Mutation analysis of theHOX paralogous 4-13 genes in children with acute lymphoid malignancies: Identification of a novel germline mutation ofHOXD4 leading to a partial loss-of-function

Molecular implications of HOX genes targeting multiple signaling pathways in cancer

Homeobox (HOX) genes encode highly conserved homeotic transcription factors that play a crucial role in organogenesis and tissue homeostasis. Their deregulation impacts the function of several regulatory molecules contributing to tumor initiation and progression. A functional bridge exists between altered gene expression of individual HOX genes and tumorigenesis. This review focuses on how deregulation in the HOX-associated signaling pathways contributes to the metastatic progression in cancer. We discuss their functional significance, clinical implications and ascertain their role as a diagnostic and prognostic biomarker in the various cancer types. Besides, the mechanism of understanding the theoretical underpinning that affects HOX-mediated therapy resistance in cancers has been outlined. The knowledge gained shall pave the way for newer insights into the treatment of cancer.

Prognostic significance of HOXD4 protein expression in human ovarian cancers

Objectives

Ovarian cancer is the most common gynecological malignancy, ranking as the fifth leading cause of cancer-related deaths among females in the United States. Homeobox D4 (HOXD4) is a transcription factor belonging to the homeobox protein family, which plays a critical role in morphogenesis during embryo development. Here we aimed to study the HOXD4 expression in ovarian serous carcinoma (OSC) and determine its clinical significance.

Materials and Methods

Real-time quantitative PCR and immunohistochemistry targeting human OSC tissues and adjacent ovarian tissues were performed to correlate the patterns of HOXD4 expression with clinical characteristics and survival outcomes. Cell lines and nude mice were used for verifying the role of HOXD4 in OSC.

Results

HOXD4 protein was predominantly expressed in OSC tissues compared with nontumorous tissues. The correlation test demonstrated a significant correlation between HOXD4 with tumor FIGO stage. Univariate and multivariate analyses found that HOXD4 expression was associated with poorer overall survival. Furthermore, high expression of HOXD4 protein was observed in OSC cell lines in vitro. Finally, the oncogenic effect of HOXD4 was confirmed by cellular and xenograft experiments.

Conclusion

HOXD4 protein expression may be associated with a poorer prognosis in OSC. The unfavorable prognostic value of HOXD4 in malignancies and its underlying mechanism are worthy of further investigation.

The Role of HOX Transcription Factors in Cancer Predisposition and Progression

Homeobox (HOX) transcription factors, encoded by a subset of homeodomain superfamily genes, play pivotal roles in many aspects of cellular physiology, embryonic development, and tissue homeostasis. Findings over the past decade have revealed that mutations in HOX genes can lead to increased cancer predisposition, and HOX genes might mediate the effect of many other cancer susceptibility factors by recognizing or executing altered genetic information. Remarkably, several lines of evidence highlight the interplays between HOX transcription factors and cancer risk loci discovered by genome-wide association studies, thereby gaining molecular and biological insight into cancer etiology. In addition, deregulated HOX gene expression impacts various aspects of cancer progression, including tumor angiogenesis, cell autophagy, proliferation, apoptosis, tumor cell migration, and metabolism. In this review, we will discuss the fundamental roles of HOX genes in cancer susceptibility and progression, highlighting multiple molecular mechanisms of HOX involved gene misregulation, as well as their potential implications in clinical practice.

HOX genes: Major actors in resistance to selective endocrine response modifiers

Long term treatment with therapies aimed at blocking the estrogen- (ER) or androgen receptor (AR) action often leads to the development of resistance to selective modulators of the estrogen receptor (SERMs) in ERα-positive breast cancer, or of the androgen receptor (SARMs) in AR-positive prostate cancer. Many underlying molecular events that confer resistance are known, but a unifying theme is yet to be revealed. Receptor tyrosine kinases (RTKs) such EGFR, ERBB2 and IGF1R are major mediators that can directly alter cellular response to the SERM, tamoxifen, but the mechanisms underlying increased expression of RTKs are not clear. A number of HOX genes and microRNAs and non-coding RNAs residing in the HOX cluster, have been identified as important independent predictors of endocrine resistant breast cancer. Recently, convincing evidence has accumulated that several members belonging to the four different HOX clusters contribute to endocrine therapy resistant breast cancer, but the mechanisms remain obscure. In this article, we have reviewed recent progress in understanding of the functioning of HOX genes and regulation of their expression by hormones. We also discuss, in particular, the contributions of several members of the HOX gene family to endocrine resistant breast cancer.

