Deregulated homeobox gene expression in cancer: cause or consequence?

Lineage dependency and lineage-survival oncogenes in human cancer

Although cell-lineage and differentiation models dominate tumour classification and treatment, the recognition that cancer is also a genomic disease has prompted a reconfiguration of cancer taxonomies according to molecular criteria. Recent evidence indicates that a synthesis of lineage-based and genetic paradigms might offer new insights into crucial and therapeutically pliable tumour dependencies. For example, MITF (microphthalmia-associated transcription factor), which is a master regulator of the melanocyte lineage, might become a melanoma oncogene when deregulated in certain genetic contexts. MITF and other lineage-survival genes therefore implicate lineage dependency (or lineage addiction) as a newly recognized mechanism that is affected by tumour genetic alterations.

Acute monocytic leukemia with coexpression of minor BCR-ABL1 and PICALM-MLLT10 fusion genes along with overexpression of HOXA9

The t(9;22)(q34;q11) translocation occurs in chronic myeloid leukemia (CML) and adult B-cell acute lymphoblastic leukemia (ALL), leading to fusion of BCR to ABL1 and constitutive activation of ABL1 tyrosine kinase activity. The main BCR-ABL1 breakpoints result in P190 BCR-ABL1 or P210 BCR-ABL1 fusion proteins. The latter is found in almost all cases of CML and in one third of the cases of t(9;22)-positive adult B-ALL. P190 BCR-ABL1 is found in the remaining two thirds of t(9;22)-positive adult B-ALL cases but only exceptionally in CML. We describe here the first case of t(9;22)(q34;q11) associated with t(10;11)(p13;q14) in acute monocytic leukemia. The recurrent t(10;11)(p13;q14) translocation, usually found in acute myeloid leukemia (AML) and T-ALL, merges PICALM to MLLT10. RT-PCR enabled identification of PICALM-MLLT10 and BCR-ABL1 e1-a2 fusion transcripts; in the context of chronic and acute myeloid leukemia, the latter usually has a monocytic presentation. We also identified overexpression of HOXA9, a gene essential to myeloid differentiation that is expressed in PICALM-MLLT10 and MLL-rearranged acute leukemias. This case fits with and extends a recently proposed multistage AML model in which constitutive activation of tyrosine kinases by mutations (BCR-ABL1) are associated with deregulation of transcription factors central to myeloid differentiation (HOXA9 secondary to PICALM-MLLT10).

A two-gene expression ratio of homeobox 13 and interleukin-17B receptor for prediction of recurrence and survival in women receiving adjuvant tamoxifen

PURPOSE

In the adjuvant treatment of estrogen receptor (ER)-positive breast cancer, additional markers are needed to identify women at high risk for recurrence.

EXPERIMENTAL DESIGN

We examined the association between the ratio of the homeobox 13 (HOXB13) to interleukin-17B receptor (IL-17BR) expression and the clinical outcomes of relapse and survival in women with ER-positive breast cancer enrolled onto a North Central Cancer Treatment Group adjuvant tamoxifen trial (NCCTG 89-30-52).

RESULTS

Tumor blocks were obtained from 211 of 256 eligible patients, and quantitative reverse transcription-PCR profiles for HOXB13 and IL-17BR were obtained from 206 patients. The cut point for the two-gene log 2(expression ratio) that best discriminated clinical outcome (recurrence and survival) was selected and identified women with significantly worse relapse-free survival (RFS), disease-free survival (DFS), and overall survival (OS), independent of standard prognostic markers. The cut point differed as a function of nodal status [node negative (59th percentile) versus node positive (90th percentile)]. In the node-positive cohort (n = 86), the HOXB13/IL-17BR ratio was not associated with relapse or survival. In contrast, in the node-negative cohort (n = 130), a high HOXB13/IL-17BR ratio was associated with significantly worse RFS [hazard ratio (HR), 1.98; P = 0.031], DFS (HR, 2.03; P = 0.015), and OS (HR, 2.4; P = 0.014), independent of standard prognostic markers.

CONCLUSION

A high HOXB13/IL-17BR expression ratio is associated with increased relapse and death in patients with resected node-negative, ER-positive breast cancer treated with tamoxifen and may identify patients in whom alternative therapies should be studied.

A high-throughput gene knockout procedure for Neurospora reveals functions for multiple transcription factors

The low rate of homologous recombination exhibited by wild-type strains of filamentous fungi has hindered development of high-throughput gene knockout procedures for this group of organisms. In this study, we describe a method for rapidly creating knockout mutants in which we make use of yeast recombinational cloning, Neurospora mutant strains deficient in nonhomologous end-joining DNA repair, custom-written software tools, and robotics. To illustrate our approach, we have created strains bearing deletions of 103 Neurospora genes encoding transcription factors. Characterization of strains during growth and both asexual and sexual development revealed phenotypes for 43% of the deletion mutants, with more than half of these strains possessing multiple defects. Overall, the methodology, which achieves high-throughput gene disruption at an efficiency >90% in this filamentous fungus, promises to be applicable to other eukaryotic organisms that have a low frequency of homologous recombination.

Identification of a Hoxc8-regulated transcriptional network in mouse embryo fibroblast cells

The transcription factor, Hoxc8, is a member of the homeobox gene family that is vital for growth and differentiation. Previously, we identified 34 genes whose expression levels were changed at least 2-fold by forced expression of Hoxc8 in C57BL/6J mouse embryo fibroblast cells using a mouse 16,463-gene oligonucleotide microarray. In the present study, we used the combined power of microarray profiling, global Hoxc8 DNA-binding site analysis, and high-throughput chromatin immunoprecipitation assays to identify direct and biologically relevant targets of Hoxc8 in vivo. Here we show that 19 of the 34 responsive genes contain Hoxc8 consensus DNA-binding sequence(s) in their regulatory regions. Chromatin immunoprecipitation analysis indicated that Hoxc8-DNA interaction was detected in five of the 19 candidate genes. All of these five target genes have been implicated in oncogenesis, cell adhesion, proliferation, and apoptosis. Overall, the genes described here should aid in the understanding of global regulatory networks of Hox genes and to provide valuable insight into the molecular basis of Hoxc8 in development and carcinogenesis.

CDX2 has tumorigenic potential in the human colon cancer cell lines LOVO and SW48

CDX2 is a Drosophila caudal-related homeobox transcription factor that is important for the establishment and maintenance of intestinal epithelial cells. CDX2 is a marker of colon cancer, with strong staining in up to 90% of colonic adenocarcinomas. CDX2 heterozygous-null mice develop colonic neoplasms, which have suggested that CDX2 is a tumor suppressor. However, CDX2 has not been reported to affect xenograft growth. Furthermore, CDX2 is rarely mutated in colon cancer, which has led to suggestions that it may play only a minor role as a tumor suppressor in colon cancer. To understand the functional contributions of CDX2 to colon cancer, we disrupted CDX2 in LOVO and SW48 human colon cancer cell lines by targeted homologous recombination. Consistent with the literature, disruption of CDX2 enhanced anchorage-dependent cell proliferation. However, homozygous loss of CDX2 led to significant inhibition of anchorage-independent growth in LOVO cells, and cell lethality in SW48 cells. Further analyses revealed that disruption of CDX2 led to anchorage-independent G1 to S growth arrest and anoikis. In vivo xenograft studies confirmed that disruption of CDX2 inhibited LOVO tumor growth. These data demonstrate that CDX2 mediates anchorage-independent growth and survival. Thus, CDX2 has tumorigenic potential in the human colon cancer cell lines LOVO and SW48.

A role for Hox A5 in regulating angiogenesis and vascular patterning

BACKGROUND

Homeobox (Hox) genes are transcriptional regulators which modulate embryonic morphogenesis and pathological tissue remodeling in adults via regulation of genes associated with cell-cell or cell extracellular matrix (ECM) interactions. We previously showed that while Hox 3 genes promote angiogenesis, Hox D10 inhibits this process.

