Novel gene fusion of COX6C at 8q22-23 to HMGIC at 12q15 in a uterine leiomyoma

A View on Uterine Leiomyoma Genesis through the Prism of Genetic, Epigenetic and Cellular Heterogeneity

Uterine leiomyomas (ULs), frequent benign tumours of the female reproductive tract, are associated with a range of symptoms and significant morbidity. Despite extensive research, there is no consensus on essential points of UL initiation and development. The main reason for this is a pronounced inter- and intratumoral heterogeneity resulting from diverse and complicated mechanisms underlying UL pathobiology. In this review, we comprehensively analyse risk and protective factors for UL development, UL cellular composition, hormonal and paracrine signalling, epigenetic regulation and genetic abnormalities. We conclude the need to carefully update the concept of UL genesis in light of the current data. Staying within the framework of the existing hypotheses, we introduce a possible timeline for UL development and the associated key events—from potential prerequisites to the beginning of UL formation and the onset of driver and passenger changes.

Neoplasia-associated Chromosome Translocations Resulting in Gene Truncation

Chromosomal translocations in cancer as well as benign neoplasias typically lead to the formation of fusion genes. Such genes may encode chimeric proteins when two protein-coding regions fuse in-frame, or they may result in deregulation of genes via promoter swapping or translocation of the gene into the vicinity of a highly active regulatory element. A less studied consequence of chromosomal translocations is the fusion of two breakpoint genes resulting in an out-of-frame chimera. The breaks then occur in one or both protein-coding regions forming a stop codon in the chimeric transcript shortly after the fusion point. Though the latter genetic events and mechanisms at first awoke little research interest, careful investigations have established them as neither rare nor inconsequential. In the present work, we review and discuss the truncation of genes in neoplastic cells resulting from chromosomal rearrangements, especially from seemingly balanced translocations.

Novel role of COX6c in the regulation of oxidative phosphorylation and diseases

Cytochrome c oxidase subunit VIc (COX6c) is one of the most important subunits of the terminal enzyme of the respiratory chain in mitochondria. Numerous studies have demonstrated that COX6c plays a critical role in the regulation of oxidative phosphorylation (OXPHOS) and energy production. The release of COX6c from the mitochondria may be a hallmark of the intrinsic apoptosis pathway. Moreover, The changes in COX6c expression are widespread in a variety of diseases and can be chosen as a potential biomarker for diagnosis and treatment. In light of its exclusive effects, we present the elaborate roles that COX6c plays in various diseases. In this review, we first introduced basic knowledge regarding COX6c and its functions in the OXPHOS and apoptosis pathways. Subsequently, we described the regulation of COX6c expression and activity in both positive and negative ways. Furthermore, we summarized the elaborate roles that COX6c plays in various diseases, including cardiovascular disease, kidney disease, brain injury, skeletal muscle injury, and tumors. This review highlights recent advances and provides a comprehensive summary of COX6c in the regulation of OXPHOS in multiple diseases and may be helpful for drug design and the prediction, diagnosis, treatment, and prognosis of diseases.

HMGA2: A Biomarker in Gynecologic Neoplasia

High Mobility Group A2 gene (HMGA2), an oncofetal protein, is normally expressed in fetal development and completely shuts down in almost all organs and tissue types during adulthood. It is upregulated or overexpressed again in certain mesenchymal neoplasms due to chromosomal translocations and in malignant epithelial tumors through transcription regulation. HMGA2 overexpression can either drive tumor development or promote the aggressiveness of tumor growth. Many gynecologic neoplasms, including uterine smooth muscle tumors and ovarian cancer, are associated with HMGA2 overexpression. In this article, we review recent developments in the study of HMGA2 and its expression as a potential biomarker for gynecologic neoplasms and clinic application.

High Mobility Group AT-Hook 2 (HMGA2) Oncogenicity in Mesenchymal and Epithelial Neoplasia

High mobility group AT-hook 2 (HMGA2) has been associated with increased cell proliferation and cell cycle dysregulation, leading to the ontogeny of varied tumor types and their metastatic potentials, a frequently used index of disease prognosis. In this review, we deepen our understanding of HMGA2 pathogenicity by exploring the mechanisms by which HMGA2 misexpression and ectopic expression induces mesenchymal and epithelial tumorigenesis respectively and distinguish the pathogenesis of benign from malignant mesenchymal tumors. Importantly, we highlight the regulatory role of let-7 microRNA family of tumor suppressors in determining HMGA2 misexpression events leading to tumor pathogenesis and focused on possible mechanisms by which HMGA2 could propagate lymphangioleiomyomatosis (LAM), benign mesenchymal tumors of the lungs. Lastly, we discuss potential therapeutic strategies for epithelial and mesenchymal tumorigenesis based on targeting the HMGA2 signaling pathway.

