Role of PLZF in melanoma progression

ZBTB16 inhibits DNA replication and induces cell cycle arrest by targeting WDHD1 transcription in lung adenocarcinoma

Lung adenocarcinoma is a malignant tumor with high morbidity and mortality. ZBTB16 plays a double role in various tumors; however, the potential mechanism of ZBTB16 in the pathophysiology of lung adenocarcinoma has yet to be elucidated. We herein observed a decreased expression of ZBTB16 mRNA and protein in lung adenocarcinoma and a significantly increased DNA methylation level of ZBTB16 in patients with lung adenocarcinoma. Analysis of public databases and patients' clinical data indicated a close association between ZBTB16 and patient survival. Ectopic expression of ZBTB16 in lung adenocarcinoma cells significantly inhibited cell proliferation, invasion, and migration. It also induced cell cycle arrest in the S phase. Meanwhile, mitotic catastrophe was induced, and DNA damage and apoptosis occurred. In line with these findings, the overexpression of ZBTB16 in xenograft mice resulted in the inhibition of tumor growth. Comprehensive analysis showed that WDHD1 was a potential target for ZBTB16. The overexpression of both isoforms of WDHD1 significantly reversed the ZBTB16-mediated inhibition of lung adenocarcinoma proliferation and cell cycle. These studies suggest that ZBTB16 impedes the progression of lung adenocarcinoma by interfering with WDHD1 transcription, making it a potential novel therapeutic target in the management of lung adenocarcinoma.

Identification of Candidate Genes Regulating Carcass Depth and Hind Leg Circumference in Simmental Beef Cattle Using Illumina Bovine Beadchip and Next-Generation Sequencing Analyses

Genome-wide association studies are a robust means of identifying candidate genes that regulate economically important traits in farm animals. The aim of this study is to identify single-nucleotide polymorphisms (SNPs) and candidate genes potentially related to carcass depth and hind leg circumference in Simmental beef cattle. We performed Illumina Bovine HD Beadchip (~670 k SNPs) and next-generation sequencing (~12 million imputed SNPs) analyses of data from 1252 beef cattle, to which we applied a linear mixed model. Using a statistical threshold (p = 0.05/number of SNPs identified) and adopting a false discovery rate (FDR), we identified many putative SNPs on different bovine chromosomes. We identified 12 candidate genes potentially annotated with the markers identified, including CDKAL1 and E2F3, related to myogenesis and skeletal muscle development. The identification of such genes in Simmental beef cattle will help breeders to understand and improve related traits, such as meat yield.

Functional analysis of low-grade glioma genetic variants predicts key target genes and transcription factors

BACKGROUND

Large-scale genome-wide association studies (GWAS) have implicated thousands of germline genetic variants in modulating individuals' risk to various diseases, including cancer. At least 25 risk loci have been identified for low-grade gliomas (LGGs), but their molecular functions remain largely unknown.

METHODS

We hypothesized that GWAS loci contain causal single nucleotide polymorphisms (SNPs) that reside in accessible open chromatin regions and modulate the expression of target genes by perturbing the binding affinity of transcription factors (TFs). We performed an integrative analysis of genomic and epigenomic data from The Cancer Genome Atlas and other public repositories to identify candidate causal SNPs within linkage disequilibrium blocks of LGG GWAS loci. We assessed their potential regulatory role via in silico TF binding sequence perturbations, convolutional neural network trained on TF binding data, and simulated annealing-based interpretation methods.

RESULTS

We built an interactive website (http://education.knoweng.org/alg3/) summarizing the functional footprinting of 280 variants in 25 LGG GWAS regions, providing rich information for further computational and experimental scrutiny. We identified as case studies PHLDB1 and SLC25A26 as candidate target genes of rs12803321 and rs11706832, respectively, and predicted the GWAS variant rs648044 to be the causal SNP modulating ZBTB16, a known tumor suppressor in multiple cancers. We showed that rs648044 likely perturbed the binding affinity of the TF MAFF, as supported by RNA interference and in vitro MAFF binding experiments.

CONCLUSIONS

The identified candidate (causal SNP, target gene, TF) triplets and the accompanying resource will help accelerate our understanding of the molecular mechanisms underlying genetic risk factors for gliomas.

Transcriptional signatures underlying dynamic phenotypic switching and novel disease biomarkers in a linear cellular model of melanoma progression

Despite advances in therapeutics, the progression of melanoma to metastasis still confers a poor outcome to patients. Nevertheless, there is a scarcity of biological models to understand cellular and molecular changes taking place along disease progression. Here, we characterized the transcriptome profiles of a multi-stage murine model of melanoma progression comprising a nontumorigenic melanocyte lineage (melan-a), premalignant melanocytes (4C), nonmetastatic (4C11-) and metastasis-prone (4C11+) melanoma cells. Clustering analyses have grouped the 4 cell lines according to their differentiated (melan-a and 4C11+) or undifferentiated/"mesenchymal-like" (4C and 4C11-) morphologies, suggesting dynamic gene expression patterns associated with the transition between these phenotypes. The cell plasticity observed in the murine melanoma progression model was corroborated by molecular markers described during stepwise human melanoma differentiation, as the differentiated cell lines in our model exhibit upregulation of transitory and melanocytic markers, whereas "mesenchymal-like" cells show increased expression of undifferentiated and neural crest-like markers. Sets of differentially expressed genes (DEGs) were detected at each transition step of tumor progression, and transcriptional signatures related to malignancy, metastasis and epithelial-to-mesenchymal transition were identified. Finally, DEGs were mapped to their human orthologs and evaluated in uni- and multivariate survival analyses using gene expression and clinical data of 703 drug-naïve primary melanoma patients, revealing several independent candidate prognostic markers. Altogether, these results provide novel insights into the molecular mechanisms underlying the phenotypic switch taking place during melanoma progression, reveal potential drug targets and prognostic biomarkers, and corroborate the translational relevance of this unique sequential model of melanoma progression.

Crosstalk Between Prostate Cancer Cells and Tumor-Associated Fibroblasts Enhances the Malignancy by Inhibiting the Tumor Suppressor PLZF

Although prostate cancer is clinically manageable during the early stages of progression, metastatic progression severely compromises the prognosis and leads to mortality. Constitutive activation of STAT3 has been connected to prostate cancer malignancy, and abolishing the STAT3 activity may diminish tumor growth and metastasis. However, its suppressor genes and pathways have not been well established. In this study, we show that promyelocytic leukemia zinc finger (PLZF) has a putative tumor-suppressor function in prostate cancer by inhibiting phosphorylation of STAT3. Compared with a benign prostate, high-grade prostate cancer patient tissue was negatively correlated with PLZF expression. PLZF depletion accelerated proliferation and survival, migration, and invasion in human prostate cancer cells. Mechanistically, we demonstrated a novel role of PLZF as the transcriptional regulator of the tyrosine phosphatase SHP-1 that inhibits the oncogenic JAKs–STAT3 pathway. These results suggest that the collapse of PLZF expression by the CCL3 derived from fibroblasts accelerates the cell migration and invasion properties of prostate cancer cells. Our results suggest that increasing PLZF could be an attractive strategy for suppressing prostate cancer metastasis as well as for tumor growth.

