c-Myc oncogene and Cdc25A cell activating phosphatase expression in non-Hodgkin's lymphoma

Normal and Neoplastic Growth Suppression by the Extended Myc Network

Among the first discovered and most prominent cellular oncogenes is MYC, which encodes a bHLH-ZIP transcription factor (Myc) that both activates and suppresses numerous genes involved in proliferation, energy production, metabolism and translation. Myc belongs to a small group of bHLH-ZIP transcriptional regulators (the Myc Network) that includes its obligate heterodimerization partner Max and six "Mxd proteins" (Mxd1-4, Mnt and Mga), each of which heterodimerizes with Max and largely opposes Myc's functions. More recently, a second group of bHLH-ZIP proteins (the Mlx Network) has emerged that bears many parallels with the Myc Network. It is comprised of the Myc-like factors ChREBP and MondoA, which, in association with the Max-like member Mlx, regulate smaller and more functionally restricted repertoires of target genes, some of which are shared with Myc. Opposing ChREBP and MondoA are heterodimers comprised of Mlx and Mxd1, Mxd4 and Mnt, which also structurally and operationally link the two Networks. We discuss here the functions of these "Extended Myc Network" members, with particular emphasis on their roles in suppressing normal and neoplastic growth. These roles are complex due to the temporal- and tissue-restricted expression of Extended Myc Network proteins in normal cells, their regulation of both common and unique target genes and, in some cases, their functional redundancy.

Efficacy of pH-Sensitive Nanomedicines in Tumors with Different c-MYC Expression Depends on the Intratumoral Activation Profile

Effective inhibition of the protein derived from cellular myelocytomatosis oncogene (c-Myc) is one of the most sought-after goals in cancer therapy. While several c-Myc inhibitors have demonstrated therapeutic potential, inhibiting c-Myc has proven challenging, since c-Myc is essential for normal tissues and tumors may present heterogeneous c-Myc levels demanding contrasting therapeutic strategies. Herein, we developed tumor-targeted nanomedicines capable of treating both tumors with high and low c-Myc levels by adjusting their ability to spatiotemporally control drug action. These nanomedicines loaded homologues of the bromodomain and extraterminal (BET) motif inhibitor JQ1 as epigenetic c-Myc inhibitors through pH-cleavable bonds engineered for fast or slow drug release at intratumoral pH. In tumors with high c-Myc expression, the fast-releasing (FR) nanomedicines suppressed tumor growth more effectively than the slow-releasing (SR) ones, whereas, in the low c-Myc tumors, the efficacy of the nanomedicines was the opposite. By studying the tumor distribution and intratumoral activation of the nanomedicines, we found that, despite SR nanomedicines achieved higher accumulation than the FR counterparts in both c-Myc high and low tumors, the antitumor activity profiles corresponded with the availability of activated drugs inside the tumors. These results indicate the potential of engineered nanomedicines for c-Myc inhibition and spur the idea of precision pH-sensitive nanomedicine based on cancer biomarker levels.

Effects of let-7c on the proliferation of ovarian carcinoma cells by targeted regulation of CDC25a gene expression

MicroRNAs serve a role in the development of ovarian cancer (OC). The present study investigated whether let-7c is able to regulate the proliferation of OC cells by targeting cell division cycle 25A (CDC25a). The reverse transcription-quantitative polymerase chain reaction was performed to detect the expression of let-7c in OC specimens. Let-7c agomir was transfected into OC cells, and the proliferation and apoptosis of OC cells were detected. A dual-luciferase assay and western blotting were performed to analyze whether CDC25a was the target gene of let-7c as well as its interaction site. The results revealed that, in OC tissue, let-7c was downregulated when compared with normal ovarian tissue. A Cell Counting Kit-8 (CCK8) assay, colony formation assay and flow cytometry demonstrated that increased expression of let-7c was able to inhibit the proliferation and increase the apoptosis of OC cells. Western blotting revealed that upregulated let-7c is able to decrease the expression of CDC25a, and a dual-luciferase assay and a recovery assay demonstrated that let-7c was able to regulate the expression of the 3' untranslated region of CDC25a. Therefore, the roles of let-7c in inhibiting the proliferation and promoting the apoptosis of OC cells may be realized through the regulation of the expression of CDC25a. The results of the present study revealed that let-7c may be a novel target in the diagnosis and treatment of OC.

Association of CDC25 phosphatase family polymorphisms with the efficacy/toxicity of platinum-based chemotherapy in Chinese advanced NSCLC patients

AIM

To explore relationships between single nucleotide polymorphisms (SNPs) of the CDC25 protein family and the survival and chemotherapy responses of patients with advanced non-small-cell lung cancer (NSCLC).

METHODS & MATERIALS

We genotyped 14 SNPs of the CDC25 family in 663 Chinese patients with advanced NSCLC who were treated with first-line platinum-based chemotherapy and, in evaluable patients, analyzed relationships between the CDC25 family and the efficacy of platinum-based chemotherapy.

