Molecular cytogenetic characterization of del(7q) in two uterine leiomyoma-derived cell lines

Cytogenomic Profile of Uterine Leiomyoma: In Vivo vs. In Vitro Comparison

We performed a comparative cytogenomic analysis of cultured and uncultured uterine leiomyoma (UL) samples. The experimental approach included karyotyping, aCGH, verification of the detected chromosomal abnormalities by metaphase and interphase FISH, MED12 mutation analysis and telomere measurement by Q-FISH. An abnormal karyotype was detected in 12 out of 32 cultured UL samples. In five karyotypically abnormal ULs, MED12 mutations were found. The chromosomal abnormalities in ULs were present mostly by complex rearrangements, including chromothripsis. In both karyotypically normal and abnormal ULs, telomeres were ~40% shorter than in the corresponding myometrium, being possibly prerequisite to chromosomal rearrangements. The uncultured samples of six karyotypically abnormal ULs were checked for the detected chromosomal abnormalities through interphase FISH with individually designed DNA probe sets. All chromosomal abnormalities detected in cultured ULs were found in corresponding uncultured samples. In all tumors, clonal spectra were present by the karyotypically abnormal cell clone/clones which coexisted with karyotypically normal ones, suggesting that chromosomal abnormalities acted as drivers, rather than triggers, of the neoplastic process. In vitro propagation did not cause any changes in the spectrum of the cell clones, but altered their ratio compared to uncultured sample. The alterations were unique for every UL. Compared to its uncultured counterpart, the frequency of chromosomally abnormal cells in the cultured sample was higher in some ULs and lower in others. To summarize, ULs are characterized by both inter- and intratumor genetic heterogeneity. Regardless of its MED12 status, a tumor may be comprised of clones with and without chromosomal abnormalities. In contrast to the clonal spectrum, which is unique and constant for each UL, the clonal frequency demonstrates up or down shifts under in vitro conditions, most probably determined by the unequal ability of cells with different genetic aberrations to exist outside the body.

Identification of CUX1 as the recurrent chromosomal band 7q22 target gene in human uterine leiomyoma

Uterine leiomyomas are benign solid tumors of mesenchymal origin which occur with an estimated incidence of up to 77% of all women of reproductive age. The majority of these tumors remains symptomless, but in about a quarter of cases they cause leiomyoma-associated symptoms including chronic pelvic pain, menorrhagia-induced anemia, and impaired fertility. As a consequence, they are the most common indication for pre-menopausal hysterectomy in the USA and Japan and annually translate into a multibillion dollar healthcare problem. Approximately 40% of these neoplasms present with recurring structural cytogenetic anomalies, including del(7)(q22), t(12;14)(q15;q24), t(1;2)(p36;p24), and anomalies affecting 6p21 and/or 10q22. Using positional cloning strategies, we and others previously identified HMGA1, HMGA2, RAD51L1, MORF, and, more recently, NCOA1 as primary target (fusion) genes associated with tumor initiation in four of these distinct cytogenetic subgroups. Despite the fact that the del(7)(q22) subgroup is the largest among leiomyomas, and was first described more than twenty years ago, the 7q22 leiomyoma target gene still awaits unequivocal identification. We here describe a positional cloning effort from two independent uterine leiomyomas, containing respectively a pericentric and a paracentric chromosomal inversion, both affecting band 7q22. We found that both chromosomal inversions target the cut-like homeobox 1 (CUX1) gene on chromosomal band 7q22.1 in a way which is functionally equivalent to the more frequently observed del(7q) cases, and which is compatible with a mono-allelic knock-out scenario, similar as was previously described for the cytogenetic subgroup showing chromosome 14q involvement.