MiR-4319 suppresses colorectal cancer progression by targeting ABTB1

Background

Colorectal cancer is one of the highly malignant cancers with a poor prognosis. The exact mechanism of colorectal cancer progression is not completely known. Recently, microRNAs (miRNAs, miRs) were suggested to participate in the regulation of multiple cancer development, including colorectal cancer.

Methods

MiR-4319 expression in colorectal cancer patient samples was detected by real-time polymerase chain reaction. MiR-4319 was knocked down in the colorectal cancer cells by siRNA transfection to study the role of miR-4319 in the cell cycle and proliferation of colorectal cancer cells.

Results

MiR-4319 expression was found to be inverse correlated with survival in colorectal cancer patients. Overexpression of miR-4319 markedly reduced the proliferation of colorectal cancer cells and altered cell cycle distribution. A further experiment showed that ABTB1 is the target gene of miR-4319. MiR-4319 was regulated by PLZF.

Conclusion

Our studies indicated that reduced expression of miR-4319 was correlated with poor prognosis in colorectal cancer patients; miR-4319 also suppressed colorectal cancer cell proliferation by targeting ABTB1. ABTB1 might become an excellent therapeutic target for colorectal cancer treatment.

PLZF inhibits proliferation and metastasis of gallbladder cancer by regulating IFIT2

Gallbladder cancer (GBC) is a malignant cancer with very poor prognosis. Although promyelocytic leukemia zinc-finger protein (PLZF) was reported to be deregulated in numerous cancers and also relevant to clinical prognosis, its role in GBC progression has been little known. In this study, we found PLZF expression was decreased in GBC, correlating to advanced TNM stage, distant metastasis, and shorter overall survival. Moreover, ectopic PLZF expression in GBC cells (NOZ and GBC-SD) significantly reduced the cell proliferation, migration, and invasion. Consistently, overexpression of PLZF in xenograft mice model could suppress tumor growth and liver metastasis. Mechanical investigations verified PLZF could regulate the expression of cell cycle arrest-associated gene p21 and epithelial–mesenchymal transition (EMT)-related genes (E-cadherin and N-cadherin) in GBC cell lines. Importantly, PLZF remarkably increased the mRNA transcription of interferon-induced protein with tetratricopeptide repeat 2 (IFIT2) by increasing STAT1 protein level, a known factor involved in tumor progression. Furthermore, ablation of IFIT2 in PLZF overexpression cells abrogated the tumor-suppressive function of PLZF, at least partially, leading to impaired tumor growth and EMT program. These studies indicated PLZF inhibited the proliferation and metastasis via regulation of IFIT2. In conclusion, our study demonstrated PLZF could be a promising tumor biomarker for GBC, and also be a potential therapeutic target.

Role of PLZF as a tumor suppressor in prostate cancer

The promyelocytic leukemia zinc finger (PLZF), also known as ZBTB16 (Zinc Finger And BTB Domain Containing 16), is a transcription factor involved in the regulation of diverse biological processes, including cell proliferation, differentiation, organ development, stem cell maintenance and innate immune cell development. A number of recent studies have now implicated PLZF in cancer progression as a tumor suppressor. However, in certain cancer types, PLZF may function as an oncoprotein. Here, we summarize our current knowledge on the role of PLZF in various cancer types, in particular prostate cancer, including its deregulation, genomic alterations and potential functions in prostate cancer progression.

AP2α controls the dynamic balance between miR-126&126* and miR-221&222 during melanoma progression

Accumulating evidences have shown the association between aberrantly expressed microRNAs (miRs) and cancer, where these small regulatory RNAs appear to dictate the cell fate by regulating all the main biological processes. We demonstrated the responsibility of the circuitry connecting the oncomiR-221&222 with the tumor suppressors miR-126&126* in melanoma development and progression. According to the inverse correlation between endogenous miR-221&222 and miR-126&126*, respectively increasing or decreasing with malignancy, their enforced expression or silencing was sufficient for a reciprocal regulation. In line with the opposite roles of these miRs, protein analyses confirmed the reverse expression pattern of miR-126&126*-targeted genes that were induced by miR-221&222. Looking for a central player in this complex network, we revealed the dual regulation of AP2α, on one side directly targeted by miR-221&222 and on the other a transcriptional activator of miR-126&126*. We showed the chance of restoring miR-126&126* expression in metastatic melanoma to reduce the amount of mature intracellular heparin-binding EGF like growth factor, thus preventing promyelocytic leukemia zinc finger delocalization and maintaining its repression on miR-221&222 promoter. Thus, the low-residual quantity of these two miRs assures the release of AP2α expression, which in turn binds to and induces miR-126&126* transcription. All together these results point to an unbalanced ratio functional to melanoma malignancy between these two couples of miRs. During progression this balance gradually moves from miR-126&126* toward miR-221&222. This circuitry, besides confirming the central role of AP2α in orchestrating melanoma development and/or progression, further displays the significance of these miRs in cancer and the option of utilizing them for novel therapeutics.

Control of hepatic gluconeogenesis by the promyelocytic leukemia zinc finger protein

The promyelocytic leukemia zinc finger (PLZF) protein is involved in major biological processes including energy metabolism, although its role remains unknown. In this study, we demonstrated that hepatic PLZF expression was induced in fasted or diabetic mice. PLZF promoted gluconeogenic gene expression and hepatic glucose output, leading to hyperglycemia. In contrast, hepatic PLZF knockdown improved glucose homeostasis in db/db mice. Mechanistically, peroxisome proliferator-activated receptor γ coactivator 1α and the glucocorticoid receptor synergistically activated PLZF expression. We conclude that PLZF is a critical regulator of hepatic gluconeogenesis. PLZF manipulation may benefit the treatment of metabolic diseases associated with gluconeogenesis.

Implication of intracellular localization of transcriptional repressor PLZF in thyroid neoplasms

BACKGROUND

Promyelocytic leukaemia zinc finger (PLZF) is a transcriptional repressor that was originally isolated from a patient with promyelocytic leukaemia. PLZF also affects key elements for cell cycle progression, such as cyclin A, and can affect the tumourigenicity of various cancers. Thus far, the behaviour of PLZF in thyroid carcinoma remains unclear.

METHODS

We analysed the expression profile of PLZF in different types of benign and malignant thyroid lesions as well as in normal thyroid tissue. Specifically, we examined PLZF expression in normal thyroid (N; n = 4), adenomatous lesion (AL; n = 5), follicular adenoma (FA; n = 2), papillary thyroid carcinoma (PTC; n = 20), and anaplastic thyroid carcinoma (ATC; n = 3) samples. PLZF expression was estimated by western blotting and immunohistochemical (IHC) staining.

