Rearrangement of the neoplasia-associated geneHMGIC in synovia from patients with osteoarthritis

Constitutional rearrangement of the architectural factor HMGA2: a novel human phenotype including overgrowth and lipomas

Although somatic mutations in a number of genes have been associated with development of human tumors, such as lipomas, relatively few examples exist of germline mutations in these genes. Here we describe an 8-year-old boy who has a de novo pericentric inversion of chromosome 12, with breakpoints at p11.22 and q14.3, and a phenotype including extreme somatic overgrowth, advanced endochondral bone and dental ages, a cerebellar tumor, and multiple lipomas. His chromosomal inversion was found to truncate HMGA2, a gene that encodes an architectural factor involved in the etiology of many benign mesenchymal tumors and that maps to the 12q14.3 breakpoint. Similar truncations of murine Hmga2 in transgenic mice result in somatic overgrowth and, in particular, increased abundance of fat and lipomas, features strikingly similar to those observed in the child. This represents the first report of a constitutional rearrangement affecting HMGA2 and demonstrates the role of this gene in human growth and development. Systematic genetic analysis and clinical studies of this child may offer unique insights into the role of HMGA2 in adipogenesis, osteogenesis, and general growth control.

Chromosomal abnormalities in inflammatory pseudotumor of the urinary bladder

Inflammatory pseudotumors of the urinary bladder are rare, benign, nonepithelial tumors. Fewer than 30 have been reported, and no data are available on their karyotypic characteristics and/or the molecular mechanisms of pathogenesis. We performed short-term culturing and cytogenetic analysis of an inflammatory pseudotumor of the bladder, finding a der(20)t(12;20)(q13 approximately q15;q13) as the only cytogenetic aberration. The detection of a 12q13 approximately q15 rearrangement in the inflammatory pseudotumor indicates that this lesion is pathogenetically related to other benign mesenchymal tumors displaying, for example, lipogenic or leiomyomatous differentiation, something that is in sharp contrast to the karyotypic profile of epithelial tumors of the urinary bladder mucosa.

HMGIC alterations in smooth muscle tumors of soft tissues and other sites

The HMGIC gene, which codes a protein that acts as an architectural transcription factor, is frequently rearranged in a variety of benign or locally aggressive mesenchymal tumors. In tumors of smooth muscle differentiation, only uterine leiomyoma and lipoleiomyoma are known to be associated with the altered HMGIC. We investigated molecular and genetic alterations of the HMGIC in 36 benign and malignant smooth muscle tumors arising at various anatomical sites, including 13 uterine leiomyomas, two leiomyomas of the kidney with a t(12;14), one pelvic lipoleiomyoma, one vascular leiomyoma of the foot, two uterine leiomyosarcomas, six retroperitoneal leiomyosarcomas, one leiomyosarcoma of the urinary bladder, and 10 leiomyosarcomas of external soft tissues. HMGIC gene expressions were detected in both uterine (73.3%) and extrauterine (57.1%) smooth muscle tumors by reverse transcriptase polymerase chain reaction (RT-PCR), and benign tumors (70.5%) more frequently expressed the HMGIC than leiomyo-sarcomas (57.8%). Variant transcripts of the HMGIC containing cryptic exonic sequences previously described were found in one renal and three uterine leiomyomas and four leiomyosarcomas arising in the uterus and soft tissues by RT-PCR. Southern blot analysis identified a rearranged HMGIC in one soft tissue leiomyosarcoma. Thus, the HMGIC alterations in smooth muscle tumors are not confined only to uterine leiomyoma or lipoleiomyoma. Our data expand the variety of mesenchymal tumors associated with HMGIC alterations.

Cumulative dosage effect of a RAD51L1/HMGA2 fusion and RAD51L1 loss in a case of pseudo-Meigs' syndrome

Uterine leiomyoma presenting with ascites and pleural fluid is referred to as pseudo-Meigs' syndrome. It is unclear whether common uterine leiomyomas and uterine leiomyomas causing pseudo-Meigs' syndrome are cytogenetically related or whether functionally different primary pathogenetic triggers are responsible for the differences in tumor phenotype. In this study, we investigated the possible involvement of RAD51LI and HMGA2 (formerly known as HMGIC) in initiation and/or progression of a huge uterine leiomyoma presenting as pseudo-Meigs' syndrome. The detailed cytogenetic and FISH analysis revealed the presence of two subclones with a complex karyotype, 46,XX,t(2;12)(q31;q21),ins(14;12)(q23-24;q15q21).ish del(12)(q15q15) (LL12NC01-142H1-,LL12NC01-27E12-),der(12)t(2;12)(LL12NC01-142H1+,LL12NC01-27E12-),der(14)ins(14;12)(q22;q15q15) (LL12NC01-142H1+,LL12NC01-27E12+,RAD51LI+), der(14)ins(14;12)(q23-q24;q15q21) (LL12NC01-142H1-, LL12NC01-27E12+) [20]/46,idem,del(14)(q21q24).ish(RAD51LI-) [6], indicating intragenic HMGA2 rearrangement and loss of one of the RAD51LI alleles in a derivative subclone with chromosome 14 deletion. Furthermore, RACE and RT-PCR analysis of the tumor cells did not reveal abnormal HMGA2 or RAD51LI transcripts. Additionally, the cellular subclone with intrachromosomal 14q21-q24/RAD51LI deletion showed an in vitro growth advantage over the subclone without the deletion. This observation supports a model in which accumulation of two independent mutations-a classical structural rearrangement involving HMGA2 and RAD51L1, in combination with a loss of the second RAD51L1 allele-might play a major role in the development of pseudo-Meigs' syndrome.

The tumor-associated gene HMGIC is expressed in normal and osteoarthritis-affected synovia

Chromosomal rearrangements involving chromosome bands 12q13-15 are very frequent findings in benign solid tumors, and recently, the primary molecular target for these aberrations was identified as the gene HMGIC. However, mutations in this gene have also been observed in nonneoplastic tissues. In a previous study, we reported breakpoints within HMGIC of synovia affected by osteoarthritis (OA) in two cases with 12q15 aberrations. To analyze further the role of HMGIC in this disease, we have performed cytogenetic, fluorescent in situ hybridization (FISH), RNA, and protein expression analyses on synovial samples from patients with OA and individuals without signs of the disorder. Cytogenetic analysis of short-term cultured cells revealed clonal 12q13-15 aberrations in 2/36 cases of OA synovia and no rearrangement in any of the five controls. With FISH analysis, it was shown that the chromosomal breakpoints in the two aberrant cases were located outside the HMGIC locus. In contrast, at RNA and protein expression analyses, OA-affected as well as normal synovia displayed transcription and translation of the gene. We also analyzed whether immunoreactivity for HMGIC was associated with the proliferation-specific antigen Ki-67, but no correlation between the staining patterns of these proteins was observed. From the results of the present study, it is evident that expression of HMGIC cannot simply be considered a sign of neoplasia or an effect of proliferation.

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.