Identification of HOXD4 Mutations in Spinal Extradural Arachnoid Cyst

Spinal extradural arachnoid cyst (SEDAC) is a cyst in the spinal canal that protrudes into the epidural space from a defect in the dura mater and leads to neurological disturbances. We previously showed that familial SEDAC is caused by FOXC2 mutation; however, the causal gene of sporadic SEDAC has not been identified. To identify the causal gene of sporadic SEDAC, we performed whole exome sequencing for 12 subjects with sporadic SEDAC and identified heterozygous HOXD4 loss-of-function mutations in three subjects. HOXD4 haplo-insufficiency causes SEDAC and a transcriptional network containing HOXD4 and FOXC2 is involved in the development of the dura mater and the etiology of SEDAC.

Human HOX gene disorders

The Hox genes are an evolutionarily conserved family of genes, which encode a class of important transcription factors that function in numerous developmental processes. Following their initial discovery, a substantial amount of information has been gained regarding the roles Hox genes play in various physiologic and pathologic processes. These processes range from a central role in anterior-posterior patterning of the developing embryo to roles in oncogenesis that are yet to be fully elucidated. In vertebrates there are a total of 39 Hox genes divided into 4 separate clusters. Of these, mutations in 10 Hox genes have been found to cause human disorders with significant variation in their inheritance patterns, penetrance, expressivity and mechanism of pathogenesis. This review aims to describe the various phenotypes caused by germline mutation in these 10 Hox genes that cause a human phenotype, with specific emphasis paid to the genotypic and phenotypic differences between allelic disorders. As clinical whole exome and genome sequencing is increasingly utilized in the future, we predict that additional Hox gene mutations will likely be identified to cause distinct human phenotypes. As the known human phenotypes closely resemble gene-specific murine models, we also review the homozygous loss-of-function mouse phenotypes for the 29 Hox genes without a known human disease. This review will aid clinicians in identifying and caring for patients affected with a known Hox gene disorder and help recognize the potential for novel mutations in patients with phenotypes informed by mouse knockout studies.

Adaptive evolution of the Hox gene family for development in bats and dolphins

Bats and cetaceans (i.e., whales, dolphins, porpoises) are two kinds of mammals with unique locomotive styles and occupy novel niches. Bats are the only mammals capable of sustained flight in the sky, while cetaceans have returned to the aquatic environment and are specialized for swimming. Associated with these novel adaptations to their environment, various development changes have occurred to their body plans and associated structures. Given the importance of Hox genes in many aspects of embryonic development, we conducted an analysis of the coding regions of all Hox gene family members from bats (represented by Pteropus vampyrus, Pteropus alecto, Myotis lucifugus and Myotis davidii) and cetaceans (represented by Tursiops truncatus) for adaptive evolution using the available draft genome sequences. Differences in the selective pressures acting on many Hox genes in bats and cetaceans were found compared to other mammals. Positive selection, however, was not found to act on any of the Hox genes in the common ancestor of bats and only upon Hoxb9 in cetaceans. PCR amplification data from additional bat and cetacean species, and application of the branch-site test 2, showed that the Hoxb2 gene within bats had significant evidence of positive selection. Thus, our study, with genomic and newly sequenced Hox genes, identifies two candidate Hox genes that may be closely linked with developmental changes in bats and cetaceans, such as those associated with the pancreatic, neuronal, thymus shape and forelimb. In addition, the difference in our results from the genome-wide scan and newly sequenced data reveals that great care must be taken in interpreting results from draft genome data from a limited number of species, and deep genetic sampling of a particular clade is a powerful tool for generating complementary data to address this limitation.

Nuclear accumulation of an uncapped RNA produced by Drosha cleavage of a transcript encoding miR-10b and HOXD4

Patterning of the animal embryo's antero-posterior (AP) axis is dependent on spatially and temporally regulated Hox gene expression. The murine Hoxd4 gene has been proposed to harbour two promoters, an upstream promoter P2, and a downstream promoter P1, that lie 5.2 and 1.1 kilobase pairs (kb) upstream of the coding region respectively. The evolutionarily conserved microRNA-10b (miR-10b) gene lies in the Hoxd4 genomic locus in the intron separating the non-coding exons 4 and 5 of the P2 transcript and directly adjacent to the proposed P1 promoter. Hoxd4 transcription is regulated by a 3′ neural enhancer that harbours a retinoic acid response element (RARE). Here, we show that the expression profiles of Hoxd4 and miR-10b transcripts during neural differentiation of mouse embryonal carcinoma (EC) P19 cells are co-ordinately regulated, suggesting that both Hoxd4 and miR-10b expression is governed by the neural enhancer. Our observation that P1 transcripts are uncapped, together with the mapping of their 5′ ends, strongly suggests that they are generated by Drosha cleavage of P2 transcripts rather than by transcriptional initiation. This is supported by the colocalization of P1 and P2 transcripts to the same posterior expression domain in the mouse embryo. These uncapped P1 transcripts do not appear to possess an Internal Ribosomal Entry Site (IRES), but accumulate within multiple punctate bodies within the nucleus suggesting that they play a functional role. Finally, similar uncapped Drosha-cleaved P1-like transcripts originating from the paralogous Hoxb4/miR-10a locus were also identified. We propose that these transcripts may belong to a novel class of regulatory RNAs.