RESULTS

PLZF was expressed in all samples of thyroid lesions examined. In N, AL, and FA, PLZF was mainly localized in the nucleus. In contrast, in PTC and ATC, PLZF was mainly expressed in the cytosol with high intensity. In more detail, the cytoplasmic IHC scores in PTC with capsular invasion (CI) and lymph node (LN) metastasis were higher than those in PTC without CI and LN metastasis.

CONCLUSIONS

PLZF shows different subcellular localizations among PTC, ATC, and other thyroid lesions. Furthermore, high cytoplasmic expression of PLZF may be correlated with CI and LN metastasis in thyroid carcinoma. The present report is the first to describe the implications of intracellular PLZF expression in thyroid carcinomas.

Role of promyelocytic leukemia zinc finger (PLZF) in cell proliferation and cyclin-dependent kinase inhibitor 1A (p21WAF/CDKN1A) gene repression

Promyelocytic leukemia zinc finger (PLZF) is a transcription repressor that was initially isolated as a fusion protein with retinoic acid receptor α. PLZF is aberrantly overexpressed in various human solid tumors, such as clear cell renal carcinoma, glioblastoma, and seminoma. PLZF causes cellular transformation of NIH3T3 cells and increases cell proliferation in several cell types. PLZF also increases tumor growth in the mouse xenograft tumor model. PLZF may stimulate cell proliferation by controlling expression of the genes of the p53 pathway (ARF, TP53, and CDKN1A). We found that PLZF can directly repress transcription of CDKN1A encoding p21, a negative regulator of cell cycle progression. PLZF binds to the proximal Sp1-binding GC-box 5/6 and the distal p53-responsive elements of the CDKN1A promoter to repress transcription. Interestingly, PLZF interacts with Sp1 or p53 and competes with Sp1 or p53. PLZF interacts with corepressors, such as mSin3A, NCoR, and SMRT, thereby deacetylates Ac-H3 and Ac-H4 histones at the CDKN1A promoter, which indicated the involvement of the corepressor·HDACs complex in transcription repression by PLZF. Also, PLZF represses transcription of TP53 and also decreases p53 protein stability by ubiquitination. PLZF may act as a potential proto-oncoprotein in various cell types.

Immunohistochemical detection of promyelocytic leukemia zinc finger and histone 1.5 in uterine leiomyosarcoma and leiomyoma

OBJECTIVES

The accurate distinction of leiomyoma from leiomyosarcoma is essential for patient management. However, the distinction can be difficult to make, particularly in tissue biopsy samples. Immunohistochemistry has been established as a useful technique to aid in the diagnosis of malignancies. The advantages of immunohistochemical studies are their ease of use and interpretation. This study is the first to evaluate the utility of the promyelocytic leukemia zinc finger (PLZF) protein and the histone 1.5 (H1.5) protein as potential diagnostic immunohistochemical markers for distinguishing leiomyosarcoma from leiomyoma.

METHODS

Tissue samples from 21 leiomyosarcomas and 26 leiomyomas were studied. The student t-test and the Fisher exact test were used to calculate the differences in staining between the 2 groups.

RESULTS

Statistically significant differences were found in the staining indices of anti-PLZF and anti-H1.5 when comparing benign and malignant tumors (P < .0001 and P < .0001, respectively). The mean H1.5 staining score in leiomyosarcomas was 158.3, compared to 28.3 in leiomyomas. The mean PLZF score in leiomyosarcomas was 1.5 in contrast to 71.5 in leiomyomas. For H1.5 at a score ≥60, the sensitivity and specificity were 90.5% and 84.6%, respectively. For PLZF, a score ≤15 had a test sensitivity and specificity of 100% and 80.8%, respectively. This suggests that staining for H1.5 or PLZF can serve as a good screening test. Additionally, combining the 2 immunostains results in a sensitivity and specificity of 90.5% and 97.5%, respectively, in differentiating between leiomyoma and leiomyosarcoma.

CONCLUSIONS

We describe immunostaining for PLZF and H1.5 in benign and malignant uterine smooth muscle tumors. Statistically significant differences in staining patterns were found, suggesting utility in distinguishing leiomyosarcomas from leiomyomas.

HOXB1 restored expression promotes apoptosis and differentiation in the HL60 leukemic cell line

BACKGROUND

Homeobox (HOX) genes deregulation has been largely implicated in the development of human leukemia. Among the HOXB cluster, HOXB1 was silent in a number of analyzed acute myeloid leukemia (AML) primary cells and cell lines, whereas it was expressed in normal terminally differentiated peripheral blood cells.

METHODS

We evaluated the biological effects and the transcriptome changes determined by the retroviral transduction of HOXB1 in the human promyelocytic cell line HL60.

RESULTS

Our results suggest that the enforced expression of HOXB1 reduces cell growth proliferation, inducing apoptosis and cell differentiation along the monocytic and granulocytic lineages. Accordingly, gene expression analysis showed the HOXB1-dependent down-regulation of some tumor promoting genes, paralleled by the up-regulation of apoptosis- and differentiation-related genes, thus supporting a tumor suppressor role for HOXB1 in AML. Finally, we indicated HOXB1 promoter hypermethylation as a mechanism responsible for HOXB1 silencing.

CONCLUSIONS

We propose HOXB1 as an additional member of the HOX family with tumour suppressor properties suggesting a HOXB1/ATRA combination as a possible future therapeutic strategy in AML.

The abrogation of the HOXB7/PBX2 complex induces apoptosis in melanoma through the miR-221&222-c-FOS pathway

Cutaneous melanoma is the fastest increasing cancer worldwide. Although several molecular abnormalities have been associated with melanoma progression, the underlying mechanisms are still largely unknown and few targeted therapies are under evaluation. Here we show that the HOXB7/PBX2 dimer acts as a positive transcriptional regulator of the oncogenic microRNA-221 and -222. In addition, demonstrating c-FOS as a direct target of miR-221&222, we identify a HOXB7/PBX2→miR-221&222 →c-FOS regulatory link, whereby the abrogation of functional HOXB7/PBX2 dimers leads to reduced miR-221&222 transcription and elevated c-FOS expression with consequent cell death. Taking advantage of the treatment with the peptide HXR9, an antagonist of HOX/PBX dimerization, we recognize miR-221&222 as effectors of its action, in turn confirming the HXR9 efficacy in the treatment of human melanoma malignancy, whilst sparing normal human melanocytes. Our findings, besides suggesting the potential therapeutic of HXR9 or its derivatives in malignant melanoma, suggest the disruption of the HOXB7/PBX2 complexes, miR-221&222 inhibition or even better their combination, as innovative therapeutic approaches.

