Fusion of the HMGA2 and NFIB genes in lipoma

Non-gastrointestinal stromal tumor, mesenchymal neoplasms of the gastrointestinal tract: a review of tumor genetics, pathology, and cross-sectional imaging findings

There is a diverse group of non-gastrointestinal stromal tumor (GIST), mesenchymal neoplasms of the gastrointestinal (GI) tract that demonstrate characteristic pathology and histogenesis as well as variable imaging findings and biological behavior. Recent advancements in tumor genetics have unveiled specific abnormalities associated with certain tumors, influencing their molecular pathogenesis, biology, response to treatment, and prognosis. Notably, giant fibrovascular polyps of the esophagus, identified through MDM2 gene amplifications, are now classified as liposarcomas. Some tumors exhibit distinctive patterns of disease distribution. Glomus tumors and plexiform fibromyxomas exhibit a pronounced affinity for the gastric antrum. In contrast, smooth muscle tumors within the GI tract are predominantly found in the esophagus and colorectum, surpassing the incidence of GISTs in these locations. Surgical resection suffices for symptomatic benign tumors; multimodality treatment may be necessary for frank sarcomas. This article aims to elucidate the cross-sectional imaging findings associated with a wide spectrum of these tumors, providing insights that align with their histopathological features.

Familial multiple lipomatosis associated with multiple cherry hemangiomas and moles: a rare case report

Lipomas are common benign mesenchymal tumours, whereas lipomatoses are uncommon. Familial multiple lipomatosis (FML) is a rare syndrome characterized by multiple usually painless lipomas which may be associated with other conditions. FML is considered to be genetic, with various patterns of inheritance suggested. In this case report, we described a case of multiple familial lipomatosis that was misdiagnosed as dercum's disease.

Treatment of De-Differentiated Liposarcoma in the Era of Immunotherapy

Well-differentiated/de-differentiated liposarcoma (WDLPS/DDLPS) is one of the most common histologic subtypes of soft tissue sarcoma (STS); however, treatment options remain limited. WDLPS and DDLPS both exhibit the characteristic amplification of chromosome region 12q13-15, which contains the genes CDK4 and MDM2. DDLPS exhibits higher amplification ratios of these two and carries additional genomic lesions, including the amplification of chromosome region 1p32 and chromosome region 6q23, which may explain the more aggressive biology of DDLPS. WDLPS does not respond to systemic chemotherapy and is primarily managed with local therapy, including multiple resections and debulking procedures whenever clinically feasible. In contrast, DDLPS can respond to chemotherapy drugs and drug combinations, including doxorubicin (or doxorubicin in combination with ifosfamide), gemcitabine (or gemcitabine in combination with docetaxel), trabectedin, eribulin, and pazopanib. However, the response rate is generally low, and the response duration is usually short. This review highlights the clinical trials with developmental therapeutics that have been completed or are ongoing, including CDK4/6 inhibitors, MDM2 inhibitors, and immune checkpoint inhibitors. This review will also discuss the current landscape in assessing biomarkers for identifying tumors sensitive to immune checkpoint inhibitors.

Neoplasia-associated Chromosome Translocations Resulting in Gene Truncation

Chromosomal translocations in cancer as well as benign neoplasias typically lead to the formation of fusion genes. Such genes may encode chimeric proteins when two protein-coding regions fuse in-frame, or they may result in deregulation of genes via promoter swapping or translocation of the gene into the vicinity of a highly active regulatory element. A less studied consequence of chromosomal translocations is the fusion of two breakpoint genes resulting in an out-of-frame chimera. The breaks then occur in one or both protein-coding regions forming a stop codon in the chimeric transcript shortly after the fusion point. Though the latter genetic events and mechanisms at first awoke little research interest, careful investigations have established them as neither rare nor inconsequential. In the present work, we review and discuss the truncation of genes in neoplastic cells resulting from chromosomal rearrangements, especially from seemingly balanced translocations.