Detection and screening of chromosomal rearrangements in uterine leiomyomas by long-distance inverse PCR

Genome instability is a hallmark of many tumors and recently, next-generation sequencing methods have enabled analyses of tumor genomes at an unprecedented level. Studying rearrangement-prone chromosomal regions (putative "breakpoint hotspots") in detail, however, necessitates molecular assays that can detect de novo DNA fusions arising from these hotspots. Here we demonstrate the utility of a long-distance inverse PCR-based method for the detection and screening of de novo DNA rearrangements in uterine leiomyomas, one of the most common types of human neoplasm. This assay allows in principle any genomic region suspected of instability to be queried for DNA rearrangements originating there. No prior knowledge of the identity of the fusion partner chromosome is needed. We used this method to screen uterine leiomyomas for rearrangements at genomic locations known to be rearrangement-prone in this tumor type: upstream HMGA2 and within RAD51B. We identified a novel DNA rearrangement upstream of HMGA2 that had gone undetected in an earlier whole-genome sequencing study. In more than 30 additional uterine leiomyoma samples, not analyzed by whole-genome sequencing previously, no rearrangements were observed within the 1,107 bp and 1,996 bp assayed in the RAD51B and HMGA2 rearrangement hotspots. Our findings show that long-distance inverse PCR is a robust, sensitive, and cost-effective method for the detection and screening of DNA rearrangements from solid tumors that should be useful for many diagnostic applications.

Lymphovascular invasion and histologic grade are associated with specific genomic profiles in invasive carcinomas of the breast

Lymphovascular invasion (LVI) and histologic grade are clinical parameters of high prognostic value in breast cancer and indicate the level of tumor aggressiveness. Many studies have focused on the association of breast cancer subtypes with gene expression and chromosomal profiles, but considerably less genomic information is available regarding traditional prognostic factors such as histologic grade and LVI. We studied by array-CGH a group of 57 invasive ductal carcinomas of the breast to outline the DNA copy number aberration (CNA) profile linked to high histologic grades and LVI. Selected CNAs were validated using real-time quantitative PCR (qPCR). Furthermore, gene expression analysis was performed in a subset of 32 of these tumors, and findings were integrated with array-CGH data. Our findings indicated an accumulation of genomic alterations in high-grade breast tumors compared to low-grade samples. Grade III tumors showed higher number of CNAs and larger aberrations than low-grade tumors and displayed a wide range of chromosomal aberrations, which were mainly 5p, 8q, 10p, 17q12, and 19 gains, and 3p, 4, 5q proximal, 9p, 11p, 18q, and 21 losses. The presence of LVI, a well-established prognostic marker, was not significantly associated with increased genomic instability in comparison to breast tumors negative for LVI, considering the total number of chromosomal alterations. However, a slightly increase in the frequency of specific alterations could be detected in LVI-positive group, such as gains at 5p, 16p, 17q12, and 19, and losses at 8p, 11q, 18q, and 21. Three newly reported small-scale rearrangements were detected in high-risk tumors (LVI-positive grade III) harboring putative breast cancer genes (amplicons at 4q13.3 and 11p11.2, and a deletion at 12p12.3). Furthermore, gene expression analysis uncovered networks highlighting S100A8, MMP1, and MED1 as promising candidate genes involved in high-grade and LVI-positive tumors. In summary, a group of genomic regions could be associated with high-risk tumors, and expression analysis pinpointed candidate genes deserving further investigation. The data has shed some light on the molecular players involved in two highly relevant prognostic factors and may further add to the understanding of the mechanisms of breast cancer aggressiveness.