METHODS AND RESULTS

Here we show that another Hox family gene, Hox A5, also blocks angiogenesis but accomplishes this by targeting different downstream genes than Hox D10. Sustained expression of Hox A5 leads to down regulation of many pro-angiogenic genes including VEGFR2, ephrin A1, Hif1alpha and COX-2. In addition, Hox A5 also upregulates expression of anti-angiogenic genes including Thrombospondin-2. Furthermore, we show that while Hox A5 mRNA is expressed in quiescent endothelial cells (EC), its expression is diminished or absent in active angiogenic EC found in association with breast tumors or in proliferating infantile hemangiomas.

CONCLUSIONS

Together our results suggest that restoring Hox A5 expression may provide a novel means to limit breast tumor growth or expansion of hemangiomas.

Deregulation of the HOXA10 homeobox gene in endometrial carcinoma: role in epithelial-mesenchymal transition

Homeobox genes encode transcription factors that control cell differentiation and play essential roles in developmental patterning. Increasing evidence indicates that many homeobox genes are aberrantly expressed in cancers, and that their deregulation significantly contributes to tumor progression. The homeobox gene HOXA10 controls uterine organogenesis during embryonic development and functional endometrial differentiation in the adult. We investigated whether HOXA10 expression is deregulated in endometrial carcinomas, and how counteracting this aberrant expression modifies tumor behavior. We found that down-regulation of HOXA10 expression in endometrial carcinomas strongly correlates with increased tumor grade and is associated with methylation of the HOXA10 promoter. Enforced expression of HOXA10 in endometrial carcinoma cells inhibited invasive behavior in vitro and tumor dissemination in nude mice. The inhibitory effect of HOXA10 on invasive behavior was attributable at least in part to the ability of HOXA10 to induce expression of the epithelial cell adhesion molecule E-cadherin by down-regulating expression of Snail, a repressor of E-cadherin gene transcription. These findings reveal a novel role for HOXA10 deregulation in the progression of endometrial carcinoma by promoting epithelial-mesenchymal transition.

The putative tumor suppressor Cdx2 is overexpressed by human colorectal adenocarcinomas

PURPOSE

The current paradigm suggests that the homeodomain transcription factor Cdx2, which directs the development and maintenance of the intestinal epithelium, is a tumor suppressor in the colon and rectum. Although a cardinal property of tumor suppressors is their inactivation during carcinogenesis, the expression of Cdx2 in colorectal tumors has not been compared with that in normal mucosa. Here, Cdx2 expression and function was quantified in tumors and matched normal mucosa from patients with colorectal cancer.

EXPERIMENTAL DESIGN

Cdx2 expression was quantified by reverse transcription-PCR, immunoblot analysis, and immunohistochemistry. Transcriptional activity was explored by quantifying expression of an endogenous downstream target of Cdx2, guanylyl cyclase C (GCC), in tissues by quantitative reverse transcription-PCR and expression of exogenous Cdx2-specific luciferase promoter constructs in epithelial cells isolated from tumors and normal mucosa.

RESULTS

Most (>80%) colorectal tumors overexpressed Cdx2 mRNA and protein compared with normal mucosa, with median fold increases of 3.6 and 1.4, respectively (P<0.002). Concomitantly, immunohistochemistry revealed elevated levels of Cdx2 in nuclei of tumor cells compared with normal epithelial cells. Further, tumors exhibited increased expression of GCC compared with normal mucosa. Moreover, cells isolated from tumors overexpressed a Cdx2-specific luciferase promoter construct compared with normal mucosal cells.

CONCLUSION

These observations show, for the first time, the structural and functional overexpression of Cdx2 by human colorectal tumors compared with matched normal mucosa. They suggest that loss of Cdx2 expression or transcriptional activity is an infrequent event during tumorigenesis, which does not contribute to molecular mechanisms underlying initiation and progression of most colorectal tumors.

Increased CDX2 and decreased PITX1 homeobox gene expression in Barrett's esophagus and Barrett's-associated adenocarcinoma

BACKGROUND

The CDX2 (caudal-related homeobox gene 2) and PITX1 (pituitary homeobox 1) genes have essential roles in human development. Forced expression of Cdx2 alone in the murine stomach results in gastric intestinal metaplasia (IM). This study was undertaken to investigate the expression pattern of these critical morphogenesis genes in the Barrett's multistage carcinogenesis model.

METHODS

CDX2 and PITX1 messenger RNA (mRNA) expression levels, relative to the control gene beta-actin, were measured by reverse transcription-polymerase chain reaction in specimens of Barrett's IM (n = 21), dysplasia (n = 18), adenocarcinoma (n = 20), and matching normal squamous esophagus tissues (n = 39) collected from 19 patients with Barrett's esophagus and 20 patients with esophageal adenocarcinoma. CDX2 protein expression was assessed by immunohistochemistry in specimens of normal squamous esophagus (n = 13), IM (n = 10), dysplasia (n = 8,) and adenocarcinoma (n = 5).

RESULTS

The median relative CDX2 mRNA expression was approximately 200 times higher in Barrett's esophagus tissues (0.83) than in matching normal squamous esophagus (0.004) in the patients with Barrett's esophagus (P < .001). The mRNA expression in cancer tissues (0.49) was also higher than in matching normal squamous esophagus specimens (0.009, P < .001). There was no significant difference between the mRNA expression levels in Barrett's esophagus and adenocarcinoma. There was no CDX2 protein expression in normal squamous esophagus, but moderate to strong protein expression was seen in all Barrett's tissues and in a majority of the dysplasia and adenocarcinoma cells. Relative median PITX1 mRNA expression was decreased in Barrett's esophagus (8.02 for all specimens), compared with normal esophagus specimens (47.46 for all specimens, P < .001), and was further reduced in cancer specimens (2.21), compared with either Barrett's esophagus or normal esophagus (both P < .001). Wilcoxon testwas used for all P values shown.

CONCLUSIONS

CDX2 mRNA and CDX2 protein expression are upregulated in Barrett's IM tissues, compared with normal squamous esophagus, and remain elevated in dysplasia and adenocarcinoma tissues. In contrast, PITX1 mRNA expression is decreased in Barrett's esophagus, compared with matching normal squamous esophagus specimens, and is further decreased in Barrett's-associated cancer. These descriptive findings suggest a possible role for these genes in the Barrett's metaplasia-dysplasia-adenocarcinoma sequence.

Transcriptional census of 36 microdissected colorectal cancers yields a gene signature to distinguish UICC II and III

UICC stage II and III colorectal cancers (CRC) differ fundamentally in prognosis and therapeutic concepts. To analyze differential gene expression between both stages and to establish a relationship between molecular background and clinical presentation, tumor material from 36 unselected consecutive patients presenting with sporadic CRC, 18 UICC stage II and 18 UICC stage III, were laser microdissected to separate epithelial tumor cells. Gene expression levels were measured using U133A Affymetrix gene arrays. Twelve CRC associated signal transduction pathways as well as all 22,000 probe sets were screened for differential gene expression. We identified a signature consisting of 45 probe sets that allowed discrimination between UICC stage II and stage III with a rate of correct classification of about 80%. The most distinctive elements in this signature were the gene GSTP-binding elongation factor (GSPT2) and the transcription factor HOXA9. Differential expression of these genes was confirmed by quantitative real-time polymerase chain reaction (p(HOXA9) = 0.04, p(GSTP2) = 0.02). Despite the reliability of the presented data, there was no substantial differential expression of genes in cancer-related pathways. However, the comparison with recently published data corroborates the 45 gene signature showing structural agreement in the direction of fold changes of gene expression levels for our set of genes chosen to discriminate between both stages.