Recurrent Fusion of the Genes for High-mobility Group AT-hook 2 (HMGA2) and Nuclear Receptor Co-repressor 2 (NCOR2) in Osteoclastic Giant Cell-rich Tumors of Bone

BACKGROUND/AIM

Chimeras involving the high-mobility group AT-hook 2 gene (HMGA2 in 12q14.3) have been found in lipomas and other benign mesenchymal tumors. We report here a fusion of HMGA2 with the nuclear receptor co-repressor 2 gene (NCOR2 in 12q24.31) repeatedly found in tumors of bone and the first cytogenetic investigation of this fusion.

MATERIALS AND METHODS

Six osteoclastic giant cell-rich tumors were investigated using G-banding, RNA sequencing, reverse transcription polymerase chain reaction, Sanger sequencing, and fluorescence in situ hybridization.

RESULTS

Four tumors had structural chromosomal aberrations of 12q. The pathogenic variant c.103_104GG>AT (p.Gly35Met) in the H3.3 histone A gene was found in a tumor without 12q aberration. In-frame HMGA2-NCOR2 fusion transcripts were found in all tumors. In two cases, the presence of an HMGA2-NCOR2 fusion gene was confirmed by FISH on metaphase spreads.

CONCLUSION

Our results demonstrate that a subset of osteoclastic giant cell-rich tumors of bone are characterized by an HMGA2-NCOR2 fusion gene.

Reduced lipolysis in lipoma phenocopies lipid accumulation in obesity

BACKGROUND

Elucidation of lipid metabolism and accumulation mechanisms is of paramount importance to understanding obesity and unveiling therapeutic targets. In vitro cell models have been extensively used for these purposes, yet, they do not entirely reflect the in vivo setup. Conventional lipomas, characterized by the presence of mature adipocytes and increased adipogenesis, could overcome the drawbacks of cell cultures. Also, they have the unique advantage of easily accessible matched controls in the form of subcutaneous adipose tissue (SAT) from the same individual. We aimed to determine whether lipomas are a good model to understand lipid accumulation.

METHODS

We histologically compared lipomas and control SAT, followed by assessment of the lipidome using high-resolution ¹H NMR spectroscopy and ESI-IT mass spectrometry. RNA-sequencing was used to obtain the transcriptome of lipomas and the matched SAT.

RESULTS

We found a significant increase of small-size (maximal axis < 70 µm) and very big (maximal axis > 150 µm) adipocytes within lipomas. This suggests both enhanced adipocyte proliferation and increased lipid accumulation. We further show that there is no significant change in the lipid composition compared to matched SAT. To better delineate the pathophysiology of lipid accumulation, we considered two groups with different genetic backgrounds: (1) lipomas with HMGA2 fusions and (2) without gene fusions. To reduce the search space for genes that are relevant for lipid pathophysiology, we focused on the overlapping differentially expressed (DE) genes between the two groups. Gene Ontology analysis revealed that DE genes are enriched in pathways related to lipid accumulation.

CONCLUSIONS

We show that the common shared lipid accumulation mechanism in lipoma is a reduction in lipolysis, with most gene dysregulations leading to a reduced cAMP in the adipocyte. Superficial lipomas could thus be used as a model for lipid accumulation through altered lipolysis as found in obese patients.

Frequent activating PIK3CA mutations in sporadic angiolipoma

BACKGROUND

Angiolipoma (AL) is considered as a lipoma variant that is characterized by the combination of mature adipocytes and capillary blood vessels diffusely distributed within the tumor. With the exception of recurrent PRKD2 mutations of uncertain pathogenetic significance, the genetic abnormalities of ALs are unknown, in the absence of any of the specific chromosomal aberrations described in other lipoma variants.

METHODS

Formalin-fixed and paraffin-embedded blocks of 13 conventional ALs and 5 cellular ALs from 17 individuals were retrieved and analyzed for mutations in exons 9 and 20 of PIK3CA by polymerase chain reaction and Sanger sequencing.

RESULTS

Activating PIK3CA mutations were identified in 14 tumors (78%). All PIK3CA-mutated samples carried the same exon 9 mutation, c.1634A>C (p.E545A). No mutation was detected in exon 20 of PIK3CA. No significant difference between PIK3CA-mutated and wild-type samples appeared to exist based on age, gender, and location of the tumor. All 5 cellular ALs carried the p.E545A PIK3CA mutation.

CONCLUSION

The high frequency of the p.E545A PIK3CA mutation in both conventional and cellular ALs suggests that activation of the PI3K/AKT pathway plays a key role in AL pathogenesis and reinforces the concept that cellular AL should be regarded as a variant of AL.