The transcriptomic and proteomic effects of ectopic overexpression of miR-30d in human endometrial epithelial cells

miR-30d is known to be up-regulated during the acquisition of receptivity in the endometrium. In order to determine the transcriptomic and proteomic changes which occur after transient overexpression of miR-30d in primary endometrial epithelial cells, in vitro cultured human endometrial epithelial cells (hEECs) were studied experimentally. Two different miRNAs (scramble versus mimic; n = 15) were transiently transfected into primary hEECs from four different patients and were evaluated for mRNA and protein expression using Agilent's gene expression microarray and iTRAQ analysis techniques, respectively. A set of differentially expressed mRNAs were validated by qPCR and several differentially expressed proteins were validated by western blot. Finally, methylation differential immunoprecipitation (MeDIP) was used to validate the epigenetic changes in the H19 gene. The results showed that transient transfection with miR-30d miRNA induced the differential mRNA-expression of 176 genes (75 up-regulated and 101 down-regulated). Several of them have been associated with reproductive and endocrine system disorders, tissue development, and are implicated in epithelial cell proliferation. Also, the down-regulation of some genes such as H19 and N-methyltransferase (NNMT) may suggest that epigenetic alterations are induced. Furthermore, upstream effects of genes regulated by the estrogen receptor alpha 1 (ESR1) transcription factor have been predicted. Proteomic analysis identified 2290 proteins, of which 108 were differentially expressed (47 up-regulated and 61 down-regulated). Among these differentially expressed proteins DNA methyl transferase (DNMT)1 was found to be up-regulated; this protein participates in the maintenance of DNA methylation, supporting an epigenetic role for miR-30d. Finally MeDIP showed an increase in methylation in the H19 DMR region. In conclusion transient in vitro overexpression of the receptivity-up-regulated miRNA miR-30d in hEECs seems to activate genes which are associated with hormonal response and the epigenetic status of these cells.

HMGA2 and high-grade serous ovarian carcinoma

HMGA2, the High Mobility Group A2 gene, plays a very important role in fetal development and carcinogenesis. As an oncofetal gene, it is upregulated in tumors of both epithelial and mesenchymal tissue origin. Chromosomal translocations of HMGA2 are common in mesenchymal tumors, whereas the regulatory mechanisms of HMGA2 in malignant epithelial tumors are much more complex. As an architectural transcription factor, it is involved in multiple biological pathways by targeting different downstream genes in different cancers. HMGA2 is upregulated in both the early and late stages of high-grade serous ovarian carcinoma (HGSOC) and, according to The Cancer Genomic Atlas, is among a signature of genes overexpressed in ovarian cancer. Recent identification of miR-182 as a mediator of BRCA1 and HMGA2 deregulation in ovarian cancer cells may guide us toward a better understanding of the roles of HMGA2 in ovarian carcinogenesis. In this article, we will review recent developments and findings related to HMGA2, including its regulation, oncogenic properties, major functional pathways associated with the tumorigenesis of HGSOC, and its potential role as a biomarker for clinical application.

Fusion of HMGA2 to COG5 in uterine leiomyoma

Uterine leiomyomas are smooth muscle tumors most commonly seen in middle-aged women. Approximately 10% of these tumors contain rearrangements of the chromatin-remodeling gene HMGA2 at the chromosome band 12q14.3. Herein, we report on a uterine leiomyoma with a novel HMGA2 fusion gene. A 44-year-old woman presented with a 20-cm mass uterine leiomyoma. From a histological standpoint, the tumor exhibited extensive hyalinization, very low mitotic activity (<1/10 HPH), and no cytologic atypia. Smooth muscle differentiation was confirmed by the expression of smooth muscle actin and desmin. Standard cytogenetic analysis showed the reciprocal translocation t(7;12)(q31.2;q14.3). Fluorescence in situ hybridization analysis confirmed a balanced rearrangement of the HMGA2 locus in 80% of the cells. 3'RACE reverse-transcription polymerase chain reaction identified the fusion of HMGA2 exon 4 to the COG5 locus on 7q31 (component of oligomeric golgi complex 5 isoform). The fusion sequence is predicted to encode a 96-amino acid chimeric protein that retains all three DNA-binding domains (AT hooks) of HMGA2, but that is shorter than the original HMGA2 protein. Since the general structure of the fusion gene is similar to other previously described HMGA2 fusions, its biologic activity is predicted to be likely similar.

