Linda Magnusson

Fusion of the AHRR and NCOA2 genes through a recurrent translocation t(5;8)(p15;q13) in soft tissue angiofibroma results in upregulation of aryl hydrocarbon receptor target genes.

Soft tissue angiofibroma is a recently delineated tumor type of unknown cellular origin. Cytogenetic analysis of four cases showed that they shared a t(5;8)(p15;q13). In three of them it was the sole change, underlining its pathogenetic significance. FISH mapping suggested the involvement of the aryl hydrocarbon receptor repressor (AHRR) and nuclear receptor coactivator 2 (NCOA2) genes in 5p15 and 8q13, respectively. RT‐PCR revealed in‐frame AHRR/NCOA2 and NCOA2/AHHR transcripts in all four cases. Interphase FISH on paraffin‐embedded tissue from 10 further cases without cytogenetic data showed that three were positive for fusion of AHRR and NCOA2. While AHRR has never been implicated in gene fusions before, NCOA2 is the 3′‐partner in fusions with MYST3 and ETV6 in leukemias and with PAX3 and HEY1 in sarcomas. As in the previously described fusion proteins, NCOA2 contributes with its two activation domains to the AHRR/NCOA2 chimera, substituting for the repressor domain of AHRR. Because the amino terminal part of the transcription factor AHRR, responsible for the recognition of xenobiotic response elements in target genes and for heterodimerization, shows extensive homology with the aryl hydrocarbon receptor (AHR), the fusion is predicted to upregulate the AHR/ARNT signaling pathway. Indeed, global gene expression analysis showed upregulation of CYP1A1 as well as other typical target genes of this pathway, such as those encoding toll‐like receptors. Apart from providing a diagnostic marker for soft tissue angiofibroma, the results also suggest that this tumor constitutes an interesting model for evaluating the cellular effects of AHR signaling.

A novel SERPINE1-FOSB fusion gene results in transcriptional up-regulation of FOSB in pseudomyogenic haemangioendothelioma.

Pseudomyogenic haemangioendothelioma (PHE) is an intermediate malignant vascular soft tissue tumour primarily affecting children and young adults. The molecular basis of this neoplasm is unknown. We here used chromosome banding analysis, fluorescence in situ hybridization (FISH), mRNA sequencing, RT–PCR and quantitative real‐time PCR on a series of morphologically well‐characterized PHEs to show that a balanced translocation, t(7;19)(q22;q13), detected as the sole cytogenetic aberration in two cases, results in fusion of the SERPINE1 and FOSB genes. This translocation has not been observed in any other bone or soft tissue tumour. Interphase FISH on sections from eight additional PHEs identified the same SERPINE1–FOSB fusion in all cases. The role of SERPINE1, which is highly expressed in vascular cells, in this gene fusion is probably to provide a strong promoter for FOSB, which was found to be expressed at higher levels in PHEs than in other soft tissue tumours. FOSB encodes a transcription factor belonging to the FOS family of proteins, which, together with members of the JUN family of transcription factors, are major components of the activating protein 1 (AP‐1) complex. Further studies are needed to understand the cellular impact of the aberrant expression of the FOSB gene, but as the t(7;19) resulting in the SERPINE1–FOSB fusion seems to be pathognomonic for PHE, FISH or RT–PCR could be useful for differential diagnostic purposes. Published by John Wiley & Sons, Ltd. www.pathsoc.org.uk

Recurrent EWSR1-CREB3L1 gene fusions in sclerosing epithelioid fibrosarcoma.

Sclerosing epithelioid fibrosarcoma (SEF) and low-grade fibromyxoid sarcoma (LGFMS) are 2 distinct types of sarcoma, with a subset of cases showing overlapping morphologic and immunohistochemical features. LGFMS is characterized by expression of the MUC4 protein, and about 90% of cases display a distinctive FUS-CREB3L2 gene fusion. In addition, SEF is often MUC4 positive, but is genetically less well studied. Fluorescence in situ hybridization (FISH) studies have shown involvement of the FUS gene in the majority of so-called hybrid LGFMS/SEF and in 10% to 25% of sarcomas with pure SEF morphology. In this study, we investigated a series of 10 primary tumors showing pure SEF morphology, 4 cases of LGFMS that at local or distant relapse showed predominant SEF morphology, and 1 primary hybrid LGFMS/SEF. All but 1 case showed diffuse expression for MUC4. Using FISH, reverse transcription polymerase chain reaction, and/or mRNA sequencing in selected cases, we found recurrent EWSR1-CREB3L1 fusion transcripts by reverse transcription polymerase chain reaction in 3/10 pure SEF cases and splits and deletions of the EWSR1 and/or CREB3L1 genes by FISH in 6 additional cases. All 5 cases of LGFMS with progression to SEF morphology or hybrid features had FUS-CREB3L2 fusion transcripts. Our results indicate that EWSR1 and CREB3L1 rearrangements are predominant over FUS and CREB3L2 rearrangements in pure SEF, highlighting that SEF and LGFMS are different tumor types, with different impacts on patient outcome.