cAMP induced modifications of HOX D gene expression in prostate cells allow the identification of a chromosomal area involved in vivo with neuroendocrine differentiation of human advanced prostate cancers

The acquisition of epithelial-neuroendocrine differentiation (ND) is a peculiarity of human advanced, androgen-independent, prostate cancers. The HOX genes are a network of transcription factors controlling embryonal development and playing an important role in crucial adult eukaryotic cell functions. The molecular organization of this 39-gene network is unique in the genome and probably acts by regulating phenotype cell identity. The expression patterns of the HOX gene network in human prostate cell phenotypes, representing different stages of prostate physiology and prostate cancer progression, make it possible to discriminate between different human prostate cell lines and to identify loci and paralogous groups harboring the HOX genes mostly involved in prostate organogenesis and cancerogenesis. Exposure of prostate epithelial phenotypes to cAMP alters the expression of lumbo-sacral HOX D genes located on the chromosomal region 2q31-33 where the cAMP effector genes CREB1, CREB2, and cAMP-GEFII are present. Interestingly, this same chromosomal area harbors: (i) a global cis-regulatory DNA control region able to coordinate the expression of HOX D and contiguous phylogenetically unrelated genes; (ii) a prostate specific ncRNA gene associated with high-risk prostate cancer (PCGEM1); (iii) a series of neurogenic-related genes involved with epithelial-neuronal cell conversion. We report the expression of neurexin 1, Neuro D1, dlx1, and dlx2 in untreated and cAMP treated epithelial prostate cells. The in vivo expression of Neuro D1 in human advanced prostate cancers correlate with the state of tumor differentiation as measured by Gleason score. Thus, we suggest that the chromosomal area 2q 31-33 might be involved in the epithelial-ND characteristic of human advanced prostate cancers.

Phosphorylation of the homeotic tumor suppressor Cdx2 mediates its ubiquitin-dependent proteasome degradation

The Caudal-related homeodomain transcription factor Cdx2 plays a key role in intestinal cell fate determination. Reduction of Cdx2 expression is a feature of many human colon carcinomas and inactivation of one cdx2 allele facilitates the development of invasive adenocarcinoma in the murine colon. Here, we investigated the post-translational regulation of Cdx2. We showed that various forms of Cdx2 coexist in the intestine and colon cancer cell lines, some of them being phosphorylated forms. We found that cyclin-dependent kinase 2 phosphorylated Cdx2 in vitro and in vivo. Using site-specific mutagenesis, we identified serine 281 as a new key residue for Cdx2 phosphorylation. Intriguingly, serine 281 belongs to a conserved motif of four evenly spaced serines (the 4S motif) similar to the one controlling beta-catenin degradation by the proteasome pathway. A nonphosphorylated mutant Cdx2 lacking the 4S motif (4S>A) exhibited reduced polyubiquitination upon proteasome inhibition and increased stability compared to wild-type Cdx2. In addition, we found that this mutant was less efficient to suppress colony formation than wild-type Cdx2. Thus, our data highlight a novel post-translational mechanism controlling Cdx2 degradation via phosphorylation and polyubiquitination, which may be of importance for intestinal development and cancer.

MEIS homeobox genes in neuroblastoma

The common pediatric tumor neuroblastoma originates from primitive neural crest-derived precursor cells of the peripheral nervous system. Neuroblastoma especially affects very young children, and can already be present at birth. Its early onset and cellular origin predict the involvement of developmental control genes in neuroblastoma etiology. These genes are indispensable for the tight regulation of normal embryonic development but as a consequence cause cancer and congenital diseases upon mutation or aberrant expression. To date however, the connotation of these genes in neuroblastoma pathogenesis is scant. This review recapitulates data on the MEIS homeobox control genes in cancer and focuses on neuroblastoma.

CALM-AF10+ T-ALL expression profiles are characterized by overexpression of HOXA and BMI1 oncogenes

The t(10;11)(p13;q14-21) is found in T-ALL and acute myeloid leukemia and fuses CALM (Clathrin-Assembly protein-like Lymphoid-Myeloid leukaemia gene) to AF10. In order to gain insight into the transcriptional consequences of this fusion, microarray-based comparison of CALM-AF10+ vs CALM-AF10- T-ALL was performed. This analysis showed upregulation of HOXA5, HOXA9, HOXA10 and BMI1 in the CALM-AF10+ cases. Microarray results were validated by quantitative RT-PCR on an independent group of T-ALL and compared to mixed lineage leukemia-translocated acute leukemias (MLL-t AL). The overexpression of HOXA genes was associated with overexpression of its cofactor MEIS1 in CALM-AF10+ T-ALL, reaching levels of expression similar to those observed in MLL-t AL. Consequently, CALM-AF10+ T-ALL and MLL-t AL share a specific HOXA overexpression, indicating they activate common oncogenic pathways. In addition, BMI1, located close to AF10 breakpoint, was overexpressed only in CALM-AF10+ T-ALL and not in MLL-t AL. BMI1 controls cellular proliferation through suppression of the tumor suppressors encoded by the CDKN2A locus. This locus, often deleted in T-ALL, was conserved in CALM-AF10+ T-ALL. This suggests that decreased CDKN2A activity, as a result of BMI1 overexpression, contributes to leukemogenesis in CALM-AF10+ T-ALL. We propose to define a HOXA+ leukemia group composed of at least MLL-t, CALM-AF10 and HOXA-t AL, which may benefit from adapted management.

Homeobox gene expression in cancer: insights from developmental regulation and deregulation

Homeobox genes encode transcription factors that play essential roles in controlling cell growth and differentiation during embryonic development. Many homeobox genes are aberrantly expressed in a wide variety of solid tumours, and their deregulation appears to enhance cell survival and proliferation and to inhibit differentiation. In hematologic malignancies, deregulated homeobox genes profoundly perturb self-renewal and proliferation of hematopoietic stem cells and progenitors. It is increasingly recognised that solid tumours, like hematologic malignancies, could arise from cancer stem cells, and that targeting these cells could be the most effective means of inhibiting tumour progression and disease recurrence. Studying the biological effects and mechanisms of homeobox genes in cancers could provide valuable insights into identifying cancer stem cells and targeting the self-renewal pathways in these cell populations.

A microarray model system identifies potential new target genes of the proto-oncogene HOX11

HOX11 is a homeobox gene originally identified at a chromosomal breakpoint in T-cell acute lymphoblastic leukemia (T-ALL). It is one of the most frequently deregulated genes in T-ALL, although the precise role of HOX11 in leukemogenesis as well as in normal development remains obscure. To gain more insight into the functional role of HOX11, we utilized a microarray model system to characterize the gene expression network that it directs. Using one of our T-ALL cell lines that had been stably transfected to express HOX11 and high-density oligonucleotide HG-U95A arrays, we identified a large number of differentially expressed genes in response to the enforced expression of HOX11. We focused on examining genes found to be up-regulated according to the microarray analysis and selected three putative target genes, NFKB2, SMARCD3, and NR4A3, for further investigation. We could not only confirm the up-regulation of NR4A3 by an independent method in all clones expressing HOX11, but luciferase reporter assays demonstrated that the effect that HOX11 exerted on the proximal promoter of NR4A3 was dependent on the presence of an intact homeodomain, providing support for the idea that HOX11 manifests its regulatory function via its action as a transcription factor.