Promyelocytic leukemia zinc finger and histone H1.5 differentially stain low- and high-grade pulmonary neuroendocrine tumors: a pilot immunohistochemical study

Promyelocytic leukemia zinc finger is a zinc finger transcription factor that functions as a transcriptional repressor. Its expression has been shown to be down-regulated in hematopoietic, melanocytic, and mesothelial malignancies. Histone H1.5 is a variant of histone H1, a family of linker proteins that organizes chromosomes into higher order structures. Its function is of key importance in gene expression and has been linked to more aggressive forms of prostatic carcinoma. This study aimed to investigate the immunohistochemical detectability of promyelocytic leukemia zinc finger and histone H1.5 in pulmonary neuroendocrine tumors, comprising 11 carcinoid tumorlets, 24 typical carcinoids, 12 atypical carcinoids, 20 small cell carcinomas, 11 large cell neuroendocrine carcinomas, and 2 combined small cell carcinomas-large cell neuroendocrine carcinomas. Promyelocytic leukemia zinc finger immunohistochemistry revealed moderate or strong nuclear staining in all carcinoid tumorlets, 23 of 24 typical carcinoids, and 7 of 12 atypical carcinoids in contrast to 9 of 11 large cell neuroendocrine carcinomas, all small cell carcinoma, and both combined small cell carcinoma-large cell neuroendocrine carcinomas, which showed no nuclear immunoreactivity. Histone H1.5 immunohistochemistry revealed only focal or no immunoreactivity in all carcinoid tumorlets and 19 of 24 typical carcinoids, whereas 7 of 12 atypical carcinoids, 19 of 20 small cell carcinomas, 10 of 11 large cell neuroendocrine carcinomas, and both combined small cell carcinomas-large cell neuroendocrine carcinomas displayed positive (≥ 10%) nuclear immunoreactivity-ranging from a minority of weak staining to a majority of strong staining cases. Our data suggest that the relative expression ratios of promyelocytic leukemia zinc finger and histone H1.5 may correlate with grade of pulmonary neuroendocrine tumors. Immunohistochemical stains for these markers, especially on small biopsies with crush artifact, may prove to be diagnostically useful.

Identification of a novel promyelocytic leukemia zinc-finger isoform required for colorectal cancer cell growth and survival

Promyelocytic leukemia zinc-finger (PLZF) is a transcriptional repressor that regulates proliferation, differentiation and apoptosis among various cellular origins. PLZF expression is upregulated in colorectal cancer cell lines but its putative functional role in this context is unknown. Here, we report the identification of a novel p65 PLZF isoform that results from the usage of an evolutionarily conserved alternative translational initiation site. This isoform is devoid of the classical BTB/POZ domain required for nuclear localization and transcriptional repression. Depletion of p65 PLZF expression in colorectal cancer cell lines results in reduction of cell growth, loss of cell anchorage and increase in cell apoptosis. Overall, these results indicate that p65 PLZF is crucial to maintain colorectal cancer cell adhesion as well as survival and must occur independently of the traditionally viewed transcriptional role of PLZF in the course of these biological processes.

HOX Gene Aberrant Expression in Skin Melanoma: A Review

The homeobox family and its subset of HOX gene products represent a family of transcription factors directing DNA-protein and protein-protein interactions. In the embryo, they are central regulators in cell differentiation during morphogenesis. A series of genes of the four HOX gene clusters A, B, C, and D were reported to show aberrant expressions in oncogenesis, particularly in cutaneous malignant melanoma (CMM). They are involved in cell proliferation and progression in the CMM metastatic path. We present relevant peer-reviewed literature findings about the aberrant expression of HOX genes in CMM. The number of CMM cell nuclei exhibiting aberrant HOX protein expression appears correlated with tumour progression.

The miR-200 and miR-221/222 microRNA families: opposing effects on epithelial identity

Carcinogenesis is a complex process during which cells undergo genetic and epigenetic alterations. These changes can lead tumor cells to acquire characteristics that enable movement from the primary site of origin when conditions become unfavorable. Such characteristics include gain of front-rear polarity, increased migration/invasion, and resistance to anoikis, which facilitate tumor survival during metastasis. An epithelial to mesenchymal transition (EMT) constitutes one way that cancer cells can gain traits that promote tumor progression and metastasis. Two microRNA (miRNA) families, the miR-200 and miR-221 families, play crucial opposing roles that affect the differentiation state of breast cancers. These two families are differentially expressed between the luminal A subtype of breast cancer as compared to the less well-differentiated triple negative breast cancers (TNBCs) that exhibit markers indicative of an EMT. The miR-200 family promotes a well-differentiated epithelial phenotype, while high miR-221/222 results in a poorly differentiated, mesenchymal-like phenotype. This review focuses on the mechanisms (specific proven targets) by which these two miRNA families exert opposing effects on cellular plasticity during breast tumorigenesis and metastasis.

Constitutive activation of the ETS-1-miR-222 circuitry in metastatic melanoma

MicroRNAs-221 and -222 are highly upregulated in several solid tumors, including melanomas. We demonstrate that the proto-oncogene ETS-1, involved in the pathogenesis of cancers of different origin, is a transcriptional regulator of miR-222 by direct binding to its promoter region. Differently from 293FT cells or early stage melanomas, where unphosphorylated ETS-1 represses miR-222 transcription, in metastatic melanoma the constitutively Thr-38 phosphorylated fraction of ETS-1 induces miR-222. Despite its stepwise decreased expression along with melanoma progression, the oncogenic activity of ETS-1 relies on its RAS/RAF/ERK-dependent phosphorylation status more than on its total amount. To close the loop, we demonstrate ETS-1 as a direct target of miR-222, but not miR-221, showing the novel option of their uncoupled functions. In addition, a spatial redistribution of ETS-1 protein from the nucleus to the cytoplasm is also evidenced in advanced melanoma cells. Finally, in vivo studies confirmed the contribution of miR-222 to the increased invasive potential obtained by ETS- silencing.

Integrative network analysis identifies key genes and pathways in the progression of hepatitis C virus induced hepatocellular carcinoma

Background

Incidence of hepatitis C virus (HCV) induced hepatocellular carcinoma (HCC) has been increasing in the United States and Europe during recent years. Although HCV-associated HCC shares many pathological characteristics with other types of HCC, its molecular mechanisms of progression remain elusive.

Methods

To investigate the underlying pathology, we developed a systematic approach to identify deregulated biological networks in HCC by integrating gene expression profiles with high-throughput protein-protein interaction data. We examined five stages including normal (control) liver, cirrhotic liver, dysplasia, early HCC and advanced HCC.

Results

Among the five consecutive pathological stages, we identified four networks including precancerous networks (Normal-Cirrhosis and Cirrhosis-Dysplasia) and cancerous networks (Dysplasia-Early HCC, Early-Advanced HCC). We found little overlap between precancerous and cancerous networks, opposite to a substantial overlap within precancerous or cancerous networks. We further found that the hub proteins interacted with HCV proteins, suggesting direct interventions of these networks by the virus. The functional annotation of each network demonstrates a high degree of consistency with current knowledge in HCC. By assembling these functions into a module map, we could depict the stepwise biological functions that are deregulated in HCV-induced hepatocarcinogenesis. Additionally, these networks enable us to identify important genes and pathways by developmental stage, such as LCK signalling pathways in cirrhosis, MMP genes and TIMP genes in dysplastic liver, and CDC2-mediated cell cycle signalling in early and advanced HCC. CDC2 (alternative symbol CDK1), a cell cycle regulatory gene, is particularly interesting due to its topological position in temporally deregulated networks.

