Recent findings on genetic changes in uterine leiomyomas suggest these benign tumors being a heterogeneous group of diseases in terms of molecular pathogenesis with those showing karyotype ...alterations as well as those characterized only by cytogenetically invisible mutations of mediator subcomplex 12 (MED12). Herein, five uterine leiomyomas (UL) with an apparently normal karyotype that lacked MED12-mutations were investigated by copy number variation arrays along with their matching myometrium to search for small genomic imbalances.
Of five tumors one showed chromothripsis-like phenomena with numerous gains and losses of small segments mainly clustered to five chromosomal regions i.e. 2p14-2pter, 2q33.1-2q37.3, 5q31.3-5qter,11q14.1-11qter, and 18p11.21-18q2.3. Apparently, these cells had escaped detection by classical cytogenetics. Histologically, the tumor presented as a cellular leiomyoma with extended hyalinization. Of the remaining four tumors, one had a small intragenic deletion of the HMGA2 gene that was lacking in the corresponding myometrium. The other three tumors did not show relevant copy number alterations at all.
Overall, the results suggest that leiomyomas with an apparently normal karyotype based on classical cytogenetics and lacking MED12 mutations represent a heterogeneous group of diseases. While the HMGA2 deletion detected in one of the tumors likely represents the driver mutation and, due to its size, has escaped detection by classical cytogenetics, the extended genomic imbalances detected in one of the other cases cannot be overlooked by this method suggesting an inability of the affected cells to divide in vitro. Of particular interest in that case is the occurrence of so-called "chromothripsis" or "firestorms" without involvement of the loci of common chromosomal rearrangements in UL, as e.g. 12q14 ~ 15 and 6p21. While chromothripsis was initially described as a hallmark of malignancy, the etiology and significance of this phenomenon in benign tumors still remain obscure. In uterine smooth muscle tumors, these changes per se do not indicate malignancy.
Mutations of mediator subcomplex 12 (MED12) and of high mobility group protein AT-hook 2 (HMGA2) are driver mutations in uterine leiomyomas (UL) that have not been observed to coexist in one tumor ...and even rarely coexist in different UL tumors of one patient. Here we describe a patient who underwent hysterectomy because of multiple leiomyomas which were studied by cytogenetics, MED12 hotspot sequencing, and copy number variation arrays. Two of the UL tumors had different HMGA2 rearrangements not detected by G-banding. Two UL tumors had deletions of the long arm of chromosome 3, in one case associated with a MED12 mutation. Both deletions lead to the loss of MED12L showing strong similarity with MED12. It remains to be determined if this gene can play a role in leiomyomagenesis independent of MED12. In summary, the patient presented exhibits an unusual coincidence of different driver mutations among her leiomyomas.
Epitheloid leiomyoma is a rare subtype of benign smooth muscle tumors.
Herein, we present the results of classical cytogenetics, MED12 mutation analysis, and copy number variation array evaluation in ...one such case. Whereas cytogenetic did not show evidence for clonal chromosome abnormalities and no MED12 mutation in the "fibroid hot spot" region was detected, array hybridization revealed multiple abnormalities. Most noteworthy, almost all chromosomes showed copy-number neutral loss of heterozygosity. As examples of further abnormalities, trisomies of chromosomes 8, 12, 20, and X were noted.
The data presented suggest a near-haploid karyotype of the tumor as the initial genetic alteration followed by secondary duplications of large parts of the genome. The absence of any clonal karyotypic alterations after performing classical cytogenetics is likely explained by a reduced ability of the tumor cells to proliferate in vitro. However, to the best of our knowledge this is the first report of an uterine leiomyoma showing extended uniparental disomy. It remains to be determined if this is a more common phenomenon in epithelioid leiomyomas or even subsets of "ordinary" leiomyomas.