High HMGA2 expression without gene rearrangement in meningiomas

High mobility group AT-hook 2 (HMGA2) is a non-histone transcriptional regulator protein. Aberrant expression of the HMGA2 gene (HMGA2) and structural rearrangement at the chromosomal region 12q14 with HMGA2 involvement have been reported in several mesenchymal tumors. We analyzed truncated and full-length HMGA2 expression in 55 cases of meningioma, the most common brain tumor of mesenchymal origin. Fluorescence in situ hybridization and 3'-rapid amplification of cDNA ends were used to investigate the possibility of gene rearrangements. Moreover, the relationship between HMGA2 expression and clinicopathological features was assessed. Compared with normal brain tissues, 95% of the meningioma tissues exhibited increased HMGA2 expression. In 14 cases, the expression of truncated HMGA2 was more than two-fold higher than that of paired full-length HMGA2. Chromosomal translocation involving the chromosomal region 12q14 was undetectable. No significant correlation was found between the Ki-67 labeling index and HMGA2 expression and between the HMGA2 expression and the clinicopathological features. The majority of the meningioma cases displayed increased HMGA2 expression, which was not attributed to the chromosomal rearrangement at the corresponding region. Similar to that in the other mesenchymal tumors, increased HMGA2 expression was not associated with tumor cell proliferation in meningiomas.

Activation of PLAG1 and HMGA2 by gene fusions involving the transcriptional regulator gene NFIB

The pleomorphic adenoma (PA), which is the most common salivary gland neoplasm, is a benign tumor characterized by recurrent chromosome rearrangements involving 8q12 and 12q14-15. We have previously shown that the PLAG1 and HMGA2 oncogenes are the targets of these rearrangements. Here, we have identified previously unrecognized subsets of PAs with ins(9;8)/t(8;9) (n = 5) and ins(9;12)/t(9;12) (n = 8) and breakpoints located in the vicinity of the PLAG1 and HMGA2 loci. RNA-sequencing and reverse transcriptase (RT)-PCR analyses of a case with an ins(9;8) revealed a novel NFIB-PLAG1 fusion in which NFIB exon 4 is linked to PLAG1 exon 3. In contrast to the developmentally regulated PLAG1 gene, NFIB was highly expressed in normal salivary gland, indicating that PLAG1 in this case, as in other variant fusions, is activated by promoter swapping. RT-PCR analysis of three PAs with t(9;12) revealed two tumors with chimeric transcripts consisting of HMGA2 exon 4 linked to NFIB exons 9 or 3 and one case with a fusion linking HMGA2 exon 3 to NFIB exon 9. The NFIB fusion events resulted in potent activation of PLAG1 and HMGA2. Analysis of the chromatin landscape surrounding NFIB revealed several super-enhancers in the 5'- and 3'-parts of the NFIB locus and its flanking sequences. These findings indicate that PLAG1 and HMGA2, similar to MYB in adenoid cystic carcinoma, may be activated by enhancer-hijacking events, in which super-enhancers in NFIB are translocated upstream of PLAG1 or downstream of HMGA2. Our results further emphasize the role of NFIB as a fusion partner to multiple oncogenes in histopathologically different types of salivary gland tumors.

High Mobility Group AT-Hook 2 (HMGA2) Oncogenicity in Mesenchymal and Epithelial Neoplasia

High mobility group AT-hook 2 (HMGA2) has been associated with increased cell proliferation and cell cycle dysregulation, leading to the ontogeny of varied tumor types and their metastatic potentials, a frequently used index of disease prognosis. In this review, we deepen our understanding of HMGA2 pathogenicity by exploring the mechanisms by which HMGA2 misexpression and ectopic expression induces mesenchymal and epithelial tumorigenesis respectively and distinguish the pathogenesis of benign from malignant mesenchymal tumors. Importantly, we highlight the regulatory role of let-7 microRNA family of tumor suppressors in determining HMGA2 misexpression events leading to tumor pathogenesis and focused on possible mechanisms by which HMGA2 could propagate lymphangioleiomyomatosis (LAM), benign mesenchymal tumors of the lungs. Lastly, we discuss potential therapeutic strategies for epithelial and mesenchymal tumorigenesis based on targeting the HMGA2 signaling pathway.