Conclusions

Our study uncovers a temporal spectrum of functional deregulation and prioritizes key genes and pathways in the progression of HCV induced HCC. These findings present a wealth of information for further investigation.

Smooth muscle α-actin is a direct target of PLZF: effects on the cytoskeleton and on susceptibility to oncogenic transformation

Changes in cell morphology and rearrangements of the actin cytoskeleton are common features accompanying cell transformation induced by various oncogenes. In this study, we show that promyelocytic leukemia zinc finger protein (PLZF) binds to the promoter of smooth muscle α-actin, reducing mRNA and protein levels encoded by this gene and resulting in a reorganization of the actin cytoskeleton. In cultures of chicken embryo fibroblasts (CEF), this effect on α-actin expression is correlated with a change in cellular phenotype from spindle shaped to polygonal and flattened. This morphological change is dependent on Ras function. The polygonal, flattened CEF show a high degree of resistance to the transforming activity of several oncoproteins. Our results support the conclusion that reorganization of the actin cytoskeleton plays an important role in tumor suppression by PLZF.

An ATIPical family of angiotensin II AT2 receptor-interacting proteins

AT2, the second subtype of angiotensin II receptors, is a major component of the renin-angiotensin system involved in cardiovascular and neuronal functions. AT2 belongs to the superfamily of G protein-coupled receptors, but its intracellular signaling pathways have long remained elusive. Over the past few years, efforts to characterize this atypical receptor have led to the identification of novel molecular scaffolds that directly bind to its intracellular tail. The present review focuses on a family of AT2 receptor-interacting proteins (ATIPs) involved in neuronal differentiation, vascular remodeling and tumor suppression. Recent findings that ATIPs and ATIP-related proteins associate with microtubules suggest that they might constitute a novel family of multifunctional proteins regulating a wide range of physiopathological functions.

Cloning of cDNA and prediction of peptide structure of Plzf expressed in the spermatogonial cells of Labeo rohita

The promyelocytic leukemia zinc finger (Plzf) gene containing an evolutionary conserved BTB (bric-a-brac/tramtrack/broad complex) domain plays a key role in self-renewal of mammalian spermatogonial stem cells (SSCs) via recruiting transcriptional co-repressors. Little is known about the function of Plzf in vertebrate, especially in fish species. To gain better understanding of its role in fishes, we have cloned Plzf from the testis of Labeo rohita (rohu), a commercially important freshwater carp. The full-length cDNA contains an open reading frame (ORF) of 2004bp translatable to 667 amino acids (aa) containing a conserved N-terminal BTB domain and C-terminal C(2)H(2)-zinc finger motifs. L. rohita Plzf, which is phylogenetically related to Danio rerio counterpart, abundantly expressed in spermatogonial stem cells (SSCs). A three-dimensional (3D) model of BTB domain of Plzf protein was constructed by homology modeling approach. Molecular docking on this 3D structure established a homo-dimer between two BTB domains creating a charged pocket containing conserved aa residues: L33, C34, D35 and R49. Thus, Plzf of SSC is structurally and possibly functionally conserved. The conserved aa residues in the cleft resulting from Plzf BTB self-association are likely to be the binding platform for interaction with recruited co-repressor peptides. The identified Plzf could be the first step towards exploring its role in rohu SSC behavior.

PLZF/ZBTB16, a glucocorticoid response gene in acute lymphoblastic leukemia, interferes with glucocorticoid-induced apoptosis

Glucocorticoids (GCs) cause cell cycle arrest and apoptosis in lymphoid cells which is exploited to treat lymphoid malignancies. The mechanisms of these anti-leukemic GC effects are, however, poorly understood. We previously defined a list of GC-regulated genes by expression profiling in children with acute lymphoblastic leukemia (ALL) during systemic GC monotherapy and in experimental systems of GC-induced apoptosis. PLZF/ZBTB16, a transcriptional repressor, was one of the most promising candidates derived from this screen. To investigate its role in the anti-leukemic GC effects, we performed overexpression and knock-down experiments in CCRF-CEM childhood ALL cells. Transgenic PLZF/ZBTB16 alone had no detectable effect on cell proliferation or survival, but reduced sensitivity to GC-induced apoptosis but not apoptosis induced by antibodies against Fas/CD95 or 3 different chemotherapeutics. Knock-down of ZBTB16 entailed a small, but significant, increase in cell death induction by GC. Affymetrix Exon array-based whole genome expression profiling revealed that PLZF/ZBTB16 induction did not significantly alter the expression profile, however, it interfered with the regulation of numerous GC response genes, including BCL2L11/Bim, which has previously been shown to be responsible for cell death induction in CCRF-CEM cells. Thus, the protective effect of PLZF/ZBTB16 can be attributed to interference with transcriptional regulation by GC.

Expression of leukemia/lymphoma-related factor (LRF/POKEMON) in human breast carcinoma and other cancers

The POK family of proteins plays an important role in not only embryonic development and cell differentiation, but also in oncogenesis. Leukemia/lymphoma-related factor (LRF) belongs to the POK family of transcriptional repressors and is also known as POK erythroid myeloid ontogenic factor (POKEMON), which binds to short transcripts of HIV-1 (FBI-1) and TTF-1 interacting peptide (TIP21). Its oncogenic role is known only in lymphoma, non-small cell lung carcinoma, and malignant gliomas. The functional expression of LRF in human breast carcinoma has not yet been confirmed. The aim of this study was to investigate and compare the expression of LRF in human breast cancer tissues and other human tumors. The expression of LRF mRNA transcripts and protein was observed in twenty human benign and malignant breast biopsy tissues. Expression of LRF was observed in several formalin-fixed tissues by immunohistochemistry and immunofluorescence. All malignant breast tissues expressed mRNA transcripts and protein for LRF. However, 40% and 15% benign breast biopsy tissues expressed LRF mRNA transcripts and protein, respectively. The overall expression of LRF mRNA transcripts and total protein was significantly more in malignant breast tissues than the benign breast tissues. LRF expression was also observed in the nuclei of human colon, renal, lung, hepatocellular carcinomas and thymoma tumor cells. In general, a significantly higher expression of LRF was seen in malignant tissues than in the corresponding benign or normal tissue. Further studies are warranted to determine the malignant role of LRF in human breast carcinoma.