Homeobox D10 Induces Phenotypic Reversion of Breast Tumor Cells in a Three-Dimensional Culture Model

Homeobox (Hox) genes are master regulatory genes that direct organogenesis and maintain differentiated tissue function. We previously reported that HoxD10 helps to maintain a quiescent, differentiated phenotype in endothelial cells by suppressing expression of genes involved in remodeling the extracellular matrix and cell migration. Here we investigated whether HoxD10 could also promote or maintain a differentiated phenotype in epithelial cells. We observed that HoxD10 expression is progressively reduced in epithelial cells as malignancy increases in both breast and endometrial tumors. Retroviral gene transfer to restore expression of HoxD10 in the malignant breast tumor cells MDA-MB-231 significantly impaired migration, and when these cells were cultured in a three-dimensional laminin-rich basement membrane (3DlrBM) model, they formed polarized, acinar structures. This phenotypic reversion was accompanied by decreased alpha3 integrin expression and reduced proliferation. Importantly, expression of HoxD10 in the MDA-MB-231 cells inhibited their ability to form tumors in mouse xenografts. Taken together, our results suggest that HoxD10 has tumor-suppressive functions for mammary epithelial cells.

HOXB4 enforces equivalent fates of ES-cell-derived and adult hematopoietic cells

Genetic manipulation of hematopoietic stem and progenitor cells is an important tool for experimental and clinical applied hematology. However, techniques that allow for gene targeting, subsequent in vitro selection, and expansion of genetically defined clones are available only for ES cells. Such molecularly defined and, hence, "safe" clones would be highly desirable for somatic gene therapy. Here, we demonstrate that in vitro differentiated ES cells completely recapitulate the growth and differentiation properties of adult bone marrow cells, in vitro and in vivo, when ectopically expressing HOXB4. Myeloid development was enforced and (T) lymphoid development suppressed over a wide range of expression levels, whereas only high expression levels of the transcription factor were detrimental for erythroid development. This indicates a close association between the amounts of ectopic HOXB4 present within a progenitor cell and and the decision to self renew or differentiate. Because HOXB4 mediates similar fates of ES-derived and bone marrow hematopoietic stem cells, the primitive embryonic cells can be considered a promising alternative for investigating hematopoietic reconstitution, in vivo, based on well defined clones. Provided that HOXB4 levels are kept within a certain therapeutic window, ES cells also carry the potential of efficient and safe somatic gene therapy.

Transcriptional programs following genetic alterations in p53, INK4A, and H-Ras genes along defined stages of malignant transformation

The difficulty to dissect a complex phenotype of established malignant cells to several critical transcriptional programs greatly impedes our understanding of the malignant transformation. The genetic elements required to transform some primary human cells to a tumorigenic state were described in several recent studies. We took the advantage of the global genomic profiling approach and tried to go one step further in the dissection of the transformation network. We sought to identify the genetic signatures and key target genes, which underlie the genetic alterations in p53, Ras, INK4A locus, and telomerase, introduced in a stepwise manner into primary human fibroblasts. Here, we show that these are the minimally required genetic alterations for sarcomagenesis in vivo. A genome-wide expression profiling identified distinct genetic signatures corresponding to the genetic alterations listed above. Most importantly, unique transformation hallmarks, such as differentiation block, aberrant mitotic progression, increased angiogenesis, and invasiveness, were identified and coupled with genetic signatures assigned for the genetic alterations in the p53, INK4A locus, and H-Ras, respectively. Furthermore, a transcriptional program that defines the cellular response to p53 inactivation was an excellent predictor of metastasis development and bad prognosis in breast cancer patients. Deciphering these transformation fingerprints, which are affected by the most common oncogenic mutations, provides considerable insight into regulatory circuits controlling malignant transformation and will hopefully open new avenues for rational therapeutic decisions.

Histone deacetylase activity is essential for the expression of HoxA9 and for endothelial commitment of progenitor cells

The regulation of acetylation is central for the epigenetic control of lineage-specific gene expression and determines cell fate decisions. We provide evidence that the inhibition of histone deacetylases (HDACs) blocks the endothelial differentiation of adult progenitor cells. To define the mechanisms by which HDAC inhibition prevents endothelial differentiation, we determined the expression of homeobox transcription factors and demonstrated that HoxA9 expression is down-regulated by HDAC inhibitors. The causal involvement of HoxA9 in the endothelial differentiation of adult progenitor cells is supported by the finding that HoxA9 overexpression partially rescued the endothelial differentiation blockade induced by HDAC inhibitors. Knockdown and overexpression studies revealed that HoxA9 acts as a master switch to regulate the expression of prototypical endothelial-committed genes such as endothelial nitric oxide synthase, VEGF-R₂, and VE-cadherin, and mediates the shear stress–induced maturation of endothelial cells. Consistently, HoxA9-deficient mice exhibited lower numbers of endothelial progenitor cells and showed an impaired postnatal neovascularization capacity after the induction of ischemia. Thus, HoxA9 is regulated by HDACs and is critical for postnatal neovascularization.

Gene amplification is a mechanism of Six1 overexpression in breast cancer

The Six1 homeoprotein plays a critical role in expanding progenitor populations during normal development via its stimulation of proliferation and inhibition of apoptosis. Overexpression of Six1 is observed in several tumor types, suggesting that when expressed out of context, Six1 may contribute to tumorigenesis by reinstating properties normally conveyed on developing cells. Indeed, Six1 contributes to tumor cell proliferation both in breast cancer and in rhabdomyosarcomas, in which it is also implicated in metastasis. Whereas Six1 overexpression has been reported in several tumor types, the mechanism responsible for its overexpression has not previously been examined. Here we show that a change in gene dosage may contribute to Six1 mRNA overexpression. Significant Six1 gene amplification and overrepresentation occurs in numerous breast cancer cell lines as compared with normal mammary epithelial cells, and the changes in gene dosage correlate with increased Six1 mRNA levels. Of 214 human infiltrating ductal breast carcinomas examined for Six1 gene dosage, 4.7% show Six1 amplification/overrepresentation, and tumors that exhibit an increase in Six1 gene dosage overexpress Six1 mRNA. These data implicate Six1 gene amplification/overrepresentation as a mechanism of Six1 mRNA overexpression in human breast cancer.

Expression of HOXB2, a retinoic acid signaling target in pancreatic cancer and pancreatic intraepithelial neoplasia

PURPOSE

Despite significant progress in understanding the molecular pathology of pancreatic cancer and its precursor lesion: pancreatic intraepithelial neoplasia (PanIN), there remain no molecules with proven clinical utility as prognostic or therapeutic markers. Here, we used oligonucleotide microarrays to interrogate mRNA expression of pancreatic cancer tissue and normal pancreas to identify novel molecular pathways dysregulated in the development and progression of pancreatic cancer.

EXPERIMENTAL DESIGN

RNA was hybridized to Affymetrix Genechip HG-U133 oligonucleotide microarrays. A relational database integrating data from publicly available resources was created to identify candidate genes potentially relevant to pancreatic cancer. The protein expression of one candidate, homeobox B2 (HOXB2), in PanIN and pancreatic cancer was assessed using immunohistochemistry.

RESULTS

We identified aberrant expression of several components of the retinoic acid (RA) signaling pathway (RARalpha, MUC4, Id-1, MMP9, uPAR, HB-EGF, HOXB6, and HOXB2), many of which are known to be aberrantly expressed in pancreatic cancer and PanIN. HOXB2, a downstream target of RA, was up-regulated 6.7-fold in pancreatic cancer compared with normal pancreas. Immunohistochemistry revealed ectopic expression of HOXB2 in 15% of early PanIN lesions and 48 of 128 (38%) pancreatic cancer specimens. Expression of HOXB2 was associated with nonresectable tumors and was an independent predictor of poor survival in resected tumors.

CONCLUSIONS

We identified aberrant expression of RA signaling components in pancreatic cancer, including HOXB2, which was expressed in a proportion of PanIN lesions. Ectopic expression of HOXB2 was associated with a poor prognosis for all patients with pancreatic cancer and was an independent predictor of survival in patients who underwent resection.