RESULTS

CDC25A rs3731513 and rs1380053, CDC25C rs6861656, CDC25A haplotype T/A/A/A/C and CDC25C haplotype A/G/G/G/C were significantly associated with the patients' progression-free survival. In addition, CDC25B rs3761218 and haplotype G/T/G/G were associated with the occurrence of severe toxicity with platinum-based chemotherapy, especially gastrointestinal and hematological toxicity.

CONCLUSION

These findings reveal a relationship between genetic variations of the CDC25 family and the efficacy and toxicity of platinum-based chemotherapy in patients with advanced NSCLC, especially in those with non-squamous-cell carcinoma.

High expression of Cdc25B and low expression of 14-3-3σ is associated with the development and poor prognosis in urothelial carcinoma of bladder

Cdc25 dual-specicity phosphatases are essential regulators at critical stages of cell cycle. Cdc25B is overexpressed in several human tumor types. The activity of Cdc25B is regulated by 14-3-3 dimer. To investigate the roles of Cdc25B and 14-3-3σ in bladder carcinoma, we examined expressions of Cdc25B and 14-3-3σ proteins in bladder carcinoma and cell lines and analyzed their roles in the development and prognosis of urinary bladder carcinoma. Immunohistochmistry was used to detect the expressions of Cdc25B and 14-3-3σ in 105 bladder carcinomas. Moreover, expressions of Cdc25B and 14-3-3σ were analyzed by real-time PCR and Western blot in 40 bladder carcinomas and 20 normal epithelial tissues. Specific siRNA was used to knockdown the expression of Cdc25B or 14-3-3σ. Wild-type plasmid was used to overexpress 14-3-3σ. MTT assay and Flow cytometry were used to examine proliferation and cell cycle of bladder cancer cells. There were higher Cdc25B expression and lower 14-3-3σ expression in carcinomas than in the adjacent normal tissues (P < 0.05), positive and negative correlations being noted with clinical stage and histopathologic grade. Cdc25B expression was positively correlated with recurrence and poor prognosis. Downregulation of Cdc25B resulted in slower growth, more G2/M cells and 14-3-3σ increasing. However, upregulation and downregulation of 14-3-3σ did not affect cell growth and Cdc25B expression. It showed that Cdc25B upregulation and 14-3-3σ downregulation might promote development of bladder cancer and suggested a poor prognosis. Moreover, Cdc25B could play an important role on the bladder cancer cell proliferation and cell cycle progression and regulate expression of 14-3-3σ.

High-resolution genomic profiling of chronic lymphocytic leukemia reveals new recurrent genomic alterations

To identify genomic alterations in chronic lymphocytic leukemia (CLL), we performed single-nucleotide polymorphism–array analysis using Affymetrix Version 6.0 on 353 samples from untreated patients entered in the CLL8 treatment trial. Based on paired-sample analysis (n = 144), a mean of 1.8 copy number alterations per patient were identified; approximately 60% of patients carried no copy number alterations other than those detected by fluorescence in situ hybridization analysis. Copy-neutral loss-of-heterozygosity was detected in 6% of CLL patients and was found most frequently on 13q, 17p, and 11q. Minimally deleted regions were refined on 13q14 (deleted in 61% of patients) to the DLEU1 and DLEU2 genes, on 11q22.3 (27% of patients) to ATM, on 2p16.1-2p15 (gained in 7% of patients) to a 1.9-Mb fragment containing 9 genes, and on 8q24.21 (5% of patients) to a segment 486 kb proximal to the MYC locus. 13q deletions exhibited proximal and distal breakpoint cluster regions. Among the most common novel lesions were deletions at 15q15.1 (4% of patients), with the smallest deletion (70.48 kb) found in the MGA locus. Sequence analysis of MGA in 59 samples revealed a truncating mutation in one CLL patient lacking a 15q deletion. MNT at 17p13.3, which in addition to MGA and MYC encodes for the network of MAX-interacting proteins, was also deleted recurrently.

Bcl-6 and c-Myc are rarely co-expressed in adult diffuse large B-cell lymphoma

Bcl-6 is expressed in germinal centre derived B-cell non-Hodgkin lymphomas including diffuse large B-cell lymphoma (DLBCL) and is likely to play a major role in driving proliferation of a subset of DLBCLs, especially those of germinal centre B-cell subtype, but the role of c-Myc, which is important for proliferation in various lineages is not known. We used the highly standardised staining conditions of a tissue microarray to characterise co-expression of c-Myc and Bcl-6 in DLBCL. We carried out immunohistochemistry of 73 arrayed cases. The majority (62/73) did not express c-Myc, but 11 cases (15%) showed nuclear staining. 5/53 (9%) of Bcl-6 expressing cases co-expressed c-Myc, whereas a much higher proportion, 6/20 (30%), of Bcl-6 negative cases were positive for c-Myc. Overall survival of c-Myc expressing cases was the same as those that had absent expression. There was no significant correlation between c-Myc expression and DLBCL subtype (germinal centre or non-germinal centre subtypes).