The promyelocytic leukemia zinc-finger gene, PLZF, is frequently downregulated in malignant mesothelioma cells and contributes to cell survival

DNA copy number analysis was performed, using single-nucleotide polymorphism mapping arrays, to fine map genomic imbalances in human malignant mesothelioma (MM) cell lines derived from primary tumors. Chromosomal losses accounted for the majority of genomic imbalances. All 22 cell lines examined showed homozygous deletions of 9p21.3, centering at the CDKN2A/ARF and CDKN2B loci. Other commonly underrepresented segments included 1p36, 1p22, 3p21-22, 4q13, 4q34, 11q23, 13q12-13, 14q32, 15q15, 18q12, and 22q12, each observed in 55-90% of cell lines. Focal deletions of 11q23 encompassed the transcriptional repressor gene promyelocytic leukemia zinc finger (PLZF), which was validated by analysis of genomic DNA using real-time polymerase chain reaction (PCR). Semi-quantitative RT-PCR and immunoblot analysis revealed that PLZF is greatly downregulated in MM cell lines compared with non-malignant mesothelial cells. Ectopic expression of PLZF in PLZF-deficient MM cells resulted in decreased cell viability, reduced colony formation, as well as increased apoptosis, the latter based on results of various cell death assays and the observation of increased cleavage of caspase 3, PARP, and Mcl-1. These data indicate that deletions of PLZF are a common occurrence in MM and that downregulation of PLZF may contribute to MM pathogenesis by promoting cell survival.

Genes and gene expression modules associated with caloric restriction and aging in the laboratory mouse

BACKGROUND

Caloric restriction (CR) counters deleterious effects of aging and, for most mouse genotypes, increases mean and maximum lifespan. Previous analyses of microarray data have identified gene expression responses to CR that are shared among multiple mouse tissues, including the activation of anti-oxidant, tumor suppressor and anti-inflammatory pathways. These analyses have provided useful research directions, but have been restricted to a limited number of tissues, and have focused on individual genes, rather than whole-genome transcriptional networks. Furthermore, CR is thought to oppose age-associated gene expression patterns, but detailed statistical investigations of this hypothesis have not been carried out.

RESULTS

Systemic effects of CR and aging were identified by examining transcriptional responses to CR in 17 mouse tissue types, as well as responses to aging in 22 tissues. CR broadly induced the expression of genes known to inhibit oxidative stress (e.g., Mt1, Mt2), inflammation (e.g., Nfkbia, Timp3) and tumorigenesis (e.g., Txnip, Zbtb16). Additionally, a network-based investigation revealed that CR regulates a large co-expression module containing genes associated with the metabolism and splicing of mRNA (e.g., Cpsf6, Sfpq, Sfrs18). The effects of aging were, to a considerable degree, similar among groups of co-expressed genes. Age-related gene expression patterns characteristic of most mouse tissues were identified, including up regulation of granulin (Grn) and secreted phosphoprotein 1 (Spp1). The transcriptional association between CR and aging varied at different levels of analysis. With respect to gene subsets associated with certain biological processes (e.g., immunity and inflammation), CR opposed age-associated expression patterns. However, among all genes, global transcriptional effects of CR were only weakly related to those of aging.

CONCLUSION

The study of aging, and of interventions thought to combat aging, has much to gain from data-driven and unbiased genomic investigations. Expression patterns identified in this analysis characterize a generalized response of mammalian cells to CR and/or aging. These patterns may be of importance in determining effects of CR on overall lifespan, or as factors that underlie age-related disease. The association between CR and aging warrants further study, but most evidence indicates that CR does not induce a genome-wide "reversal" of age-associated gene expression patterns.

Posttranslational regulation of Myc by promyelocytic leukemia zinc finger protein

The promyelocytic leukemia zinc finger (PLZF) protein, a transcriptional repressor, induces cellular resistance to oncogenic transformation by diverse oncoproteins. Two point mutants of PLZF that have lost the antioncogenic activity of the wild-type protein are oncogenic in chicken embryo fibroblasts; this activity is correlated with differential effects on Myc. Wild-type PLZF represses Myc transcription without affecting total Myc protein levels and reduces the levels of phosphorylated Myc. The PLZF mutants do not alter Myc transcription or protein expression but increase the levels of phosphorylated Myc. These modifications of Myc are correlated with PLZF-induced changes in Akt and the mitogen-activated protein kinase (MAPK) pathway. Wild-type PLZF downregulates the MAPK pathway and activates Akt, resulting in reduced phosphorylation on serine 62 of Myc by Erk and on threonine 58 by glycogen synthase kinase 3beta. The mutants fail to activate Akt and only slightly downregulate phospho-Erk. We postulate that the 2 PLZF mutants are oncogenic, because they function as dominant negatives of wild-type PLZF, enhancing Myc phosphorylation and increasing Myc transcriptional and oncogenic activity. In support of this suggestion, a specific inhibitor of Myc is able to revert the transformed phenotype of PLZF mutant-expressing cells.

Caveolin-1 tumor-promoting role in human melanoma

Caveolin-1 (Cav-1), a member of the caveolin family, regulates caveolae-associated signaling proteins, which are involved in many biological processes, including cancer development. Cav-1 was found to exert a complex and ambiguous role as oncogene or tumor suppressor depending on the cellular microenvironment. Here we investigated Cav-1 expression and function in a panel of melanomas, finding its expression in all the cell lines. The exception was the primary vertical melanoma cell line, WM983A, characterized by the lack of Cav-1, and then utilized as a recipient for Cav-1 gene transduction to address a series of functional studies. The alleged yet controversial role of phospho (Ph)-Cav-1 on cell regulation was also tested by transducing the nonphosphorylatable Cav-1Y14A mutant. Wild-type Cav-1, but not mutated Cav-1Y14A, increased tumorigenicity as indicated by enhanced proliferation, migration, invasion and capacity of forming foci in semisolid medium. Accordingly, Cav-1 silencing inhibited melanoma cell growth reducing some of the typical traits of malignancy. Finally, we detected a secreted fraction of Cav-1 associated with cell released microvesicular particles able to stimulate in vitro anchorage independence, migration and invasion in a paracrine/autocrine fashion and, more important, competent to convey metastatic asset from the donor melanoma to the less aggressive recipient cell line. A direct correlation between Cav-1 levels, the amount of microvesicles released in the culture medium and MMP-9 expression was also observed.

PLZF-mediated control on c-kit expression in CD34(+) cells and early erythropoiesis

The promyelocytic leukemia zinc-finger protein (PLZF) is a transcription factor and c-kit is a receptor tyrosine kinase associated with human disease, particularly in hematopoietic cells. MicroRNAs (miRs) are post-transcriptional regulators of gene expression, and c-kit has been described as a target of miRs-221 and -222 in erythropoiesis. In the present study, we identified c-kit as a target of PLZF in normal and leukemic cells. Particularly, in erythropoietic (E) culture of CD34(+) progenitors, PLZF is downregulated, whereas c-kit expression at both the mRNA and protein levels inversely increases during the first days of E differentiation. In functional experiments, PLZF transfection induces c-kit downregulation, inhibits E proliferation and delays differentiation, whereas PLZF knockdown induces opposite effects, independently of miRs-221 and -222 expression. The inverse correlation between PLZF and c-kit expression was found in normal CD34(+)38(+/-) hematopoietic progenitor/stem cells and in acute myeloid leukemias of M0/M1 French-American-British subtypes, suggesting that the control of PLZF on c-kit expression may be crucial at the level of the stem cell/progenitor compartment. Altogether, our data indicate a new mechanism of regulation of c-kit expression that involves a transcriptional control by PLZF in CD34(+) cells and early erythropoiesis.

