Sylke Wanschura

Recurrent rearrangements in the high mobility group protein gene, HMGI-C, in benign mesenchymal tumours

We recently showed that the 1.7 megabase multiple aberration region (MAR) on human chromosome 12q15 harbours recurrent breakpoints frequently found in a variety of benign solid tumours. We now report a candidate gene within MAR suspected to be of pathogenetical relevance. Using positional cloning, we have identified the high mobility group protein gene HMGI–C within a 175 kilobase segment of MAR and characterized its genomic organization. By FISH analysis, we show the majority of the breakpoints of eight different benign solid tumour types fall within this gene. By Southern blot and 3′–RACE analysis, we demonstrate consistent rearrangements in HMGI–C and/or expression of altered HMGI–C transcripts. These results suggest a link between a member of the HMG gene family and benign solid tumour development.

HMGIY is the target of 6p21.3 rearrangements in various benign mesenchymal tumors

Specific chromosomal abnormalities of chromosomal region 6p21.3 have been described in subsets of many benign mesenchymal tumors. In the presented study, we investigated a series of 36 such cases by FISH, and Southern blot analyses for HMGIY rearrangements. FISH results revealed that the chromosomal breakpoints of 11 pulmonary chondroid hamartomas (PCHs), 12 endometrial polyps (EPs), one lipoma, and two uterine leiomyomas (ULs) were located within a 80 kb region surrounding the HMGIY gene. In 11 PCHs and one UL the breakpoints were located 3′ of HMGIY, and one PCH showed a breakpoint 5′ of HMGIY. Southern blot analyses with intra‐ and extragenic probes were performed of primary tumor material or cell lines from one UL, three PCHs, and five EPs. In none of these cases was an intragenic rearrangement found. Finally, we were able to detect expression of truncated HMGIY transcripts by 3′‐RACE PCR. Our data clearly show the role of a further member of the HMGI family in the development of benign mesenchymal tumors. Although most of the breakpoints of the chromosomal translocations involving HMGIY are located outside the gene, aberrant transcripts resembling the structure of those observed in the case of HMGIC have been found. Our molecular investigations thus led to the identification of the molecular mechanism by which rearrangements of either of two closely related genes lead to the development of frequent benign mesenchymal tumors in humans. Genes Chromosomes Cancer 23:279–285, 1998.

A fibroadenoma with a t(4;12) (q27;q15) affecting the HMGI-C gene, a member of the high mobility group protein gene family

SummaryAn intracanalicular fibroadenoma of the breast showing a clonal chromosomal aberration t(4;12) (q27;q15) as the sole cytogenetic abnormality is described. In order to narrow down the breakpoint region on chromosome 12 on the molecular level we performed fluorescencein situ hybridization (FISH) analysis with a cosmid pool originating from a YAC-contig overspanning part of the region 12q14–15. We were able to narrow down the breakpoint to an approximately 230kb fragment belonging to the HMGI-C gene which maps within an area recently designated as MAR (Multiple Aberration Region). The chromosomal breakpoints of other frequent benign solid tumors, i.e. lipomas, uterine leiomyomas, and pleomorphic adenomas are clustered within the third intron of that gene.

An endometrial polyp with a rearrangement of HMGI-C underlying a complex cytogenetic rearrangement involving chromosomes 2 and 12

Cytogenetic studies of an endometrial polyp of an 82-year-old patient revealed a karyotype 46,XX,der(2)inv(2)(p25q21)ins(2;12)(p25;q13q14)t(2;12)(q21; q15),der(12)del(12)(q13q14)del(12)(q15). By fluorescence in situ hybridization (FISH) we found the chromosome 12 translocation breakpoint to be mapping within the third intron of the HMGI-C gene also harboring the breakpoints of translocations involving 12q15 seen in uterine leiomyomas, lipomas, pleomorphic adenomas, and pulmonary chondroid hamartomas.

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.