Adenoid cystic carcinoma: emerging role of translocations and gene fusions

Adenoid cystic carcinoma (ACC), the second most common salivary gland malignancy, is notorious for poor prognosis, which reflects the propensity of ACC to progress to clinically advanced metastatic disease. Due to high long-term mortality and lack of effective systemic treatment, the slow-growing but aggressive ACC poses a particular challenge in head and neck oncology. Despite the advancements in cancer genomics, up until recently relatively few genetic alterations critical to the ACC development have been recognized. Although the specific chromosomal translocations resulting in MYB-NFIB fusions provide insight into the ACC pathogenesis and represent attractive diagnostic and therapeutic targets, their clinical significance is unclear, and a substantial subset of ACCs do not harbor the MYB-NFIB translocation. Strategies based on detection of newly described genetic events (such as MYB activating super-enhancer translocations and alterations affecting another member of MYB transcription factor family-MYBL1) offer new hope for improved risk assessment, therapeutic intervention and tumor surveillance. However, the impact of these approaches is still limited by an incomplete understanding of the ACC biology, and the manner by which these alterations initiate and drive ACC remains to be delineated. This manuscript summarizes the current status of gene fusions and other driver genetic alterations in ACC pathogenesis and discusses new therapeutic strategies stemming from the current research.

A rare case of pediatric lipoma with t(9;12)(p22;q14) and evidence of HMGA2-NFIB gene fusion

Lipoma is a benign tumor, typically of adulthood, with characteristic cytogenetic findings, including rearrangement of 12q13-15; these rearrangements often lead to the fusion of the HMGA2 gene at this locus to the transcriptional regulatory domain of its fusion partner, resulting in neomorphic activity that presumably facilitates the neoplastic process. Herein, we report a rare case of pediatric lipoma with t(9;12)(p22;q14) and evidence of HMGA2-NFIB gene fusion in a 9 year-old boy. This case provides further evidence of the link between NFIB rearrangement and early-onset, deep-seated lipomatous tumors.

The convergent roles of the nuclear factor I transcription factors in development and cancer

The nuclear factor I (NFI) transcription factors play important roles during normal development and have been associated with developmental abnormalities in humans. All four family members, NFIA, NFIB, NFIC and NFIX, have a homologous DNA binding domain and function by regulating cell proliferation and differentiation via the transcriptional control of their target genes. More recently, NFI genes have also been implicated in cancer based on genomic analyses and studies of animal models in a variety of tumours across multiple organ systems. However, the association between their functions in development and in cancer is not well described. In this review, we summarise the evidence suggesting a converging role for the NFI genes in development and cancer. Our review includes all cancer types in which the NFI genes are implicated, focusing predominantly on studies demonstrating their oncogenic or tumour-suppressive potential. We conclude by presenting the challenges impeding our understanding of NFI function in cancer biology, and demonstrate how a developmental perspective may contribute towards overcoming such hurdles.

Fusion of the HMGA2 and C9orf92 genes in myolipoma with t(9;12)(p22;q14)

Background

Myolipoma of soft tissue is an extremely rare benign tumor composed of mature adipose tissue and smooth muscle cells. It is found predominantly in women. The cytogenetic and molecular genetic features of myolipomas remain largely unexplored. Here we present the first cytogenetically analyzed myolipoma.

Methods

Cytogenetic and molecular genetic analyses were done on a myolipoma.

Results

G-banding analysis of short-term cultured cells from the myolipoma yielded a karyotype with a single clonal chromosome abnormality: 46,XX,t(9;12)(p22;q14). Fluorescence in situ hybridization experiments demonstrated that HMGA2 (in 12q14) was rearranged. Molecular genetic analysis showed that the translocation resulted in fusion of HMGA2 with the C9orf92 gene (from 9p22). The HMGA2-C9orf92 fusion transcript would code for a putative protein containing amino acid residues 1–94 of HMGA2 and 6 amino acid residues from the out-of-frame fusion with exon 4 of C9orf92.