MicroRNAs and the skin: tiny players in the body's largest organ

MicroRNAs (miRNAs) are very small endogenous RNA molecules about 22-25 nucleotides in length, capable of post-transcriptional gene regulation. miRNAs bind to their target messenger RNAs (mRNAs), leading to cleavage or suppression of target mRNA translation based on the degree of complementarity. miRNAs have recently been shown to play pivotal roles in diverse developmental and cellular processes and linked to a variety of skin diseases and cancers. Disruption of miRNA metabolism is also involved in wound healing and inflammatory skin conditions. Here, we review the role of miRNAs in cutaneous biology.

Increased expression of the tumor suppressor PLZF is a continuous predictor of long-term survival in malignant melanoma patients

Promyelocytic leukemia zinc finger (PLZF) is a transcriptional repressor and tumor suppressor inhibiting melanoma cell growth in vitro and in vivo in animal models. In this study, we analyzed the impact of in vivo primary tumor gene expression of PLZF on the long-term survival of malignant melanoma patients. PLZF expression was assessed by using DNA microarray and real-time polymerase chain reaction analysis of 41 primary malignant melanomas from patients with a defined histology and a close to 20-year clinical follow-up, of 29 melanoma metastases, and of 6 different melanoma cell lines. Kaplan-Meier survival analyses, log-rank statistics and Cox regression analysis were employed to identify the impact of PLZF expression on long-term survival. We detected PLZF expression in 92% of primary melanoma tumors in vivo but not in melanoma cell lines in vitro. By univariate analysis, we identified: (1) PLZF mRNA expression < or = 10,000 mRNA copies/mug total tumor RNA, (2) Breslow tumor thickness >4 mm, and (3) American Joint Committee on Cancer stages IIC, IIIB, IIIC, and IV as statistically significant pretreatment risk factors. We defined a continuous prognostic index (i.e., risk score) for primary melanoma patients based on the regression coefficient of PLZF mRNA expression. Applying a cutpoint to the prognostic index at - 1.65, patients were assigned to one of two risk groups: low-risk patients (n = 28) with a median overall survival of 79 months (5-year survival of 61%) and high-risk patients (n = 13) with a median overall survival of 32 months (5-year survival of 23%) (p < 0.05). This is the first time that PLZF mRNA expression has been linked to a prognostic model for primary malignant melanoma patients to derive prognostic groups for clinical purposes (e.g., improved melanoma immunotherapies).

The GTPase domain of Galphao contributes to the functional interaction of Galphao with the promyelocytic leukemia zinc finger protein

Go, one of the most abundant heterotrimeric G proteins in the brain, is classified as a member of the Gi/Go family based on its homology to Gi proteins. Recently, we identified promyelocytic leukemia zinc finger protein (PLZF) as a candidate downstream effector for the alpha subunit of Go (Gαo). Activated Gαo interacts with PLZF and augments its function as a repressor of transcription and cell growth. G protein-coupled receptor-mediated Gαo activation also enhanced PLZF function. In this study, we determined that the GTPase domain of Gαo contributes to Gαo:PLZF interaction. We also showed that the Gαo GTPase domain is important in modulating the function of PLZF. This data indicates that the GTPase domain of Gαo may be necessary for the functional interaction of Gαo with PLZF.

Functional integration of microRNAs into oncogenic and tumor suppressor pathways

A large body of evidence has documented abnormal microRNA (miRNA) expression patterns in diverse human malignancies. Given that miRNA expression is tightly regulated during development and cellular differentiation, aberrant miRNA expression in cancer cells is likely to be in part a consequence of the loss of normal cellular identity that accompanies malignant transformation. Nevertheless, it is now clear that miRNAs function as critical effectors of several canonical oncogenic and tumor suppressor pathways, including those controlled by Myc and p53. Gain- and loss-of-function of these factors in cancer cells contributes to miRNA dysregulation, directly influencing neoplastic phenotypes including cellular proliferation and apoptosis.

A three-step pathway comprising PLZF/miR-146a/CXCR4 controls megakaryopoiesis

MicroRNAs (miRNAs or miRs) regulate diverse normal and abnormal cell functions. We have identified a regulatory pathway in normal megakaryopoiesis, involving the PLZF transcription factor, miR-146a and the SDF-1 receptor CXCR4. In leukaemic cell lines PLZF overexpression downmodulated miR-146a and upregulated CXCR4 protein, whereas PLZF knockdown induced the opposite effects. In vitro assays showed that PLZF interacts with and inhibits the miR-146a promoter, and that miR-146a targets CXCR4 mRNA, impeding its translation. In megakaryopoietic cultures of CD34(+) progenitors, PLZF was upregulated, whereas miR-146a expression decreased and CXCR4 protein increased. MiR-146a overexpression and PLZF or CXCR4 silencing impaired megakaryocytic (Mk) proliferation, differentiation and maturation, as well as Mk colony formation. Mir-146a knockdown induced the opposite effects. Rescue experiments indicated that the effects of PLZF and miR-146a are mediated by miR-146a and CXCR4, respectively. Our data indicate that megakaryopoiesis is controlled by a cascade pathway, in which PLZF suppresses miR-146a transcription and thereby activates CXCR4 translation.

The promyelocytic leukemia zinc finger-microRNA-221/-222 pathway controls melanoma progression through multiple oncogenic mechanisms

The incidence of cutaneous melanoma is steadily increasing. Although several molecular abnormalities have been associated with melanoma progression, the mechanisms underlying the differential gene expression are still largely unknown and targeted therapies are not yet available. Noncoding small RNAs, termed microRNAs (miR), have been recently reported to play important roles in major cellular processes, including those involved in cancer development and progression. We have identified the promyelocytic leukemia zinc finger (PLZF) transcription factor as a repressor of miR-221 and miR-222 by direct binding to their putative regulatory region. Specifically, PLZF silencing in melanomas unblocks miR-221 and miR-222, which in turn controls the progression of the neoplasia through down-modulation of p27Kip1/CDKN1B and c-KIT receptor, leading to enhanced proliferation and differentiation blockade of the melanoma cells, respectively. In vitro and in vivo functional studies, including the use of antisense "antagomir" oligonucleotides, confirmed the key role of miR-221/-222 in regulating the progression of human melanoma; this suggests that targeted therapies suppressing miR-221/-222 may prove beneficial in advanced melanoma.