Identification of chromosomal aberrations of metastatic potential in colorectal carcinoma

In colorectal cancer (CRC) care, treatment decisions depend on the efforts to estimate the metastatic potential of tumors. The liver is one of the most common metastatic sites of CRC and the prognosis of CRC patients often reflects metastases to distant sites. To identify chromosomal aberrations associated with liver metastasis, we performed allelic copy number analysis for CRC with or without synchronous liver metastasis using genotyping arrays. By allelic copy number analysis of CRC samples, we observed common aberrations in 14 chromosomal arms in two groups, that is, gains on 7p22.3-p11.2, 8q22.3-q24.3, 13q12.12-q34, and 20q11.22-q13.33 and loss of heterozygosity (LOH) on 4q12-q35.1, 5q11.2-q35.3, 8p23.3-p12, 15q11.2-q26.3, 17p13.3-p11.2, 17q11.2-q25.1, 18p11.32-p11.21, 18q11.2-q23, 20p13-p12.1, and 22q11.1-q13.32. We found that gains on 20p13-p12.1 and 20q11.21-q13.33 and LOH on 6q14.1-q25.1 were more frequent in CRC with liver metastasis. We also compared chromosomal aberrations in primary CRC lesions with those of the corresponding liver metastasis and found that the allelic genome imbalance status of a metastatic lesion is similar to that of the primary cancer, which suggests that chromosomal aberrations are largely maintained on hematogenous spread. Intriguingly, several chromosomal aberrations in CRC were found in the primary cancer but not in the corresponding liver metastasis, thus suggesting heterogeneity of cancer cells within solid tumors or the presence of events uniquely developed in primary tumors. Consequently, CRC with and without liver metastasis harbor similar chromosomal aberrations, and chromosomal aberration at 6q, 20p, and 20q may be involved in the process of liver metastasis of CRC.

Overexpression of HMGA2 in uterine leiomyomas points to its general role for the pathogenesis of the disease

An overexpression of HMGA2 is supposed to be a key event in the genesis of leiomyoma with chromosomal rearrangements affecting the region 12q14-15 targeting the HMGA2 gene, but gene expression data regarding differences between uterine leiomyomas with and those without 12q14-15 aberrations are insufficient. To address the question whether HMGA2 is only upregulated in the 12q14-15 subgroup, the expression of HMGA2 was analyzed in a comprehensive set of leiomyomas (n = 180) including tumors with 12q14-15 chromosomal aberrations (n = 13) and matching myometrial tissues (n = 51) by quantitative RT-PCR. The highest expression levels for HMGA2 were observed in tumors with rearrangements affecting the region 12q14-15, but although HMGA2 is expressed at lower levels in leiomyomas without such aberrations, the comparison between the expression in myomas and matching myometrial tissues indicates a general upregulation of HMGA2 regardless of the presence or absence of such chromosomal abnormalities. The significant (P < 0.05) overexpression of HMGA2 also in the group of fibroids without chromosomal aberrations of the 12q14-15 region suggests a general role of HMGA2 in the development of the disease.

Aggressive Angiomyxoma of the Vulva With a Sole t(5;8)(p15;q22) Chromosome Change

Aggressive angiomyxoma of the vulva is uncommon and the pathogenesis remains unclear. Recently, a few cytogenetic studies demonstrated chromosomal abnormalities in aggressive angiomyxoma of the vulva. A 45-year-old Japanese woman complaining of right-side vulva tumor measuring 3 cm in diameter was referred to our hospital. The mass was located at the right side of the rectovaginal septum and was closely adherent to the rectal serosa and the levator muscle ani. The tumor was completely resected. A pathological examination demonstrated aggressive angiomyxoma of the vulva. Chromosomal analysis of the tumor demonstrated a sole t(5;8)(p15;q22) translocation. This is the first case of an aggressive angiomyxoma of the vulva with a sole t(5;8)(p15;q22) translocation.

The genetic heterogeneity of uterine leiomyomata

Research investigating the genetics of UL has already been successful in gathering epidemiologic evidence for heritability, establishing the clonal and mosaic nature of these tumors, correlating genotypic and phenotypic characteristics, defining cytogenetic subgroups, and identifying specific genes involved in tumorigenesis. Although UL are known to be benign tumors, the impact they have on the lives of so many women can only be described as "malignant". For this reason, continuing the quest to ascertain the genes, functions, and mechanisms integral to UL development is absolutely imperative. Genetic tests for personalized medical management of women with fibroids is at the threshold for providing the most appropriate treatments (Fig. 3), and combined with developing less invasive therapies portends a brighter future for a major health problem for women.