Polymorphisms in the HOXD4 gene are not associated with peak bone mineral density in Chinese nuclear families

AIM

To determine the associations between HOXD4 gene polymorphisms with peak bone mineral density (BMD) throughing measuring three tagging single nucleotide polymorphisms (tagSNPs), including rs1867863, rs13418078, and rs4972504, in HOXD4.

METHODS

Four hundred Chinese nuclear families with male offspring (1215 subjects) and 401 Chinese nuclear families with female offspring (1260 subjects) were recruited. BMD of the lumbar spine 1-4 (L1-4) and left proximal femur including total hip and femoral neck were measured by dual-energy X-ray absorptiometry. The quantitative transmission disequilibrium test (QTDT) was performed to investigate the association among the tagging SNPs, haplotypes and peak BMD.

RESULTS

Only the CC genotype was identified in rs13418078 in the Chinese population, unlike other populations. We failed to find significant within-family association among these SNPs, haplotypes and peak BMD at any bone site in either male- or female-offspring nuclear families.

CONCLUSION

The results suggest that genetic polymorphisms in HOXD4 may not be a major contributor to the observed variability in peak BMD in the lumbar spine and the hip in Chinese men and women.

Hox-D genes expression in pediatric low-grade gliomas: real-time-PCR study

HOX genes encode transcription factors, which play a key role in morphogenesis and cell differentiation during embryogenesis. Several observations indicate that a deregulated expression of these genes may result in tumor development and progression. Actually, several HOX genes are aberrantly expressed in many tumors and cell lines derived from them. Little is known about the expression of HOX genes in brain tumors. In the present work, we study the relative expression of HOX-D genes (D1, D3, D4, D8, D9, D10, D11, D12, D13) with real-time polymerase chain reaction in a group of 14 pediatric low-grade gliomas. We compare the HOX-D expression level of the 14 tumors with the average expression level of six non-neoplastic human brain tissues. HOX-D1 and HOX-D12 resulted over-expressed in neoplastic samples with respect to non-neoplastic brain parenchyma. Conversely, HOX-D3 was expressed at a lower level in gliomas with respect to non-neoplastic brain. HOX-D4, HOX-D11, and HOX-D13 were never expressed. HOX-D8, HOX-D9, and HOX-D10 were exceptionally expressed in non-neoplastic samples and irregularly expressed in tumors. The observation that all but three HOX-D genes studied are expressed with different pattern in neoplastic and non-neoplastic brain tissue may support the hypothesis that HOX-D genes play a role in the pathogenesis of pediatric low-grade gliomas.

HOXA10 mutations in congenital absence of uterus and vagina

OBJECTIVE

To analyze the HOXA10 genes in CAUV patients for mutations. Congenital absence of the uterus and vagina (CAUV) is the most extreme female reproductive tract developmental defect known. The HOXA10 gene is expressed in the developing and adult uterus. Female mice with loss-of-function Hoxa10 gene mutations have anteriorly directed homeotic transformations of the uterus. Because the HOXA10 gene is expressed in the embryonic paramesonephric (Müllerian) ducts, abnormally low expression by mutant HOXA10 genes might cause CAUV. This hypothesis was tested by analyzing the HOXA10 genes in CAUV patients for mutations.

DESIGN

Case-control study.

SETTING

Academic reproductive endocrinology and infertility practice.

PATIENT(S)

Blood samples were obtained from 26 patients with CAUV and 30 normal controls.

INTERVENTION(S)

DNA samples prepared from blood leukocytes were used as templates for polymerase chain reaction (PCR) amplification of DNA fragments from the HOXA10 gene. The gene fragments were tested for DNA sequence differences using denaturing gradient gel electrophoresis (DGGE).

MAIN OUTCOME MEASURE(S)

To detect DNA sequence differences between patients with CAUV and normal controls.

RESULT(S)

No DNA sequence differences were found in either patients with CAUV or normal controls in either of the two protein-coding exons of the HOXA10 gene.

CONCLUSION(S)

Because no HOXA10 gene mutations were found in 26 patients from 25 unrelated families, germ- line mutations in the HOXA10 gene are not a common cause of CAUV.