Osteonectin downregulates E-cadherin, induces osteopontin and focal adhesion kinase activity stimulating an invasive melanoma phenotype

Osteonectin is recognised as a marker of metastasis progression in melanoma and has been implicated in the transition from radial to vertical growth phase. A Tetracycline-inducible system was used to regulate Osteonectin protein levels in melanoma cell lines to examine the morphological, biochemical and invasive changes that accompany its altered expression. Assay of protein and phosphorylation changes showed a downregulation of E-cadherin, upregulation of Osteopontin and a corresponding increase in phosphorylation of Focal Adhesion Kinase on Tyr(397) and Tyr(576) concomitant with Osteonectin induction. Melanoma cells overexpressing Osteonectin displayed increased invasive potential, whereas ablation of Osteonectin gene transcription using siRNA suppressed the invasive potential of these cells and resulted in the upregulation of E-cadherin. The recently described interaction of Osteonectin with Integrin Linked Kinase leading to modulation of its activity suggests a mechanism relevant to the loss of E-cadherin and cell adhesion that occurs during melanoma progression. These results indicate a central role for Osteonectin in the regulation of gene expression changes driving the progression of melanoma toward metastasis.

Identification of apoptosis-related PLZF target genes

The PLZF gene encodes a BTB/POZ-zinc finger-type transcription factor, involved in physiological development, proliferation, differentiation, and apoptosis. In this paper, we investigate proliferation, survival, and gene expression regulation in stable clones from the human haematopoietic K562, DG75, and Jurkat cell lines with inducible expression of PLZF. In Jurkat cells, but not in K562 and DG75 cells, PLZF induced growth suppression and apoptosis in a cell density-dependent manner. Deletion of the BTB/POZ domain of PLZF abrogated growth suppression and apoptosis. PLZF was expressed with a nuclear speckled pattern distinctively in the full-length PLZF-expressing Jurkat clones, suggesting that the nuclear speckled localization is required for PLZF-induced apoptosis. By microarray analysis, we identified that the apoptosis-inducer TP53INP1, ID1, and ID3 genes were upregulated, and the apoptosis-inhibitor TERT gene was downregulated. The identification of apoptosis-related PLZF target genes may have biological and clinical relevance in cancer typified by altered PLZF expression.

A new hepatocytic isoform of PLZF lacking the BTB domain interacts with ATP7B, the Wilson disease protein, and positively regulates ERK signal transduction

The promyelocytic leukemia zinc finger (PLZF) protein has been described as a transcriptional repressor of the BTB-domain/zinc-finger family, and shown to regulate the expression of Hox genes during embryogenesis and the expression of cyclin A in the cell cycle progression. Here, a 45-kDa isoform of PLZF without a BTB domain was identified via yeast two-hybrid screening using the C-terminal region of ATP7B as bait in our determination of the biological roles of the Wilson disease protein outside of its copper-binding domain. Our immunoprecipitation experiments showed that the hepatocytic isoform of PLZF could specifically interact with the C-terminal region of ATP7B. The immunostaining of HepG2 cells revealed that the ATP7B and PLZF proteins were apparently colocalized into the trans-Golgi complexes. It was also determined that disruption of PLZF expression in the HepG2 cells affected an attenuation of ERK activity in a dose-dependent manner. The hepatocytic activities of ERK kinase were found to be enhanced as the result of PLZF or ATP7B expression, but this enhancement was abrogated by the deletion of the C-terminal region of ATP7B. Furthermore, a transgenic Drosophila strain that ectopically expressed the hepatocytic deltaBTB-PLZF exhibited phenotypic changes in eye and wing development, and these alterations were fully recovered as the result of ATP7B expression, indicating the obvious in vivo interaction between the two proteins. Those PLZF-induced abnormalities were attributed to the enhancement of ERK signaling, as was shown by phenotypic reversions with loss-of-function mutations in ERK signal transduction in Drosophila. These data suggest the existence of a mechanism that regulates ERK signaling via the C-terminus of ATP7B and the ATP7B-interacting hepatocytic PLZF.

The PLZF gene of t (11;17)-associated APL

The PLZF gene is one of five partners fused to the retinoic acid receptor alpha in acute promyelocytic leukemia. PLZF encodes a DNA-binding transcriptional repressor and the PLZF-RARalpha fusion protein like other RARalpha fusions can inhibit the genetic program mediated by the wild tpe retinoic acid receptor. However an increasing body of literature indicates an important role for the PLZF gene in growth control and development. This information suggests that loss of PLZF function might also contribute to leukemogenesis.

Pre-B-cell leukemia transcription factor 1 is a major target of promyelocytic leukemia zinc-finger-mediated melanoma cell growth suppression

Promyelocytic leukemia zinc-finger (PLZF) is a transcriptional repressor and tumor suppressor. PLZF is expressed in melanocytes but not in melanoma cells, and recovery of PLZF expression markedly suppresses melanoma cell growth. Several target genes regulated by PLZF have been identified, but the precise function of PLZF remains uncertain. Here, we searched for candidate target genes of PLZF by DNA microarray analysis. Pre-B-cell leukemia transcription factor 1 (Pbx1) was one of the prominently suppressed genes. Pbx1 was highly expressed in melanoma cells, and its expression was reduced by transduction with the PLZF gene. Moreover, the growth suppression mediated by PLZF was reversed by enforced expression of Pbx1. Knockdown of Pbx1 by specific small interfering RNAs suppressed melanoma cell growth. We also found that Pbx1 binds HoxB7. Reverse transcription-polymerase chain reaction analysis demonstrated that repression of Pbx1 by PLZF reduces the expression of HoxB7 target genes, including tumor-associated neoangiogenesis factors such as basic fibroblast growth factor, angiopoietin-2 and matrix metalloprotease 9. These findings suggest that deregulation of Pbx1 expression owing to loss of PLZF expression contributes to the progression and/or pathogenesis of melanoma.

SPARC represses E-cadherin and induces mesenchymal transition during melanoma development

During progression of melanoma, loss of the cell-cell adhesion molecule E-cadherin contributes to uncontrolled growth and invasive behavior of transformed melanocytes. Secreted protein acidic and rich in cysteine (SPARC) is a nonstructural matricellular protein that regulates cell-matrix interactions leading to alterations in cell adhesion and proliferation. Overexpression of SPARC has been associated with progression of various cancers, including melanoma; however, its role in primary tumor development is not well defined. We show that normal human melanocytes overexpressing SPARC adopt a fibroblast-like morphology, concomitant with loss of E-cadherin and P-cadherin expression, and increased expression of mesenchymal markers. Concurrent with these changes, SPARC expression stimulates melanocyte motility and melanoma cell invasion. Expression of SPARC results in transcriptional down-regulation of E-cadherin that correlates with induction of Snail, a repressor of E-cadherin. Conversely, SPARC depletion leads to up-regulation of E-cadherin and reduces Snail levels, and SPARC-null cells exhibit a marked change in their mesenchymal phenotype. Finally, analysis of SPARC, Snail, and E-cadherin levels in melanocytes and malignant melanoma cell lines further supports the functional relationship among these proteins during melanoma progression. Our findings provide evidence for the role of SPARC in early transformation of melanocytes and identify a novel mechanism, whereby tumor-derived SPARC promotes tumorigenesis by mediating Snail induction and E-cadherin suppression.