Fusion oncogenes and tumor type specificity--insights from salivary gland tumors

Salivary gland tumors are frequently characterized by recurrent chromosome translocations, which have recently been shown to result in pathogenetically relevant fusion oncogenes. These genes encode novel fusion proteins as well as ectopically expressed normal or truncated proteins, and are found in both benign and malignant salivary gland tumors. The major targets of the translocations are DNA-binding transcription factors (PLAG1 and HMGA2) involved in growth factor signaling and cell cycle regulation, and coactivators of the Notch (MAML2) and cAMP (TORC1) signaling pathways. Identification of these fusion oncogenes has contributed to our knowledge of molecular pathways leading to epithelial tumors in general, and to salivary gland tumors in particular. Interestingly, the fusions in salivary gland tumors do not seem to be as tumor type specific as those in leukemias and sarcomas. Instead, they may function by activating basic transformation pathways that can function in multiple cell types. The downstream gene products of these fusions will be important targets for development of new intracellular therapeutic strategies.

Chromosomal imbalances in some benign orbital tumours

PURPOSE

To examine benign orbital tumours for chromosomal imbalances.

METHODS

Specimens obtained from orbital tumours were screened for chromosomal imbalances using high resolution comparative genomic hybridization (CGH). The imbalances detected by CGH were confirmed by using fluorescence in situ hybridization (FISH) and loss of heterozygosity (LOH) analysis.

RESULTS

Chromosomal gains or losses were seen in 4/6 pleomorphic adenomas (gains at 8q; losses at 4p, 5p, 8p, 11p and 14q), 2/4 schwannomas (losses at 16p and 22q), and 1/9 cavernous haemangiomas (losses at 13q). Compared to previous studies of pleomorphic adenomas using G-band analysis, chromosomal imbalances were more frequently detected by using CGH. Gains of 8q11-q22 and losses of 4p15-pter, 11p12-p15, and 14q12-q23 in pleomorphic adenomas, losses of 16p12-p13 in schwannomas, and losses of 13q32-qter in cavernous haemangiomas have not been reported previously.

CONCLUSIONS

A range of chromosomal imbalances was detected even within tumours of the same histological subtype. We did not observe common chromosomal gains or losses that were characteristic for orbital presentation of the tumours. The clinical relevance of the abnormalities is uncertain, but they may indicate the position of genes that could play a role in tumour development.

Extensive expression studies revealed a complex alternative splicing pattern of the HMGA2 gene

Chromosomal rearrangements of the HMGA2 locus belong to the most common aberrations in human benign tumors. HMGA2 rearrangements often result in chimeric genes expressing transcripts consisting of the first three exons of HMGA2 followed by ectopic sequences derived from intron 3 of that gene. RT-PCR-based expression studies of 4 of these HMGA2 transcripts revealed a co-expression with the "wild-type" HMGA2a in tumor samples as well as in normal tissues. Northern blot hybridizations of the lipoma cell line Li-14 revealed the expression of five additional HMGA2 transcripts consisting of exons 1 to 3 but not exons 4 to 5 besides the full-length HMGA2a transcript. In silico analyses have been performed showing a high homology to well-established consensus sequences for the 3' splice acceptor site, the branch site, and poly(A) signal. Thus, it is quite obvious that the HMGA2 transcripts described herein are alternative, not aberrant, splice-products of the HMGA2 gene. It is hypothesized that HMGA2-dependent tumorigenesis is caused by a disturbed equilibrium in the co-expression of the HMGA2 splice variants leading to aberrant cell proliferation and/or malignant transformation of cells.

Disruption and aberrant expression of HMGA2 as a consequence of diverse chromosomal translocations in myeloid malignancies

Chromosomal translocations that target HMGA2 at chromosome band 12q14 are seen in a variety of malignancies, notably lipoma, pleomorphic salivary adenoma and uterine leiomyoma. Although some HMGA2 fusion genes have been reported, several lines of evidence suggest that the critical pathogenic event is the expression of truncated HMGA2 isoforms. We report here the involvement of HMGA2 in six patients with myeloid neoplasia, dysplastic features and translocations or an inversion involving chromosome bands 12q13-15 and either 7p12, 8q22, 11q23, 12p11, 14q31 or 20q11. Breaks within or very close to HMGA2 were found in all six cases by molecular cytogenetic analysis, leading to overexpression of this gene as assessed by RT-PCR. Truncated transcripts consisting of HMGA2 exons 1-2 or exons 1-3 spliced to intron-derived sequences were identified in two patients, but were not seen in controls. These findings suggest that abnormalities of HMGA2 play an important and previously unsuspected role in myelodysplasia.