Amplification and expression of the HMGIC gene in a benign endometrial polyp

In a totally benign endometrial polyp, double minute chromosomes were shown to contain an amplified and apparently nonrearranged HMGIC gene, expressed in the tumor cells, suggesting amplification of HMGIC through double minute chromosome formation as another hitherto unreported mechanism associated with the development of some mesenchymal tumors. Genes Chromosomes Cancer 22:95–99, 1998.

Malignant progression of an HPV16-immortalized human keratinocyte cell line (HPKIA) in vitro

The DNA of human papillomavirus (HPV) types found in cervical carcinomas can immortalize primary human keratinocytes. However, in analogy to tumor progression in vivo, HPV-immortalized keratinocytes require secondary events for malignant conversion. Here, we report on an HPV16-immortalized keratinocyte cell line (HPKIA) which after gamma-irradiation and long term culturing in vitro has acquired the ability to form squamous cell carcinomas in nude mice. The HPV16 integration locus and the viral transcript pattern of HPKIA cells at different passages have remained unaltered. A difference in cytokeratin expression was noted for HPKIA-induced cysts and HPKIA-induced carcinomas. In addition to the expression of suprabasal markers such as cytokeratin 10 and involucrin, carcinomas also express cytokeratin 8 and 18. The latter cytokeratin pair is often expressed in high-grade cervical neoplasia and cervical squamous cell carcinomas. Extensive cytogenetic analyses of nontumorigenic HPKIA cells and their tumorigenic segregants has revealed no single chromosomal abnormality which is confined to all tumorigenic cells. A consistent net loss of chromosomes 3, 5, 9, 12, and 22 was evident for all malignant cells. HPKIA cells represent all stages of transformation and are thus useful for defining secondary genetic events that potentially mark malignant progression in human cells in vivo.

Hamartoma of the breast with involvement of 6p21 and rearrangement of HMGIY

The first description of involvement of 6p21 and rearrangement of HMGIY in a hamartoma of the breast is in keeping with the emerging role of HMG genes in benign mesenchymal tumors. Genes Chromosom. Cancer 20:90–92, 1997.

Mapping of the translocation breakpoints of primary pleomorphic adenomas and lipomas within a common region of chromosome 12.

Recent molecular cytogenetic analysis of uterine leiomyoma cell lines with chromosomal aberrations of 12q14-q15 have indicated that the chromosome 12 breakpoints cluster in a 445-kb region designated ULCR12 (uterine leiomyoma cluster region of the chromosome 12 breakpoints). Here we report the results of FISH studies of five primary pleomorphic adenomas and six primary lipomas and established cell lines of these tumor types characterized by translocations involving the chromosomal segment 12q13-q15. The results reveal that for nearly all tumors and cell lines analyzed, the chromosome 12 breakpoints map within a 350-kb region included in ULCR12, despite the previous cytogenetic assignment of the breakpoints to different bands of that region. In some cases the primary material and additionally analyzed cell lines allowed an even more precise localization of the breakpoints to less than 100 kb. Furthermore, a previously hidden translocation of ULCR12 in one primary tumor could be detected by FISH.

A hamartoma of the breast with an aberration of 12q mapped to the MAR region by fluorescence in situ hybridization

Cytogenetic studies of a breast adenolipoma (hamartoma) of a 58-year-old patient revealed a karyotype 46,XX,add(4)(?),add(6)(q?),der(7)t(7;12)(q11.1 or q11.2;q11 or q12),der(12). To our knowledge, this is the second report of an aberration involving 12q12-15 in a hamartoma of the breast. By FISH studies, we found this chromosome 12 translocation breakpoint to be mapping within the MAR (Multiple Aberration Region). MAR is known to be a major cluster region of chromosome 12 breakpoints of benign solid tumors such as uterine leiomyoma, lipoma, and pleomorphic salivary gland adenomas, therefore raising the possibility that the same gene is involved in hamartoma of the breast as in these three benign solid tumors.