Definition of a minimal region of deletion of chromosome 7 in uterine leiomyomas by tiling-path microarray CGH and mutation analysis of known genes in this region

Somatic interstitial deletions of chromosome segment 7q22-q31 in uterine leiomyomas are a frequent event, thought to be indicative of a tumor suppressor gene in the region. Previous LOH and CGH studies have refined this region to 7q22.3-q31, although the target gene has not been identified. Here, we have used tiling-path resolution microarray CGH to further refine the region and to identify homozygous deletions in fibroids. Furthermore, we have screened all manually annotated genes in the region for mutations. We have refined the minimum deleted region at 7q22.3-q31 to 2.79 Mbp and identified a second region of deletion at 7q34. However, we identified no pathogenic coding variation.

Microallelotyping defines novel regions of loss of heterozygosity in uterine leiomyomas

Uterine leiomyomas are extremely common, benign, smooth muscle tumors that represent a significant public health problem. Although there have been few molecular studies of uterine leiomyomas, most of them have reported a very low frequency of loss of heterozygosity (LOH) in different regions of the genome. The detection of LOH has been used to identify genomic regions that harbor tumor suppressor genes and to characterize different tumor types. We have used a set of 15 microsatellite polymorphism markers to examine the frequency of allele loss in a panel of 64 human uterine leiomyomas matched to normal DNAs. The markers were chosen from regions involved in losses identified by comparative genomic hybridization in a subset of uterine leiomyomas described in a previous report. DNA from tumors and normal tissue was amplified by the polymerase chain reaction and subsequently analyzed using an ABI Prism 377 DNA automated sequencer. The frequency of LOH observed was low, except for the markers D15S87 (15q26.3), D7S493 (7p15.3), and D7S517 (7p22.2). No changes in microsatellite size were detected in our samples. These results provide useful clues for identifying putative tumor suppressor genes associated with a subset of uterine leiomyomas. (c) 2004 Wiley-Liss, Inc.

Telomerase immortalization of human myometrial cells

Several strategies have been described for the primary culture of human myometrial cells. However, primary cultures of myometrial cells have a limited life span, making continual tissue acquisition and cell isolation necessary. Recent studies have demonstrated that cell culture life span is related to chromosomal telomere length, and cellular senescence results from progressive telomere shortening and the lack of telomerase expression. Transfection of cells with expression vectors containing the human telomerase reverse transcriptase (hTERT) maintains telomere length and effectively gives normal cells an unlimited life span in culture. In addition, hTERT extends the life span of cultured cells far beyond normal senescence without causing neoplastic transformation. In the present study, we developed a cell line from hTERT-infected myometrial cells (hTERT-HM). Cells were isolated from myometrial tissue obtained from women undergoing hysterectomy, and retroviral infection was used to express the catalytic subunit of telomerase in myometrial cells. Cells expressing hTERT have been in continuous culture for >10 mo, whereas the control culture senesced after approximately 2 mo. Telomerase activity was monitored in cells with a polymerase chain reaction-based telomerase activity assay. Telomerase-expressing cells contained mRNA for alpha smooth muscle actin, smoothelin, oxytocin receptor, and estrogen receptor alpha, but the estrogen receptor beta receptor was lost. Immunoblotting analysis identified the expression of calponin, caldesmon, alpha smooth muscle actin, and oxytocin receptor. Although estrogen receptor expression was below the level of detection with immunoblotting, transfection experiments performed with reporter constructs driven by estrogen response elements demonstrated estrogen responsiveness in the hTERT-HM. In addition, treatment of hTERT-HM with oxytocin caused a concentration-dependent increase in intracellular calcium levels, confirming the presence of functional oxytocin receptors. Myometrial cells immortalized with hTERT retained markers of differentiation that are observed in primary cultures of smooth muscle cells. The expression of various smooth muscle/myometrium cell markers suggests that these cells may be an appropriate model system to study certain aspects of human myometrial function.

