of Hodgkin disease (HD) remains unknown, the results of epidemiologic studies suggest that heritable factors are important in terms of susceptibility. Polymorphisms in DNA repair genes may contribute to individual susceptibility for development of different cancers. However, to the authors' knowledge, few studies to date have investigated the role of such polymorphisms as risk factors for development of HD.

METHODS

The authors evaluated the relation between polymorphisms in 3 nucleotide excision repair pathway genes (XPD [Lys751Gln], XPC [Lys939Gln], and XPG [Asp1104His]), the base excision repair XRCC1 (Arg399Gln), and double-strand break repair XRCC3 (Thr241Met) in a population of 200 HD cases and 220 matched controls. Variants were investigated independently and in combination; odd ratios (OR) were calculated.

RESULTS

A positive association was found for XRCC1 gene polymorphism Arg399Gln (OR, 1.77; 95% confidence interval [95% CI], 1.16-2.71) and risk of HD. The combined analysis demonstrated that XRCC1/XRCC3 and XRCC1/XPC polymorphisms were associated with a significant increase in HD risk. XRCC1 Arg/Arg and XRCC3 Thr/Met genotypes combined were associated with an OR of 2.38 (95% CI, 1.24-4.55). The XRCC1 Arg/Gln and XRCC3 Thr/Thr, Thr/Met, and Met/Met genotypes had ORs of 1.88 (95% CI, 1.02-4.10), 1.97 (95% CI, 1.05-3.73), and 4.13 (95% CI, 1.50-11.33), respectively. XRCC1 Gln/Gln and XRCC3 Thr/Thr variant led to a significant increase in risk, with ORs of 3.00 (95% CI, 1.15-7.80). Similarly, XRCC1 Arg/Gln together with XPC Lys/Lys was found to significantly increase the risk of HD (OR, 2.14; 95% CI, 1.09-4.23).

CONCLUSIONS

These data suggest that genetic polymorphisms in DNA repair genes may modify the risk of HD, especially when interactions between the pathways are considered.

Pathogenesis of classical and lymphocyte-predominant Hodgkin lymphoma

Hodgkin and Reed-Sternberg (HRS) cells in classical Hodgkin lymphoma (HL) and lymphocytic and histiocytic (L&H) cells in nodular lymphocyte-predominant HL (NLPHL) are derived from germinal-center B cells. HRS cells have, however, largely lost their B cell phenotype and aberrantly express markers and transcriptional regulators of other hematolymphoid cell types. Deregulation of multiple signaling pathways and downstream transcription factors, including receptor tyrosine kinases, nuclear factor-kappa B (NF-kappaB), and Janus kinase/signal transducer and activator of transcription (JAK/STAT), is a further hallmark of HRS cells. These cells harbor genetic lesions that contribute to or cause increases in the activity of transcription factors of the NF-kappaB and STAT families. HRS cells are found within a mixed reactive cellular infiltrate and interact with these nonmalignant cells in a complex fashion that appears to be essential for HRS cell survival and proliferation. Less is known about the pathogenesis of L&H cells in NLPHL, but increases in the activity of receptor tyrosine kinases, NF-kappaB, and JAK/STAT have also been detected.

The biology of Hodgkin's lymphoma

Hodgkin's lymphoma was first described in 1832. The aetiology of this lymphoma, however, remained enigmatic for a long time. Only within the past 10 years has the B-cell nature of the pathognomonic Hodgkin and Reed-Sternberg (HRS) cells been revealed, along with several recurrent genetic lesions. The pathogenetic role for Epstein-Barr virus infection has also been substantiated. HRS cells in classical Hodgkin's lymphoma have several characteristics that are unusual for lymphoid tumour cells, and the Hodgkin's lymphoma microenvironment is dominated by an extensive mixed, potentially inflammatory cellular infiltrate. Understanding the contribution of all of these changes to the pathogenesis of this disease is essential for the development of novel therapies.

Identification of candidate tumour suppressor gene loci for Hodgkin and Reed-Sternberg cells by characterisation of homozygous deletions in classical Hodgkin lymphoma cell lines

Several tumour suppressor genes (TSG) have been identified as a result of mapping homozygous deletions in cancer cells. To identify putative TSG involved in the pathogenesis of classical Hodgkin lymphoma (cHL), we investigated four cHL cell lines (L428, HDLM2, KMH2, L1236) using four different array-Comparative Genomic Hybridisation (array-CGH) platforms and focused on high resolution identification of homozygous deletions. Out of 79 candidate regions of bi-allelic loss identified by array-CGH, besides previously described regions, 28 novel regions of homozygous deletions could be verified by polymerase chain reaction. These regions ranged from 13 kb to 619 kb in size. Eleven of the 28 novel bi-allelic losses were putative copy number polymorphisms. This left 17 regions that might harbour novel tumour suppressors involved in Hodgkin lymphoma. Expression profiling with two different platforms confirmed lack of expression of the majority of the genes located in the homozygous deletions. Furthermore, analysis of ontology annotations of genes located in the homozygously deleted regions indicated an enrichment of genes involved in apoptosis and cell death. In summary, through the mapping of homozygous deletions in cell lines this study identified a series of genes, such as SEPT9, GNG7 and CYBB, which might encode candidate tumour suppressors involved in the pathogenesis of cHL.