FUS-CREB3L2/L1-positive sarcomas show a specific gene expression profile with upregulation of CD24 and FOXL1.

Purpose: Low-grade fibromyxoid sarcoma (LGFMS) is typically characterized by the specific translocation t(7;16)(q33;p11) and the corresponding fusion gene FUS-CREB3L2. The present study aimed to extract LGFMS-specific, and putatively FUS-CREB3L2–dependent, gene expression patterns to learn more about the pathogenesis of this tumor. Experimental Design: We carried out single nucleotide polymorphism (SNP) and global gene expression array analyses, and/or immunohistochemical (IHC) analyses on 24 LGFMS tumor biopsies. Tumor types that are important differential diagnoses to LGFMS were included as comparison in the gene and protein expression analyses. In addition, cells that stably expressed FUS-CREB3L2 were analyzed with gene expression array and the influence of FUS-CREB3L2 on gene expression was investigated in vitro. Results: The SNP array analysis detected recurrent microdeletions in association with the t(7;16) chromosomal breakpoints and gain of 7q in cases with ring chromosomes. Gene expression analysis clearly distinguished LGFMS from morphologically similar tumors and MUC4 was identified as a potential diagnostic marker for LGFMS by gene expression and IHC analysis. FOXL1 was identified as the top upregulated gene in LGFMS and CD24 was upregulated in both LGFMS tumors and FUS-CREB3L2 expressing cells. FUS-CREB3L2 was capable of activating transcription from CD24 regulatory sequences in luciferase assays, suggesting an important role for the upregulation of this gene in LGFMS. Conclusions: The gene expression profile of LGFMS is distinct from that of soft tissue tumors with similar morphology. The data could be used to identify a potential diagnostic marker for LGFMS and to identify possible FUS-CREB3L2 regulated genes. Clin Cancer Res; 17(9); 2646–56. ©2011 AACR.

Concomitant deletions of tumor suppressor genes MEN1 and AIP are essential for the pathogenesis of the brown fat tumor hibernoma

Hibernomas are benign tumors with morphological features resembling brown fat. They consistently display cytogenetic rearrangements, typically translocations, involving chromosome band 11q13. Here we demonstrate that these aberrations are associated with concomitant deletions of AIP and MEN1, tumor suppressor genes that are located 3 Mb apart and that underlie the hereditary syndromes pituitary adenoma predisposition and multiple endocrine neoplasia type I. MEN1 and AIP displayed a low expression in hibernomas whereas the expression of genes up-regulated in brown fat—PPARA, PPARG, PPARGC1A, and UCP1—was high. Thus, loss of MEN1 and AIP is likely to be pathogenetically essential for hibernoma development. Simultaneous loss of two tumor suppressor genes has not previously been shown to result from a neoplasia-associated translocation. Furthermore, in contrast to the prevailing assumption that benign tumors harbor relatively few genetic aberrations, the present analyses demonstrate that a considerable number of chromosome breaks are involved in the pathogenesis of hibernoma.

A novel GTF2I/NCOA2 fusion gene emphasizes the role of NCOA2 in soft tissue angiofibroma development.