Conclusion

The pattern of HMGA2 rearrangement in the present case of myolipoma is similar to what is found in other benign connective tissue tumor types, including lipomas, i.e., disruption of the HMGA2 locus leaves intact exons which encode the AT-hook domains but separates them from the 3´-terminal part of the gene. Whether any genetic features differentiate myolipomas from regular lipomas with HMGA2-involvement is a question that cannot be answered until more cases of the former tumor type are subjected to genetic analysis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13000-016-0472-8) contains supplementary material, which is available to authorized users.

Gene fusions in soft tissue tumors: Recurrent and overlapping pathogenetic themes

Gene fusions have been described in approximately one-third of soft tissue tumors (STT); of the 142 different fusions that have been reported, more than half are recurrent in the same histologic subtype. These gene fusions constitute pivotal driver mutations, and detailed studies of their cellular effects have provided important knowledge about pathogenetic mechanisms in STT. Furthermore, most fusions are strongly associated with a particular histotype, serving as ideal molecular diagnostic markers. In recent years, it has also become apparent that some chimeric proteins, directly or indirectly, constitute excellent treatment targets, making the detection of gene fusions in STT ever more important. Indeed, pharmacological treatment of STT displaying fusions that activate protein kinases, such as ALK and ROS1, or growth factors, such as PDGFB, is already in clinical use. However, the vast majority (52/78) of recurrent gene fusions create structurally altered and/or deregulated transcription factors, and a small but growing subset develops through rearranged chromatin regulators. The present review provides an overview of the spectrum of currently recognized gene fusions in STT, and, on the basis of the protein class involved, the mechanisms by which they exert their oncogenic effect are discussed.

A unifying gene signature for adenoid cystic cancer identifies parallel MYB-dependent and MYB-independent therapeutic targets

MYB activation is proposed to underlie development of adenoid cystic cancer (ACC), an aggressive salivary gland tumor with no effective systemic treatments. To discover druggable targets for ACC, we performed global mRNA/miRNA analyses of 12 ACC with matched normal tissues, and compared these data with 14 mucoepidermoid carcinomas (MEC) and 11 salivary adenocarcinomas (ADC). We detected a unique ACC gene signature of 1160 mRNAs and 22 miRNAs. MYB was the top-scoring gene (18-fold induction), however we observed the same signature in ACC without detectable MYB gene rearrangements. We also found 4 ACC tumors (1 among our 12 cases and 3 from public databases) with negligible MYB expression that retained the same ACC mRNA signature including over-expression of extracellular matrix (ECM) genes. Integration of this signature with somatic mutational analyses suggests that NOTCH1 and RUNX1 participate with MYB to activate ECM elements including the VCAN/HAPLN1 complex. We observed that forced MYB-NFIB expression in human salivary gland cells alters cell morphology and cell adhesion in vitro and depletion of VCAN blocked tumor cell growth of a short-term ACC tumor culture. In summary, we identified a unique ACC signature with parallel MYB-dependent and independent biomarkers and identified VCAN/HAPLN1 complexes as a potential target.

The recurrent chromosomal translocation t(12;18)(q14~15;q12~21) causes the fusion gene HMGA2-SETBP1 and HMGA2 expression in lipoma and osteochondrolipoma

Lipomas are the most common soft tissue tumors in adults. They often carry chromosome aberrations involving 12q13~15 leading to rearrangements of the HMGA2 gene in 12q14.3, with breakpoints occurring within or outside of the gene. Here, we present eleven lipomas and one osteochondrolipoma with a novel recurrent chromosome aberration, t(12;18) (q14~15;q12~21). Molecular studies on eight of the tumors showed that full-length HMGA2 transcript was expressed in three and a chimeric HMGA2 transcript in five of them. In three lipomas and in the osteochondrolipoma, exons 1–3 of HMGA2 were fused to a sequence of SETBP1 on 18q12.3 or an intragenic sequence from 18q12.3 circa 10 kbp distal to SETBP1. In another lipoma, exons 1–4 of HMGA2 were fused to an intronic sequence of GRIP1 which maps to chromosome band 12q14.3, distal to HMGA2. The ensuing HMGA2 fusion transcripts code for putative proteins which contain amino acid residues of HMGA2 corresponding to exons 1–3 (or exons 1–4 in one case) followed by amino acid residues corresponding to the fused sequences. Thus, the pattern is similar to the rearrangements of HMGA2 found in other lipomas, i.e., disruption of the HMGA2 locus leaves intact exons 1–3 which encode the AT-hooks domains and separates them from the 3′-terminal part of the gene. The fact that the examined osteochondrolipoma had a t(12;18) and a HMGA2-SETBP1 fusion identical to the findings in the much more common ordinary lipomas, underscores the close developmental relationship between the two tumor types.