► HMGA2 is a protein implicated in proliferation and differentiation of mesenchymal stem cells. ► BMP4 stimulates the expression of HMGA2 in adipose tissue derived stem cells. ► In contrast BMP4 does ...not lead to a HMGA2 response in bone marrow derived stem cells.
BMP4 has been linked to early steps of adipocyte lineage differentiation but only little is known about its corresponding downstream pathways. Herein, we have investigated whether or not the expression of high mobility group protein HMGA2, another protein linked to proliferation and differentiation within the process of adipogenesis, may be influenced by BMP4 signaling in adipose tissue derived stem cells. Compared to FGF1, a strong inducer of HMGA2 in immortalized pre-adipocytes, BMP4 was found moderately to induce the HMGA2 mRNA expression in serum starved adipose tissue derived stem cells and myometrial cells. In contrast, no such activity was noted in canine bone marrow derived mesenchymal stem cells. As to adipocyte lineage differentiation the functions of BMP4 and HMGA2 mechanistically overlap. Thus, we propose that in adipose tissue BMP4 acts in part by activating HMGA2 making this architectural transcription factor one of the major downstream players in that system.
In human fibroids genes encoding the high-mobility proteins containing the 'AT-hook' DNA-binding motif (HMGA) are frequently affected by non-random chromosomal rearrangements. Thus, the different ...proteins and their derivatives resulting from these genomic rearrangements can be assumed to be involved in the genesis of these tumors by activation of largely identical downstream pathways. Constructs encoding HMGA proteins and their relevant derivatives were overexpressed in human myometrial cells, and RNA isolated from these cells was hybridized to filter arrays. Four genes were either up- or down-regulated at least 2-fold after overexpression of either of the HMGA genes and their derivatives. FGF2 (fibroblast growth factor 2) was one of these genes, and we were then able to show by microarray analyses that tumors with rearrangements of the HMGA2 locus (n = 8) expressed significantly higher levels of FGF2 than those with an apparently normal karyotype (n = 47). Accordingly, by quantitative real-time PCR uterine leiomyomas with rearrangements of the HMGA2 locus were found to express significantly higher levels of FGF2 than those with an apparently normal karyotype with a linear relationship between the expression of FGF2 and the level of HMGA2 overexpression as well as the tumor size. The results of western blot analyses confirmed these findings. Moreover, stimulation of myometrial tissue by FGF1, a strong inducer of HMGA2, leads to an increase of HMGA2 as well as FGF2 expression. In conclusion, the results contribute to the understanding of the association between the overexpression of HMGA proteins, the regulation of FGF2 expression and the size of fibroids.
Deletions of the gene encoding mediator subcomplex 12 (MED12) in human smooth muscle tumors rank among the most frequent genomic alterations in human tumors at all. In a minority of these cases, ...small deletions are found. In an attempt to delineate key features of the deletions aimed at a better understanding of the molecular pathogenesis of uterine smooth muscle tumors we have analyzed 70 MED12 deletions including 46 cases from the literature and 24 own unpublished cases.
The average length of the deletions was 18.7 bp ranging between 2 bp and 43 bp. While in general multitudes of 3 clearly dominated leaving the transcript in frame, deletions of 21, 24, 30, and 33 nucleotides were clearly underrepresented. Within the DNA segment affected deletion breakpoints were not randomly distributed. Most breakpoints clustered within the center of the segment where two peaks of breakpoint clusters could be distinguished. Interestingly, one of these clusters coincides with the loop of a putative folded non-B DNA structure whereas a much lower number of breaks noted in the 5' and 3' stem of the structure forming an intramolecular B-helix. The second cluster mainly consisting of 3' breaks was located in a region downstream adjacent to the stem.
The present study describes for the first time main characteristics of MED12 deletions occurring in smooth muscle tumors. Interestingly, the non-random distribution of breakpoints within the deletion hotspot region may point to a role of non-canonical DNA structures for the occurrence of these mutations and the molecular pathogenesis of uterine smooth muscle tumors, respectively.
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