Soft tissue angiofibroma is a recently described benign fibrovascular tumor of unknown cellular origin (Mariño-Enrı́quez and Fletcher, 2012). We reported, in this journal, that the t(5;8)(p15;q13) is a recurrent cytogenetic feature in this tumor type and that it results in the formation of a novel, and so far tumor-specific, fusion of the two transcription-associated genes AHRR in 5p15 and NCOA2 in 8q13 (Jin et al., 2012). An unexpected finding was that all four cases that could be analyzed by reverse transcription PCR (RT-PCR) expressed in-frame fusion transcripts from both derivate chromosomes, i.e., both AHRR/NCOA2 and NCOA2/AHRR. Furthermore, by interphase fluorescence in situ hybridization (FISH) analysis of tumor sections, we showed that a substantial subset of soft tissue angiofibromas is negative for the fusion gene. Here, we report the finding of an alternative fusion gene—GTF2I/NCOA2—in a new case of soft tissue angiofibroma, thereby demonstrating that this tumor type is associated with more than one fusion gene and that it is the transcripts in which NCOA2 is the 30 partner that are pathogenetically relevant. The patient was a 41-year-old woman with a tumor in the thigh. The lesion was first diagnosed as a myxofibrosarcoma but further histopathologic and immunohistochemical analyses, prompted by the cytogenetic finding of a t(7;8;14)(q11;q13;q31) as the sole change, disclosed that it was a soft tissue angiofibroma. Metaphase FISH was carried out on metaphase preparations using a previously described break-apart probe for NCOA2 in 8q13 (Jin et al., 2012). This analysis showed that the NCOA2 gene was rearranged, with one signal on the derivative chromosome 7 and one on the derivative chromosome 8. The 7q11 breakpoint was then mapped with a series of bacterial artificial chromosome (BAC) and fosmid probes, revealing a complex rearrangement of chromosome 7 that involved at least three different breakpoints (Table 1). One of the breakpoint regions covered a single gene— GTF2I—that was further analyzed using RT-PCR. Conventional, nested, and semi-nested RTPCR analysis of extracted total RNA, using GTF2I-1214F (50-GGCAATGAAGGCACAGAA AT), GTF2I-2083F (50-CTTGCAACCCTGAAA TGGAT), NCOA2-3807R (30-GCCTCAGAGTCAAGTTCACA), and NCOA2-3332R (30-CAAG TCATCTGGAGAACTGC) primers in all possible combinations resulted in four fragments— amplified by nested PCR using GTF2I-2083F and NCOA2-3332R—varying in size from 150 to 300 bp (Fig. 1A). Sequencing was performed using GTF2I 2083F and NCOA2 3332R. Sequence analyses were unsuccessful for the two smaller bands. However, the two larger bands were 256 and 221 bp sequences that corresponded to two splicing variants of a GTF2I/NCOA2 chimeric transcript. The 256 bp fragment corresponded to an in-frame fusion of part of exon 14 of GTF2I with part of exon 15 of NCOA2 whereas the 221 bp sequence was an outof-frame fusion of part of exon 11 of GTF2I with part of exon 14 of NCOA2 (Fig. 1B). Thus, a GTF2I/NCOA2 fusion transcript was confirmed. The finding of a new alternative 50 partner for NCOA2 suggests that regulatory sequences in NCOA2 have a primary role in the pathogenesis of soft tissue angiofibromas. GTF2I, a multifunctional DNA-binding transcription factor involved primarily TABLE 1. Results of FISH Analysis of the Breakpoint in 7q in a Soft Tissue Angiofibroma with t(7;8;14)

The Retinoblastoma Gene Undergoes Rearrangements in BRCA1-Deficient Basal-like Breast Cancer

Breast tumors from BRCA1 germ line mutation carriers typically exhibit features of the basal-like molecular subtype. However, the specific genes recurrently mutated as a consequence of BRCA1 dysfunction have not been fully elucidated. In this study, we used gene expression profiling to molecularly subtype 577 breast tumors, including 73 breast tumors from BRCA1/2 mutation carriers. Focusing on the RB1 locus, we analyzed 33 BRCA1-mutated, 36 BRCA2-mutated, and 48 non-BRCA1/2-mutated breast tumors using a custom-designed high-density oligomicroarray covering the RB1 gene. We found a strong association between the basal-like subtype and BRCA1-mutated breast tumors and the luminal B subtype and BRCA2-mutated breast tumors. RB1 was identified as a major target for genomic disruption in tumors arising in BRCA1 mutation carriers and in sporadic tumors with BRCA1 promoter methylation but rarely in other breast cancers. Homozygous deletions, intragenic breaks, or microdeletions were found in 33% of BRCA1-mutant tumors, 36% of BRCA1 promoter-methylated basal-like tumors, 13% of non-BRCA1-deficient basal-like tumors, and 3% of BRCA2-mutated tumors. In conclusion, RB1 was frequently inactivated by gross gene disruption in BRCA1 hereditary breast cancer and BRCA1-methylated sporadic basal-like breast cancer but rarely in BRCA2 hereditary breast cancer and non-BRCA1-deficient sporadic breast cancers. Together, our findings show the existence of genetic heterogeneity within the basal-like breast cancer subtype that is based upon BRCA1 status.