Tectorigenin and other phytochemicals extracted from leopard lily Belamcanda chinensis affect new and established targets for therapies in prostate cancer

Isoflavones have been shown to exert antiproliferative effects on cancer cells by steroid receptor signaling. In this study, we demonstrate the potential of plant constituents extracted from Belamcanda chinensis as anticancer drugs, which regulate the aberrant expression of genes relevant in proliferation, invasion, immortalization and apoptosis. LNCaP cells were treated with B.chinensis extract, tectorigenin or other isoflavones and mRNA expression was quantified by using real time RT-PCR. In addition, ELISA, TRAP assays and western blots were used to measure protein expression or activity. Male nude mice (n=18) were injected subcutaneously with LNCaP cells and were fed with extracts from B.chinensis, and tumor development was monitored versus a control animal group (n=18). Tectorigenin and several other phytochemicals downregulated PDEF, PSA and IGF-1 receptor mRNA expression in vitro. Furthermore, PSA secretion and IGF-1 receptor protein expression were diminished, and hTERT mRNA expression and telomerase activity decreased after tectorigenin treatments. However, TIMP-3 mRNA was upregulated on tectorigenin treatment. Growth of subcutaneous tumors in nude mice was delayed and diminished in animals fed with extracts from B.chinensis. The downregulation of PDEF, PSA, hTERT and IGF-1 receptor gene expression by tectorigenin demonstrates the antiproliferative potential of these agents. The upregulation of TIMP-3 gene expression indicates a pro-apoptotic function of the drug and a reduction of the invasiveness of tumors. The animal experiments demonstrate that B.chinensis markedly inhibited the development of tumors in vivo. Thus, these compounds may be useful for the prevention or treatment of human prostate cancer.

Lineage infidelity of epithelial ovarian cancers is controlled by HOX genes that specify regional identity in the reproductive tract

Although epithelial ovarian cancers (EOCs) have been thought to arise from the simple epithelium lining the ovarian surface or inclusion cysts, the major subtypes of EOCs show morphologic features that resemble those of the müllerian duct-derived epithelia of the reproductive tract. We found that HOX genes, which normally regulate mullerian duct differentiation, are not expressed in normal ovarian surface epithelium (OSE), but are expressed in different EOC subtypes according to the pattern of mullerian-like differentiation of these cancers. Ectopic expression of Hoxa9 in tumorigenic mouse OSE cells gave rise to papillary tumors resembling serous EOCs. In contrast, Hoxa10 and Hoxa11 induced morphogenesis of endometrioid-like and mucinous-like EOCs, respectively. Hoxa7 showed no lineage specificity, but promoted the abilities of Hoxa9, Hoxa10 and Hoxa11 to induce differentiation along their respective pathways. Therefore, inappropriate activation of a molecular program that controls patterning of the reproductive tract could explain the morphologic heterogeneity of EOCs and their assumption of müllerian-like features.

Usefulness of CDX2 and TTF-1 in differentiating gastrointestinal from pulmonary carcinoids

Carcinoids of different organs appear morphologically indistinguishable. We studied the usefulness of differential expression of CDX2 and thyroid transcription factor-1 (TTF-1) in 78 gastrointestinal and pulmonary carcinoids and their metastases (n = 10). CDX2 staining of gastric biopsy specimens with neuroendocrine hyperplasia (n = 11) and various gastritides (n = 10) was also performed. All ileal (6/6 [100%]), 6 (86%) of 7 appendiceal, 3 (75%) of 4 duodenal, 1 (50%) of 2 ampullary, 12 (33%) of 18 rectal, 6 (30%) of 20 pancreatic, and 1 (17%) of 6 gastric carcinoids expressed CDX2 with variable intensity; none of the pulmonary carcinoids stained. Of 15 pulmonary carcinoids, 8 (53%) stained with TTF-1, but none of the gastrointestinal carcinoids did. CDX2 and TTF-1 staining profiles of primary and metastatic carcinoids were similar. CDX2+ gastric endocrine cells had a distribution similar to that of gastrin and enterochromaffin cells but not enterochromaffin-like cells. Our results suggest that CDX2 and TTF-1 have high specificity for gastrointestinal and pulmonary carcinoids, respectively.

The homeobox gene Gax inhibits angiogenesis through inhibition of nuclear factor-kappaB-dependent endothelial cell gene expression

The growth and metastasis of tumors are heavily dependent on angiogenesis, but much of the transcriptional regulation of vascular endothelial cell gene expression responsible for angiogenesis remains to be elucidated. The homeobox gene Gax is expressed in vascular endothelial cells and inhibits proliferation and tube formation in vitro. We hypothesized that Gax is a negative transcriptional regulator of the endothelial cell angiogenic phenotype and studied its regulation and activity in vascular endothelial cells. Several proangiogenic factors caused a rapid down-regulation of Gax mRNA in human vascular endothelial cells, as did conditioned media from breast cancer cell lines. In addition, Gax expression using a replication-deficient adenoviral vector inhibited human umbilical vein endothelial cell migration toward proangiogenic factors in vitro and inhibited angiogenesis in vivo in Matrigel plugs. To identify putative downstream targets of Gax, we examined changes in global gene expression in endothelial cells due to Gax activity. Gax expression resulted in changes in global gene expression consistent with a quiescent, nonangiogenic phenotype, with increased expression of cyclin kinase inhibitors and decreased expression of genes implicated in endothelial cell activation and angiogenesis. Further analysis revealed that Gax down-regulated numerous nuclear factor-kappaB (NF-kappaB) target genes and decreased the binding of NF-kappaB to its target sequence in electrophoretic mobility shift assays. To our knowledge, Gax is the first homeobox gene described that inhibits NF-kappaB activity in vascular endothelial cells. Because NF-kappaB has been implicated in endothelial cell activation and angiogenesis, the down-regulation of NF-kappaB-dependent genes by Gax suggests one potential mechanism by which Gax inhibits the angiogenic phenotype.

HOXA genes are included in genetic and biologic networks defining human acute T-cell leukemia (T-ALL)

Using a combination of molecular cytogenetic and large-scale expression analysis in human T-cell acute lymphoblastic leukemias (T-ALLs), we identified and characterized a new recurrent chromosomal translocation, targeting the major homeobox gene cluster HOXA and the TCRB locus. Real-time quantitative polymerase chain reaction (RQ-PCR) analysis showed that the expression of the whole HOXA gene cluster was dramatically dysregulated in the HOXA-rearranged cases, and also in MLL and CALM-AF10-related T-ALL cases, strongly suggesting that HOXA genes are oncogenic in these leukemias. Inclusion of HOXA-translocated cases in a general molecular portrait of 92 T-ALLs based on large-scale expression analysis shows that this rearrangement defines a new homogeneous subgroup, which shares common biologic networks with the TLX1- and TLX3-related cases. Because T-ALLs derive from T-cell progenitors, expression profiles of the distinct T-ALL subgroups were analyzed with respect to those of normal human thymic subpopulations. Inappropriate use or perturbation of specific molecular networks involved in thymic differentiation was detected. Moreover, we found a significant association between T-ALL oncogenic subgroups and ectopic expression of a limited set of genes, including several developmental genes, namely HOXA, TLX1, TLX3, NKX3-1, SIX6, and TFAP2C. These data strongly support the view that the abnormal expression of developmental genes, including the prototypical homeobox genes HOXA, is critical in T-ALL oncogenesis.

Identification of transcriptional targets of HOXA5

The homeobox gene HOXA5 encodes a transcription factor that has been shown to play important roles in embryogenesis, hematopoiesis, and tumorigenesis. In order to decipher downstream signaling pathways of HOXA5, we utilized oligonucleotide microarray analysis to identify genes that are differentially expressed in HOXA5-induced cells compared with uninduced cells. Comparative analysis of gene expression changes after 9 h of HOXA5 induction in Hs578T breast cancer cells identified 306 genes whose expression was modulated at least 2-fold. Ten of these 306 genes were also up-regulated by at least 2-fold at 6 h post-induction. The expression of all of these 10 genes was confirmed by semiquantitative reverse transcription-PCR. Among these 10 genes, which are most likely to be direct targets of HOXA5, we initiated an investigation into the pleiotrophin gene by first cloning its promoter. Transient transfection assays indicated that HOXA5 can specifically activate the pleiotrophin promoter. Promoter deletion, chromatin immunoprecipitation assay, and gel-shift assays were performed to show that HOXA5 can directly bind to one binding site on the pleiotrophin promoter. These data strongly suggest that microarray analysis can successfully identify many potential direct downstream genes of HOXA5. Further functional analysis of these targets will allow us to better understand the diverse functions of HOXA5 in embryonic development and tumorigenesis.