HMGA2 is expressed in an allele-specific manner in human lipomas

The architectural transcription factor HMGA2 is almost exclusively expressed in undifferentiated mesenchymal cells. Interestingly, it has been mapped to the translocation site in a variety of human mesenchymal tumors that reveal a terminally differentiated phenotype. The expression of chimeric HMGA2 transcripts encoding three DNA-binding domains fused to novel transcriptional regulatory domains was previously described in lipomas. In this study with lipoma ST91-198, we report the expression of truncated HMGA2 transcripts that gained no functional domains. The highly polymorphic region in the 5' untranslated region (UTR) of HMGA2 was used to determine the allele-specific expression of HMGA2 in lipomas. Microsatellite PCR revealed a monoallelic expression pattern, and only the translocated allele was expressed when the DNA-binding domains of the rearranged allele were fused with transcription activation domains. Surprisingly, a diallelic expression pattern of HMGA2 was observed in lipoma ST91-198, and the wild-type allele was also expressed. In conjunction with studies involving rearrangements of HMGA genes in other benign mesenchymal tumors, our results support a model in which the expression of the wild-type HMGA allele is critical for the pathogenesis of mesenchymal tumors and in which rearrangements of HMGA do not lead to a gain of function in the chimeric HMGA protein.

Rearrangement involving chromosomes 1 and 8 in a retroperitoneal lipoma

Superficial lipomas are very common benign adipose tissue tumors. In contrast, deep-seated lipomas such as retroperitoneal lipomas, are extremely rare and have to be carefully distinguished from well-differentiated liposarcomas for appropriate treatment and follow-up. We report to, our knowledge, the first cytogenetic analysis of a retroperitoneal lipoma occurring in an adult, which showed a complex rearrangement interpreted as t(1;8)(q32;q22-q23) followed by a pericentric inversion of der(8). There was no detectable rearrangement of chromosome 12, and in particular no 12q14-q15 amplification. Because rearrangements of the 8q11-q13 region involving the PLAG1 gene have been described in lipoblastoma-another kind of benign adipose tumor--we used fluorescence in situ hybridization analysis to determine in the present case the chromosomal breakpoint on 8q was located between the ETO (8q22) and COX6C (8q22-q23) genes at a great distance from PLAG1. Karyotypic analysis of additional cases of retroperitoneal lipomas will be required to assess the significance of chromosome 1 and 8 rearrangements in a continuous effort to attain a better classification of adipose tissue tumors. Of great importance is the determination of such genetic markers as additional tools for the differential diagnosis between benign and malignant forms of adipose tumors, and to avoid erroneous diagnoses.

Translocation, deletion/amplification, and expression of HMGIC and MDM2 in a carcinoma ex pleomorphic adenoma

Carcinoma ex pleomorphic adenoma (CexPA) is a carcinoma developing within a pre-existing benign pleomorphic adenoma (PA). Here we describe the identification and characterization of a series of genetic events leading to translocation, deletion/amplification, and overexpression of the HMGIC and MDM2 genes in a CexPA at an early stage of development. The tumor had a pseudodiploid stemline karyotype with a del(5)(q22-23q32-33) and a t(10;12)(p15;q14-15). In addition, there were several sidelines with double minute chromosomes (dmin) or homogeneously staining regions (hsr). Fluorescence in situ hybridization (FISH) mapping revealed that the 12q14-15 breakpoint was located centromeric to HMGIC and that the entire gene was juxtaposed to the der(10) chromosome. Detailed analysis of cells with dmin and hsr revealed that HMGIC and MDM2 were deleted from the der(10) and that the dmin and hsr were strongly positive for both genes. Southern blot analysis confirmed that both HMGIC and MDM2 were amplified and that no gross rearrangements of the genes had occurred. Immunostaining revealed that the HMGIC protein was highly overexpressed particularly in the large polymorphic cells within the carcinomatous part of the tumor. These findings suggest that amplification and overexpression of HMGIC and possibly MDM2 might be important genetic events that may contribute to malignant transformation of benign PA.