Lessons from pregnancy and parturition: uterine leiomyomas result from discordant differentiation and dedifferentiation responses in smooth muscle cells

Leiomyomas, benign smooth muscle tumors of the uterus, are the most common gynecological neoplasm in women. Studies with human tissues and primary cultures have revealed little about the development of leiomyomas, although several genes have been shown to be differentially expressed in leiomyomas compared to matched normal myometrium. We propose that uterine smooth muscle tumor cells mimic a differentiated myometrial cell of pregnancy, and are associated with a hypersensitivity to sex steroid hormones, preventing the cells from responding to normal apoptotic or dedifferentiation signals which would return the cells to a nongravid phenotype. Support of this hypothesis is derived from experimental studies in female Eker rats which develop uterine leiomyoma with many similarities to the human disease. Members of the steroid receptor superfamily as well as the binding partners and co-regulators necessary for transactivation and gene transcription, may be involved in the altered pathway of cellular differentiation and regulation observed in uterine leiomyomas.

Allelotype of uterine leiomyomas

Uterine leiomyomas are the most common benign tumor that arise from smooth muscle cells of the myometrium. Little is known about the etiology and pathogenesis of this tumor. To investigate the molecular pathogenesis of these tumors, we have conducted an allelotype of 102 leiomyomas from 12 patients, using 67 fluorescently-tagged oligonucleotide primers amplifying microsatellite loci covering all autosomes. No areas of the genome showed frequent loss of heterozygosity (LOH); however, the highest rate of LOH (9%) was observed on 7q, consistent with previous cytogenetic observations. Uterine leiomyomas are sometimes multiple. In general, multiplicity of other types of neoplasm is associated with genetic predisposition to the disease. Because multiple tumors were available from each of the 12 patients studied, we looked for evidence of allele-specific LOH, which might indicate the presence of an underlying predisposition gene. However, no evidence for allele-specific LOH was detected, indicating that if cases of multiple uterine leiomyoma are due to an underlying predisposition gene, it is unlikely to be a recessive oncogene.

Expression of HMGIY in three uterine leiomyomata with complex rearrangements of chromosome 6

Uterine leiomyomata (UL) are a major public health problem, yet little is known about their etiology. Genetic factors likely influence UL development and growth; for example, approximately 40% of UL have chromosomal abnormalities detectable by conventional cytogenetic analysis, including t(12;14)(q15;q23-24), rearrangements involving the short arm of chromosome 6 and interstitial deletions of the long arm of chromosome 7. Two high-mobility group (HMG) protein genes, HMGIC and HMGIY, located at 12q15 and 6p21.3, respectively, are involved in rearrangements in various mesenchymal tumors including UL. In this study, we investigated HMGIY expression in three UL with complex cytogenetic rearrangements of 6p21.3 by reverse transcriptase-polymerase chain reaction (RT-PCR) and electrophoretic shift assay (EMSA). Our findings suggest that there are multiple mechanisms for HMGIY dysregulation, which may include post-translational modification of the hmgiy protein and dysregulation due to different translocation partners. Furthermore, the mechanism dysregulating HMGIY in UL with 6p21.3 and 14q23-24 rearrangements may be similar to the mechanism dysregulating HMGIC in UL characterized as t(12;14)(q15;q23-24), because of the common involvement of an HMG gene and a gene at 14q23-24.

Deletion 7q in uterine leiomyoma: fluorescence in situ hybridization characterization on primary cytogenetic preparations

Deletions of the long arm of chromosome 7 constitute one of the most common clonal chromosomal changes associated with uterine leiomyoma cells. Recently, the molecular cytogenetic refinement of 7q deletions in two myoma-derived cell lines, with the use of a panel of 39 ordered 7q DNA probes corresponding to 87 genetic markers, showed results in line with those obtained by loss of heterozygosity (LOH) analysis. Referring to this panel, we extended fluorescence in situ hybridization (FISH) analysis on primary cytogenetic preparations from three myomas with del(7q), thereby avoiding cell passages. This was fundamental in the maintenance of cells with del(7q) in the two cases showing mosaicism (i.e., the presence of an extra normal clone), which are prone to lose the abnormal clone in the very early passages. The data obtained, together with previously published findings on the two leiomyoma-derived cell lines, indicated a commonly deleted region of 11 cM. If the fact that the presence of normal cells may interfere with LOH analysis is taken into account, the FISH approach seems to be a reliable complementing tool for refining the deletion and analyzing the smallest overlapping region in cases with both normal and del(7q) cells.