The pathophysiology of HOX genes and their role in cancer

The HOM-C clustered prototype homeobox genes of Drosophila, and their counterparts, the HOX genes in humans, are highly conserved at the genomic level. These master regulators of development continue to be expressed throughout adulthood in various tissues and organs. The physiological and patho-physiological functions of this network of genes are being avidly pursued within the scientific community, but defined roles for them remain elusive. The order of expression of HOX genes within a cluster is co-ordinated during development, so that the 3' genes are expressed more anteriorly and earlier than the 5' genes. Mutations in HOXA13 and HOXD13 are associated with disorders of limb formation such as hand-foot-genital syndrome (HFGS), synpolydactyly (SPD), and brachydactyly. Haematopoietic progenitors express HOX genes in a pattern characteristic of the lineage and stage of differentiation of the cells. In leukaemia, dysregulated HOX gene expression can occur due to chromosomal translocations involving upstream regulators such as the MLL gene, or the fusion of a HOX gene to another gene such as the nucleoporin, NUP98. Recent investigations of HOX gene expression in leukaemia are providing important insights into disease classification and prediction of clinical outcome. Whereas the oncogenic potential of certain HOX genes in leukaemia has already been defined, their role in other neoplasms is currently being studied. Progress has been hampered by the experimental approach used in many studies in which the expression of small subsets of HOX genes was analysed, and complicated by the functional redundancy implicit in the HOX gene system. Attempts to elucidate the function of HOX genes in malignant transformation will be enhanced by a better understanding of their upstream regulators and downstream target genes.

Loss of HOXC6 expression induces apoptosis in prostate cancer cells

We have performed whole genome expression profiling of 28 patient prostate tumor samples and 12 normal prostate samples and identified 55 upregulated and 60 downregulated genes significantly changed in prostate tumor samples compared to normal prostate tissues. Among the members of the upregulated gene set was the developmental transcription factor Homeobox C6 (HOXC6). Silencing of HOXC6 expression using small-interfering RNA (siRNA) resulted in decreased proliferation rates for both androgen-dependent LnCaP cells and the LnCaP-derived androgen-independent C4-2 cell line. Flow cytometry and immunoblotting for the caspase-cleaved form of poly-ADP ribose polymerase (PARP) determined that the decrease in cell numbers was due to increased apoptosis. To validate the specificity of the siRNA-induced apoptosis, LnCaP cells were cotransfected with siRNA specific to the HOXC6 3'UTR and a mammalian expression vector containing the HOXC6 open reading frame, but lacking the 3'UTR. Overexpression of HOXC6 rescued the LnCaP cells from HOXC6 siRNA-induced apoptosis, and increased growth of control GFP siRNA-transfected cells. Expression profiling of HOXC6 siRNA transfections and HOXC6 overexpression identified neutral endopeptidase (NEP) and insulin-like growth factor binding protein-3 (IGFBP-3) as potential proapoptotic repression targets of HOXC6. Our data suggest that HOXC6 may be a novel potential therapeutic target for prostate cancer.

The identification of Hoxc8 target genes

Hox genes encode transcription factors that control spatial patterning during embryogenesis. To date, downstream targets of Hox genes have proven difficult to identify. Here, we describe studies designed to identify target genes under the control of the murine transcription factor Hoxc8. We used a mouse 16,463 gene oligonucleotide microarray to identify mRNAs whose expression was altered by the overexpression of Hoxc8 in C57BL/6J mouse embryo fibroblasts (MEF) in cell culture (in vitro). We identified a total of 34 genes whose expression was changed by 2-fold or greater: 16 genes were up-regulated, and 18 genes were down-regulated. The majority of genes encoded proteins involved in critical biological processes, such as cell adhesion, migration, metabolism, apoptosis, and tumorigenesis. Two genes showed high levels of regulation: (i) secreted phosphoprotein 1 (Spp1), also known as osteopontin (OPN), was down-regulated 4.8-fold, and (ii) frizzled homolog 2 (Drosophila) (Fzd2) was up-regulated 4.4-fold. Chromatin immunoprecipitation (ChIP) analysis confirmed the direct interaction between the OPN promoter and Hoxc8 protein in vivo, supporting the view that OPN is a direct transcriptional target of Hoxc8.

Homeobox Msx1 Interacts with p53 Tumor Suppressor and Inhibits Tumor Growth by Inducing Apoptosis

The stability of wild-type p53 is critical for its apoptotic function. In some cancers, wild-type p53 is inactivated by interaction with viral and cellular proteins, and restoration of its activity has therapeutic potential. Here, we identify homeobox Msx1 as a p53-interacting protein and show its novel function as a p53 regulator. Overexpression of homeobox Msx1 induced apoptosis of cancer cells harboring nonfunctional wild-type p53 and suppressed growth of human tumor xenografts in nude mice. The homeodomain of Msx1 functions as a protein-protein interacting motif rather than a DNA-binding domain and is essential for stabilization, nuclear accumulation, and apoptotic function of wild-type p53. The identification of a novel function of Msx1 as a p53 regulator may open new avenues for developing improved molecular therapies for tumors with a nonmutational p53 inactivation mechanism.

Expression of 11 HOX Genes Is Deregulated in Esophageal Squamous Cell Carcinoma

Purpose: HOX genes are vital for all aspects of mammalian growth and differentiation, and recent data have shown that their deregulated expression is related to carcinogenesis. To date, there has been no systemic study on expression of HOX genes in esophageal carcinoma. We investigated the expression pattern of 39 known HOX genes in cancerous and noncancerous tissue from 36 patients with esophageal squamous cell carcinoma to determine whether their expression is altered in esophageal cancer.

Experimental Design: Thirty-six patients with resectable esophageal squamous cell carcinoma (ESCC) were enrolled in this study. Specific primers were designed for each of 39 HOX genes, and reverse transcription-PCR was done in cancerous and noncancerous samples of these 36 patients. Furthermore, the expression of HOXA9 protein was subjected to Western blot analysis in all 36 paired tissue samples.

Results: Eight of 39 HOX genes were expressed in cancerous but not in noncancerous tissue. Five of 39 HOX genes were expressed both in cancerous and noncancerous tissue. Of the latter, expression of HOXA7, HOXA9, and HOXC6 was significantly higher in cancerous tissue (P &lt; 0.05). The remaining 26 HOX genes were not detected in either types of tissue. HOXA9 protein was expressed in both kinds of tissue (cancer tissue versus noncancerous mucosa: 0.34 ± 0.32 versus 0.24 ± 0.27, P = 0.121).

Conclusions: This is the first comprehensive survey of 39 HOX gene expression in ESCC and noncancerous mucosa. Five of the 39 HOX genes were expressed in both types of tissue indicating their possible role in maintaining normal structure and function of adult esophageal mucosa. Eleven of the 39 HOX genes were deregulated in cancer tissue. These genes possibly participate in the carcinogenesis of ESCC.