GRM1 is upregulated through gene fusion and promoter swapping in chondromyxoid fibroma

Glutamate receptors are well-known actors in the central and peripheral nervous systems, and altered glutamate signaling is implicated in several neurological and psychiatric disorders. It is increasingly recognized that such receptors may also have a role in tumor growth. Here we provide direct evidence of aberrant glutamate signaling in the development of a locally aggressive bone tumor, chondromyxoid fibroma (CMF). We subjected a series of CMFs to whole-genome mate-pair sequencing and RNA sequencing and found that the glutamate receptor gene GRM1 recombines with several partner genes through promoter swapping and gene fusion events. The GRM1 coding region remains intact, and 18 of 20 CMFs (90%) showed a more than 100-fold and up to 1,400-fold increase in GRM1 expression levels compared to control tissues. Our findings unequivocally demonstrate that direct targeting of GRM1 is a necessary and highly specific driver event for CMF development.

Gene fusion detection in formalin-fixed paraffin-embedded benign fibrous histiocytomas using fluorescence in situ hybridization and RNA sequencing

Benign fibrous histiocytomas (FH) can be subdivided into several morphological and clinical subgroups. Recently, gene fusions involving either one of two protein kinase C genes (PRKCB and PRKCD) or the ALK gene were described in FH. We here wanted to evaluate the frequency of PRKCB and PRKCD gene fusions in FH. Using interphase fluorescence in situ hybridization on sections from formalin-fixed paraffin-embedded (FFPE) tumors, 36 cases could be analyzed. PRKCB or PRKCD rearrangements were seen in five tumors: 1/7 regular, 0/3 aneurysmal, 0/6 cellular, 2/7 epithelioid, 0/1 atypical, 2/10 deep, and 0/2 metastatic lesions. We also evaluated the status of the ALK gene in selected cases, finding rearrangements in 3/7 epithelioid and 0/1 atypical lesions. To assess the gene fusion status of FH further, deep sequencing of RNA (RNA-Seq) was performed on FFPE tissue from eight cases with unknown gene fusion status, as well as on two FH and six soft tissue sarcomas with known gene fusions; of the latter eight positive controls, the expected fusion transcript was found in all but one, while 2/8 FH with unknown genetic status showed fusion transcripts, including a novel KIRREL/PRKCA chimera. Thus, also a third member of the PRKC family is involved in FH tumorigenesis. We conclude that gene fusions involving PRKC genes occur in several morphological (regular, cellular, aneurysmal, epithelioid) and clinical (cutaneous, deep) subsets of FH, but they seem to account for only a minority of the cases. In epithelioid lesions, however, rearrangements of PRKC or ALK were seen, as mutually exclusive events, in the majority (5/7) of cases. Finally, the study also shows that RNA-Seq is a promising tool for identifying gene fusions in FFPE tissues.

Fusions involving protein kinase C and membrane-associated proteins in benign fibrous histiocytoma

Benign fibrous histiocytoma (BFH) is a mesenchymal tumor that most often occurs in the skin (so-called dermatofibroma), but may also appear in soft tissues (so-called deep BFH) and in the skeleton (so-called non-ossifying fibroma). The origin of BFH is unknown, and it has been questioned whether it is a true neoplasm. Chromosome banding, fluorescence in situ hybridization, single nucleotide polymorphism arrays, RNA sequencing, RT-PCR and quantitative real-time PCR were used to search for recurrent somatic mutations in a series of BFH. BFHs were found to harbor recurrent fusions of genes encoding membrane-associated proteins (podoplanin, CD63 and LAMTOR1) with genes encoding protein kinase C (PKC) isoforms PRKCB and PRKCD. PKCs are serine-threonine kinases that through their many phosphorylation targets are implicated in a variety of cellular processes, as well as tumor development. When inactive, the amino-terminal, regulatory domain of PKCs suppresses the activity of their catalytic domain. Upon activation, which requires several steps, they typically translocate to cell membranes, where they interact with different signaling pathways. The detected PDPN-PRKCB, CD63-PRKCD and LAMTOR1-PRKCD gene fusions are all predicted to result in chimeric proteins consisting of the membrane-binding part of PDPN, CD63 or LAMTOR1 and the entire catalytic domain of the PKC. This novel pathogenetic mechanism should result in constitutive kinase activity at an ectopic location. The results show that BFH indeed is a true neoplasm, and that distorted PKC activity is essential for tumorigenesis. The findings also provide means to differentiate BFH from other skin and soft tissue tumors. This article is part of a Directed Issue entitled: Rare cancers.