The HMG I proteins: dynamic roles in gene activation, development, and tumorigenesis

The high mobility group I, Y, and I-C proteins are low-molecular-weight, nonhistone chromosomal proteins that play a general role modulating gene expression during development and the immune response. Consistent with their role in early development, all three proteins are expressed at high levels during embryogenesis, and their expression is markedly diminished in differentiated cells. Exceptions to the general repression of these genes in adult tissues involve (1) A burst of synthesis of the HMG I protein during the immune response (during lymphocyte activation and preceding cytokine/adhesion molecule gene expression), (2) A constitutive expression of the HMG I and Y proteins in photoreceptor cells, and (3) Derepression of HMG I, Y, and often I-C expression in neoplastic cells. Work from several laboratories has now uncovered how these proteins participate in gene activation: (1) By altering the chromatin structure around an inducible gene-and thus influencing accessibility of the locus to regulatory proteins-(2) By facilitating the loading of transcription factors onto the promoters, and (3) By bridging adjacent transcription factors on a promoter via protein/protein interactions. Despite the similar structures and biochemical properties of the three proteins, the work has also provided clues to a division of labor between these proteins. HMG I and Y have demonstrable roles in enhanceosome formation, whereas HMG I-C has a specific role in adipogenesis. C-terminal truncations of HMG I-C and wild-type HMG Y appear to function in a manner analogous to oncogenes, as assessed by cellular transforation assays and transgenic mice. Future work should clearly define the similarities and differences in the biological roles of the three proteins, and should evolve to include attempts at pharmaceutical intervention in disease, based upon structural information concerning HMG I interactions with DNA and with regulatory proteins.

Evidence for RAD51L1/HMGIC fusion in the pathogenesis of uterine leiomyoma

Chromosome rearrangements involving 12q15 are frequently observed in a variety of human mesenchymal tumors. The high mobility group protein gene HMGIC has been identified as the target involved in these rearrangements. Uterine leiomyomas frequently use chromosome band 14q24 as a translocation partner to HMGIC. Recent studies within the chromosome 14 breakpoint region in cell lines carrying t(12;14)(q15;q23-24) revealed that RAD51L1, a member of the RAD51 recombination gene family, is the HMGIC partner. Using RT-PCR, we screened a panel of 81 uterine leiomyomas removed from 30 women for rearrangement between RAD51L1 and HMGIC. This is the first molecular analysis in which primary tumors have been examined for the RAD51L1/HMGIC transcripts. The chimeric transcripts were identified from two cases in which exon 7 of the RAD51L1 gene is fused in frame to either exon 2 or exon 3 of the HMGIC gene. These transcripts encode fusion proteins containing RAD51L1 nucleotide binding domains and the HMGIC protein lacking the N-terminal AT hook motifs. The detection of the RAD51L1/HMGIC fusion in primary tumors adds to the accumulating evidence implicating this fusion in a proportion of uterine leiomyoma patients.

Fusion of a sequence from HEI10 (14q11) to the HMGIC gene at 12q15 in a uterine leiomyoma

Uterine leiomyoma, a benign smooth-muscle tumor of the myometrium, is the most commonly encountered neoplasm in women of reproductive age. Band q15 of chromosome 12 is often rearranged in benign mesenchymal tumors such as uterine leiomyomas, and the HMGIC gene, encoding a protein of the high-mobility-group (HMG), is present in that region. Using 3' rapid amplification of cDNA ends (3'RACE) experiments, we isolated an ectopic sequence that was fused to HMGIC in a uterine leiomyoma. Cloning of the fusion cDNA identified a gene termed rising dbl quote, left (low)homo sapiens enhancer of invasion 10" (HEI10) as the fusion partner. Radiation hybrid mapping revealed that the normal location of HEI10 is at 14q11. In the fusion transcript the first two exons of the HMGIC gene, which encode DNA-binding domains, were fused to the 3' portion of the HEI10 gene. This rearrangement implicates HMGIC in the tumorigenesis of uterine leiomyoma, and suggests that its fusion HMGIC product may play a role in mesenchymal differentiation.