Identification of a new target region by loss of heterozygosity at 5p15.33 in sporadic gastric carcinomas: genotype and phenotype related

Chromosome 5p, especially 5p15, involves in several cancers. To investigate its role in gastric cancer, we analyzed 46 intestinal-type and 34 diffuse-type gastric cancers by Loss of heterozygosity (LOH). We found a high frequent LOH at 5p15.33, and identified a minimal 2.7 cM candidate region of tumor suppressor gene, encompassing four loci (D5S417, D5S2849, D5S1492 and D5S2088). In total 80 cases, the highest LOH occurs at D5S2849 (35.19%). In intestinal-type cases, the highest LOH frequency is 50%, whereas in diffuse-type cases, the highest is only 16.67%. By statistical analysis we also observed an obvious genotype-phenotype correlation on 5p15.3 (P<0.01).

CDX-2 Homeobox Gene Product Expression in Neuroendocrine Tumors

CDX-2 is a homeobox gene product essential for intestinal development and differentiation. It can be used as a specific marker of colorectal adenocarcinomas and other tumors with intestinal differentiation, but little is known about its expression in endocrine and neuroendocrine (NE) cells and NE primary and metastatic tumors. Using the Cdx-2-88 monoclonal antibody, we evaluated CDX-2 expression in routine samples of 20 normal endocrine/NE tissues and of 299 samples of well-differentiated NE tumors (WDNET) and high-grade NE carcinomas (NEC) from different sites. For 17 cases, we examined primary and corresponding metastatic lesions. We also examined 8 cytologic samples of liver metastases derived from 4 ileal WDNETs, 1 lung WDNET, and 3 pancreatic endocrine tumors. CDX-2 mRNA expression with RT-PCR technique on frozen material was evaluated in 5 WDNETs. CDX-2 was expressed in normal NE cells of the intestine and gastric fundus. High CDX-2 expression was seen in all ileal and appendiceal WDNET, while low levels were seen in WDNETs from stomach, duodenum, and rectum; no reactivity was seen in other WDNETs. Low levels of CDX-2 expression were seen in one third of nonfunctioning pancreatic WDNET where it was more frequently observed in cases with metastatic disease (P = 0.002). CDX-2 was identified in all cytologic specimens of metastatic ileal WDNETs. CDX-2 mRNA analysis confirmed immunohistochemical results. CDX-2 was expressed at high levels in 81% of intestinal NEC. Unexpectedly, variable levels of expression of CDX-2 were seen also in 39% of NEC of other sites, without any relation with the site of origin. This reactivity frequently overlapped TTF-1 expression, suggesting deregulated expression of homeobox genes in NEC. The restricted pattern of CDX-2 expression may have diagnostic value in the identification of the primary site of a metastatic WDNET. Conversely, a limited diagnostic role is suggested for CDX-2 in NEC because of its frequent expression in nongastrointestinal tumors.

Roles of the Nkx3.1 homeobox gene in prostate organogenesis and carcinogenesis

Although it is often presumed that the molecular pathways that underlie normal organogenesis are similar to those perturbed during carcinogenesis, few examples exist of tissue-specific regulatory genes that play central roles in both processes. In the case of the prostate gland, molecular genetic analyses have demonstrated that the Nkx3.1 homeobox gene plays an important role in normal differentiation of the prostatic epithelium and that its loss of function is an initiating event in prostate carcinogenesis. Thus, the Nkx3.1 homeobox gene provides a paradigm for understanding the relationship between normal differentiation and cancer, as well as a model for studying the roles of homeobox genes in these processes. Here, we review recent findings concerning the biological as well as biochemical function of this central regulator of prostate development and carcinogenesis.

Role of PLZF in melanoma progression

The promyelocytic leukemia zinc finger (PLZF) protein has been described as a transcriptional repressor of homeobox (HOX)-containing genes during embryogenesis. As we previously demonstrated a functional link between overexpression of HOXB7 and melanoma progression, we investigated the lack of PLZF as the possible cause of HOXB7 constitutive activation in these neoplastic cells. Accordingly, we found PLZF expression in melanocytes, but not in melanoma cells, a pattern inversely related to that of HOXB7. PLZF retroviral gene transduction was then performed in a panel of melanoma cell lines, and tumorigenicity was compared with that of empty vector-transduced control cell lines. Evaluation of in vitro migration, invasion and adhesion indicated that PLZF gene transduction induced a less malignant phenotype, as confirmed through in vivo studies performed in athymic nude mice. This reduced tumorigenicity was not coupled with HOXB7 repression. In order to find more about the molecular targets of PLZF, the gene expression profiles of PLZF- and empty vector-transduced A375 melanoma cells were analysed by Atlas Cancer macroarray. Among several genes modulated by PLZF enforced expression, of particular interest were integrin alphavbeta3, osteonectin/SPARC and matrix metalloprotease-9 that were downmodulated, and the tyrosinase-related protein-1 that was upregulated in all the analysed samples. This profile confirms the reduced tumorigenic phenotype with reversion to a more differentiated, melanocyte like, pattern, thus suggesting a suppressor role for PLZF in solid tumors. Moreover, these results indicate that PLZF and HOXB7 are functionally independent and that their coupled deregulation may account for most of the alterations described in melanomas.

Impairment of SHOX nuclear localization as a cause for Léri-Weill syndrome

We report the characterization of the nuclear localization signal (NLS) of the short stature homeobox gene SHOX. Mutations within the SHOX gene cause Léri-Weill dyschondrosteosis (LWD) and Langer mesomelic dysplasia (LD) as well as idiopathic short stature (ISS). Furthermore, haploinsufficiency of SHOX has also been implicated in Turner syndrome. SHOX has been shown to be a cell-type-specific transcriptional activator that localizes to the nucleus. The SHOX protein contains a central homeodomain that together with its transactivation domain regulates the transcription of its target sequences within the nucleus. The sequences for its nuclear localization have not been identified yet. Experimental characterization of SHOX-NLS by deletion mapping identified a non-classic type basic signal, AKCRK, in the recognition helix of the homeodomain. Fusion of this stretch of five amino acids to a cytoplasmic reporter protein resulted in its nuclear translocation. Functional analysis of a missense mutation R173C (C517T) affecting the identified SHOX-NLS in two families with LWS and LD showed that the mutated SHOX protein is unable to enter the nucleus. Conversely, we can demonstrate that insertion of the identified signal adjacent to the mutant site can restore its nuclear translocation. These results establish impairment of nuclear localization as a mechanistic basis for SHOX-related diseases.

A two-gene expression ratio predicts clinical outcome in breast cancer patients treated with tamoxifen

Tamoxifen significantly reduces tumor recurrence in certain patients with early-stage estrogen receptor-positive breast cancer, but markers predictive of treatment failure have not been identified. Here, we generated gene expression profiles of hormone receptor-positive primary breast cancers in a set of 60 patients treated with adjuvant tamoxifen monotherapy. An expression signature predictive of disease-free survival was reduced to a two-gene ratio, HOXB13 versus IL17BR, which outperformed existing biomarkers. Ectopic expression of HOXB13 in MCF10A breast epithelial cells enhances motility and invasion in vitro, and its expression is increased in both preinvasive and invasive primary breast cancer. The HOXB13:IL17BR expression ratio may be useful for identifying patients appropriate for alternative therapeutic regimens in early-stage breast cancer.

Potential pathologic markers for prostate chemoprevention studies

The field of exploring potential biomarkers for prostate cancer prevention continues to expand rapidly. In addition to a limited scope of histologic alterations, mainly PIN, a growing array of promising technologies (eg, computer-assisted analysis), and molecules involved in cell-cycle regulations, angiogenesis, and structural and numerical chromosomal alterations are potential candidates for surrogate endpoint biomarkers for prevention trials. Before any these potential candidates are adopted, however, the technical, interpretational, and validation requirements must be satisfied. More important, it is crucial to demonstrate that modulation of the frequency of the biomarker decreases the rate of cancer development.