ORC5L, a new member of the human origin recognition complex, is deleted in uterine leiomyomas and malignant myeloid diseases

A new member of the human origin recognition complex (ORC) was cloned and identified as ORC5L. HsORC5p is a 50-kDa protein whose sequence is 38% identical and 62% similar to ORC5p from Drosophila melanogaster. Two alleles of ORC5L were identified, one with and one without an evolutionarily conserved purine nucleotide binding motif. HsORC5p is precipitated from cell extracts with HsORC2p and HsORC4p, indicating that it is part of the putative human ORC. The bulk of HsORC5p is in an insoluble nuclear fraction, whereas the other known human ORC subunits (HsORC1p, HsORC2p, and HsORC4p) are easily extracted in the nuclear-soluble fractions and in S100 (HsORC1p). In addition, we identified an alternatively spliced mRNA from the same locus (HsORC5T). HsORC5Tp also formed a complex with HsORC4p but not with HsORC2p, suggesting it may play a regulatory role in the assembly of different ORC subcomplexes. HsORC5, HsORC5T, and HsORC4 transcripts are abundant in spleen, ovary, and prostate in addition to tissues with high levels of DNA replication like testes and colon mucosa, implicating the human ORC proteins in functions besides DNA replication. Finally, the gene for ORC5L is located at chromosome 7, band q22, in the minimal region deleted in 10% of uterine leiomyomas and in 10-20% of acute myeloid leukemias and myelodysplastic syndromes.

Molecular anatomy of chromosome 7q deletions in myeloid neoplasms: evidence for multiple critical loci

Complete or partial deletions of the long arm of chromosome 7 (7q- and -7) are nonrandom abnormalities seen in primary and therapy-induced myelodysplasia (MDS) and acute myelogenous leukemia (AML). Monosomy 7, occurring as the sole cytogenetic anomaly in a small but significant number of cases, may denote a dominant mechanism involving critical tumor suppressor gene(s). We have determined the extent of allele loss in cytogenetically prescreened MDS and AML patients for microsatellite markers from chromosome 7q22 and 7q31. Whereas >80% of these cases revealed allele loss for the entire region, a rare case of the 7q- chromosome showed allele loss for only the proximal 7q31.1 loci flanked by the markers D7S486 and D7S2456, and a case of monosomy 7 revealed allele loss for loci at both 7q31 and 7q22 with retention of sequences between these sets of loci. Furthermore, a case of AML with no cytogenetic anomaly of chromosome 7 revealed a submicroscopic allelic imbalance for a third distal locus, D7S677. These findings suggest the presence of three distinct critical loci that may contribute alone or in combination to the evolution of MDS and AML. The data also provide molecular evidence for unbalanced translocation with noncontiguous deletions, as an alternate mechanism underlying monosomy 7.

HMGIC expressed in a uterine leiomyoma with a deletion of the long arm of chromosome 7 along with a 12q14-15 rearrangement but not in tumors showing del(7) as the sole cytogenetic abnormality

Cytogenetic studies on uterine leiomyomas have shown that more than 60% of these tumors possess a normal karyotype and that 30% have clonal chromosomal aberrations. The most frequent changes are aberrations involving 12q14-15 and show rearrangements of the long arm of chromosome 7. Recently, we were able to demonstrate that in a variety of mesenchymal tumors showing 12q14-15 aberrations the HMGIC gene is rearranged thus playing a role in tumorigenesis. Here we report the results of HMGIC expression studies by RT-PCR of five uterine leiomyomas with different karyotypes. The RT-PCR studies were performed on two primary tumors showing a 12q14-15 aberration, one of which with an additional del(7) and three tumors with del(7) as the sole aberration. The tumor with the 12q14-15 aberration as the sole alteration and the leiomyoma with 12q14-15 rearrangement plus deletion of the long arm of chromosome 7 were shown to express HMGIC. In contrast, in all three tumors with the del(7) as the sole aberration no expression of HMGIC was noted.