Cyclin Dl expression in B-cell non Hodgkin lymphoma

Disorders of the cell cycle regulatory machinery play a key role in the pathogenesis of cancer. Over-expression of cyclin D1 protein has been reported in several solid tumors and certain lymphoid malignancies, but little is known about the effect of its expression on clinical behavior and outcome in B-cell Non-Hodgkin lymphoma (NHL). In this study, we investigated the expression of cyclin Dl in group of patients with NHL and correlated the results with the clinical and laboratory data. The degree of expression of cyclin Dl protein was evaluated by flow cytometry in a group of NHL patients (n = 46) and in normal control group (n = 10). Cyclin Dl over expression was detected in 10 out of 46 (21.7%) patients; they were 5/5-mantle cell lymphoma (MCL) (100%) and 5/28 large B-cell lymphoma (17.8%). All other NHL subtypes showed normal cyclin D1 expression. The clinical signs (hepatomegaly, splenomegaly and B-symptoms, clinical staging) and laboratory data (hemoglobin, white cell count (WBCs), platelet count, and bone marrow infiltration) were not significantly different between NHL subgroup with cyclin Dl over expression and that with normal cyclin Dl expression. Serum lactic dehydrogenase (LDH) levels and lymphadenopathy were significantly higher in NHL group with cyclin D1 over expression as compared to those without. Also, cyclin D1 over expression is associated with poor outcome of NHL patients. Cyclin Dl over expression was evident among all cases of MCL and few cases of large B-cell lymphoma. Cyclin Dl over expression might be used as adjuvant tool for diagnosis of MCL; has role in NHL biology and is bad prognostic index in NHL.

CDC25 phosphatases in cancer cells: key players? Good targets?

Cell division cycle 25 (CDC25) phosphatases regulate key transitions between cell cycle phases during normal cell division, and in the event of DNA damage they are key targets of the checkpoint machinery that ensures genetic stability. Taking only this into consideration, it is not surprising that CDC25 overexpression has been reported in a significant number of human cancers. However, in light of the significant body of evidence detailing the stringent complexity with which CDC25 activities are regulated, the significance of CDC25 overexpression in a subset of cancers and its association with poor prognosis are proving difficult to assess. We will focus on the roles of CDC25 phosphatases in both normal and abnormal cell proliferation, provide a critical assessment of the current data on CDC25 overexpression in cancer, and discuss both current and future therapeutic strategies for targeting CDC25 activity in cancer treatment.

DUAL SPECIFICITY PROTEIN PHOSPHATASES: Therapeutic Targets for Cancer and Alzheimer's Disease

The complete sequencing of the human genome is generating many novel targets for drug discovery. Understanding the pathophysiological roles of these putative targets and assessing their suitability for therapeutic intervention has become the major hurdle for drug discovery efforts. The dual-specificity phosphatases (DSPases), which dephosphorylate serine, threonine, and tyrosine residues in the same protein substrate, have important roles in multiple signaling pathways and appear to be deregulated in cancer and Alzheimer's disease. We examine the potential of DSPases as new molecular therapeutic targets for the treatment of human disease.

Evidence for distinct pathomechanisms in genetic subgroups of chronic lymphocytic leukemia revealed by quantitative expression analysis of cell cycle, activation, and apoptosis-associated genes

PURPOSE

In patients with chronic lymphocytic leukemia (CLL), the VH mutation status and genomic aberrations (13q-, +12q, 11q-, 17p-) identify distinct prognostic subgroups. The aim was to elucidate biologic mechanisms through which these genetic markers may exert their pathogenic influence.

PATIENTS AND METHODS

Twenty-four genes involved in apoptosis, cell cycle, B-cell activation, and B-cell receptor (BCR) signaling were analyzed by real-time quantitative reverse transcription polymerase chain reaction (RQ-PCR) in 82 CLL cases constituting prototypic genetic CLL subgroups as defined by the VH mutation status and the genomic aberrations 13q-, +12, 11q-, and 17p-.

RESULTS

The VH mutation subgroups were characterized by a differential expression of the BCR associated genes ZAP70 and PI3K. Among the subgroups defined by genomic aberrations, there was a deregulation of candidate genes from the affected critical genomic regions such as CDK4 (up), ATM (down), and TP53 (down) in the groups +12, 11q-, and 17p-, respectively. Additionally, the genomic subgroups were characterized by a significant deregulation of cell cycle and apoptosis regulators: AKT (up) in 13q, E2F1 (up) in +12, MYC (up) and BCL-2 (down) in 17p-, and CCND3 (down) in 11q- as well as 17p-. The 17p- subgroup showed an additional down-regulation of BCR-associated genes such as SYK and PI3K.

CONCLUSION

The characteristic gene expression patterns observed implicate a differential regulation of cell cycle, apoptosis, and BCR signaling in the genetic subgroups illustrating distinct pathomechanisms and are evidence for a gene dosage effect being operative in CLL. These findings link the biologic diversity and clinical heterogeneity of CLL.