Inhibition of telomerase activity and secretion of prostate specific antigen by silibinin in prostate cancer cells

PURPOSE

The androgen sensitive prostate cancer cell line LNCaP is strongly positive for dihydrotestosterone (DHT) dependent telomerase activity, which is an important factor in cellular immortality and carcinogenesis. In this study we determined the potential of silibinin as an anticancer drug that down-regulates telomerase activity and prostate specific antigen (PSA) together with the co-activator of the androgen receptor prostate epithelium specific Ets transcription factor.

MATERIALS AND METHODS

LNCaP cells were treated with various concentrations of silibinin in the presence or absence of 5alpha-DHT. We used real-time reverse transcriptase-polymerase chain reaction to quantify mRNA expression of PSA, prostate epithelium specific Ets transcription factor and the catalytic subunit of telomerase vs the housekeeping gene porphobilinogen deaminase with gene specific, dual labeled fluorescence probes. PSA secretion from LNCaP cells in conditioned medium was measured with an Elecsys System 2010 (Roche Diagnostics, Mannheim, Germany) and telomerase activity in extracts from LNCaP cells was measured with a TRAP (telomeric repeat amplification protocol) assay.

RESULTS

Silibinin down-regulated PSA mRNA expression and PSA secretion in conditioned medium. Simultaneous stimulation with silibinin and 10(-8) M DHT also resulted in PSA down-regulation, whereas DHT alone increased PSA secretion. Telomerase catalytic subunit mRNA decreased significantly after silibinin stimulation. Telomerase activity was down-regulated by silibinin and stimulated by DHT. The 2 agents in combination resulted in telomerase down-regulation.

CONCLUSIONS

The down-regulation of PSA by silibinin and its counteraction on DHT effects indicate that this compound can interact with the expression of genes that are regulated through the androgen receptor. Silibinin can also inhibit the telomerase activity that mediates cell immortality and carcinogenesis. The 2 effects underline the possible therapeutic use of silibinin as an antiproliferative agent in intervention for prostate cancer.

The Six1 homeoprotein stimulates tumorigenesis by reactivation of cyclin A1

Homeobox genes constitute a large family of transcription factors that are essential during normal development and are often dysregulated in cancer. However, the molecular mechanisms by which homeobox genes influence cancer remain largely unknown. Here we show that the tissue-restricted cyclin A1 is a transcriptional target of the Six1 homeoprotein. Both genes are expressed in the embryonic but not the terminally differentiated mammary gland, and Six1-knockout mice show a dramatic reduction of cyclin A1 in the embryonic mammary gland. In addition, both genes are reexpressed in breast cancers. Six1 overexpression increases cyclin A1 mRNA levels and activity, cell proliferation, and tumor volume, whereas Six1 down-regulation decreases cyclin A1 mRNA levels and proliferation. Overexpression of Six1 in wild-type mouse embryonic fibroblasts, but not in knockout variants lacking the cyclin A1 gene, induces cell proliferation. Furthermore, inhibition of cyclin A1 in Six1-overexpressing mammary carcinoma cells decreases proliferation. Together these results demonstrate that cyclin A1 is required for the proliferative effect of Six1. We conclude that Six1 overexpression reinstates an embryonic pathway of proliferation in breast cancer by up-regulating cyclin A1.

Expression of mesenchyme-specific gene HMGA2 in squamous cell carcinomas of the oral cavity

Carcinoma cells of epithelial origin are predisposed to acquire a fibroblastic feature during progression of neoplasm referred to as the epithelial-mesenchymal transition. HMGA2 is an architectural transcriptional factor that is expressed in the undifferentiated mesenchyme and initiates mesenchymal tumor formation. However, the biological consequence of the expression in the pathology of epithelial-type carcinomas is controversial. The present study was conducted to dissect the expression pattern in oral squamous cell carcinomas. HMGA2 was detected exclusively in carcinoma cell lines and tissues, but not in normal keratinocytes and gingival, by conventional reverse transcription-PCR. Quantitative real-time reverse transcription-PCR demonstrated 160-fold more HMGA2 expression in carcinoma tissues than in normal gingiva and 11-fold more HMGA2 expression in carcinoma cell lines than in normal keratinocytes. HMGA2 expression was observed by immunohistochemistry in 73.8% of 42 carcinomas and localized to the invasive front, where the cells exhibit the epithelial-mesenchymal transition. Fourteen patients who had been classified into a group without lymph node metastasis were positive for HMGA2 staining, and the disease recurred. Furthermore, carcinomas from all 23 patients who died of tumor recurrence stained for HMGA2, and HMGA2 staining was correlated to long-term survival of patients (P < 0.01). Multivariate risk factor analysis demonstrated that HMGA2 expression was an independent prognostic value for disease-specific overall survival (P < 0.01). These results suggest that HMGA2 contributes to the aggressiveness of carcinoma and that detection of HMGA2 expression is a useful predictive and prognostic tool in clinical management of oral carcinomas.

Msx-1 and Msx-2 in mammary gland development

Homeobox genes do not generally function alone to determine cell fate and morphogenesis. Rather it is the distinct combination of various members of the homeobox family of genes and their spatiotemporal patterns of expression that determine cell identity and function. Functional redundancy often makes it difficult to clearly discern the role of any one given homeobox gene. The roles that Msx1 and Msx2 play in branching morphogenesis of the mammary gland are only now becoming more evident. Many signaling pathways and transcription factors are implicated in how these homeobox genes correctly determine the morphological development of the gland. Overexpression of Msx1 and Msx2 may also be involved in tumorigenesis. Additional studies are needed to elucidate the roles of these genes in both breast development and cancer.

The cell-cycle regulator geminin inhibits Hox function through direct and polycomb-mediated interactions

Embryonic development is tightly controlled. The clustered genes of the Hox family of homeobox proteins play an important part in regulating this development and also proliferation. They specify embryonic structures along the body axis, and are associated with normal and malignant cell growth. The cell-cycle regulator geminin controls replication by binding to the licensing factor Cdt1, and is involved in neural differentiation. Here, we show that murine geminin associates transiently with members of the Hox-repressing polycomb complex, with the chromatin of Hox regulatory DNA elements and with Hox proteins. Gain- and loss-of-function experiments in the chick neural tube demonstrate that geminin modulates the anterior boundary of Hoxb9 transcription, which suggests a polycomb-like activity for geminin. The interaction between geminin and Hox proteins prevents Hox proteins from binding to DNA, inhibits Hox-dependent transcriptional activation of reporter and endogenous downstream target genes, and displaces Cdt1 from its complex with geminin. By establishing competitive regulation, geminin functions as a coordinator of developmental and proliferative control.

HOXA5-induced apoptosis in breast cancer cells is mediated by caspases 2 and 8

HOXA5 is a transcriptional factor whose expression is lost in more than 60% of breast carcinomas. Our previous work demonstrated that the overexpression of HOXA5 in MCF7 cells resulted in cell death through a p53-dependent apoptotic pathway. To determine whether p53-independent apoptotic pathways are involved in HOXA5-induced cell death, we engineered a p53-mutant breast cancer cell line, Hs578T, to inducibly express HOXA5. Induction of HOXA5 expression led to cell death with features typical of apoptosis within 24 h, and the expression levels of mutant p53 and its target genes either decreased or remained unchanged. To decipher apoptotic pathways, the HOXA5-expressing cells were treated with a variety of apoptotic inhibitors. Besides a general caspase inhibitor, caspase 2- and 8-specific inhibitors largely abolished HOXA5-induced apoptosis, whereas caspase 1-, 3-, 6-, and 9-specific inhibitors had no significant effects. Western blot analysis further confirmed that caspases 2 and 8 were activated after the induction of HOXA5 expression. Further, several small interfering RNAs which specifically silenced caspase 2 and caspase 8 expression significantly blocked HOXA5-induced apoptosis. HOXA5 expression could also sensitize cells to tumor necrosis factor alpha-induced apoptosis by at least 100-fold. These results indicate that expression of HOXA5 can induce apoptosis through an apoptotic mechanism mediated by caspases 2 and 8.