Identification of PPAP2B as a novel recurrent translocation partner gene of HMGA2 in lipomas

Most lipomas are characterized by translocations involving the HMGA2 gene in 12q14.3. These rearrangements lead to the fusion of HMGA2 with an ectopic sequence from the translocation chromosome partner. Only five fusion partners of HMGA2 have been identified in lipomas so far. The identification of novel fusion partners of HMGA2 is important not only for diagnosis in soft tissue tumors but also because these genes might have an oncogenic role in other tumors. We observed that t(1;12)(p32;q14) was the second most frequent translocation in our series of lipomas after t(3;12)(q28;q14.3). We detected overexpression of HMGA2 mRNA and protein in all t(1;12)(p32;q14) lipomas. We used a fluorescence in situ hybridization-based positional cloning strategy to characterize the 1p32 breakpoint. In 11 cases, we identified PPAP2B, a member of the lipid phosphate phosphatases family as the 1p32 target gene. Reverse transcription-polymerase chain reaction analysis followed by nucleotide sequencing of the fusion transcript indicated that HMGA2 3' untranslated region (3'UTR) fused with exon 6 of PPAP2B in one case. In other t(1;12) cases, the breakpoint was extragenic, located in the 3'region flanking PPAP2B 3'UTR. Moreover, in one case showing a t(1;6)(p32;p21) we observed a rearrangement of PPAP2B and HMGA1, which suggests that HMGA1 might also be a fusion partner for PPAP2B. Our results also revealed that adipocytic differentiation of human mesenchymal stem cells derived from adipose tissue was associated with a significant decrease in PPAP2B mRNA expression suggesting that PPAP2B might play a role in adipogenesis.

NFIB is a potential target for estrogen receptor-negative breast cancers

BACKGROUND

The association between nuclear factor I/B (NFIB) gene and triple negative breast cancer has been previously suggested.

METHODS

We investigated the relationship between NFIB mRNA and protein expression and molecular subtypes of breast cancer as well as the effect of NFIB silencing on the proliferation and apoptosis of breast cancer cells. Also, the clinical importance of NFIB expression was investigated in 163 breast cancer patients.

RESULTS

By using 20 frozen human breast cancer tissues and various breast cancer cell lines, we observed a significant high level of NFIB mRNA level in triple negative breast cancer. NFIB protein was upregulated in ER negative breast cancer tissues but the expression level was similar between HER2 subtype and triple negative subtype. The clinical significance of NFIB was further examined in a tissue microarray from 163 invasive breast cancer patients, and the immunohistochemistry results showed a significant association between NFIB expression and nuclear grade, ER, and HER2 expression status. NFIB positive tumors were more likely to have high nuclear grade, ER negativity and HER2 over-expression. HCC1954 cells transfected with siRNA against NFIB showed a significant reduction in cell proliferation and increase in apoptotic signaling pathway.

CONCLUSIONS

Our results show a potential role of NFIB as a novel target in ER negative breast cancers.

Chromosomal aberrations in solid tumors

Ever since the identification of the exact number of human chromosomes in 1956, several cancer-specific chromosomal abnormalities have been identified in different tumors. Among the various genetic changes, such as alterations in oncogenes, tumor suppressor genes, and microRNA genes, recurrent chromosome translocations have been identified as an important class of mutations in hematological malignancies, soft tissue sarcomas, and more recently in prostate cancer and lung cancer. Recurrent gene fusions are used for cancer classification and as diagnostic markers, and some have been successfully targeted for drug development. Recent advances in high-throughput sequencing technology and the ambitious undertaking of "The Cancer Genome Atlas" (TCGA) project will help drive the identification of the underlying genetic aberrations in most of the solid cancers. This chapter presents an overview on the current status of the knowledge on chromosome aberrations in solid cancers, cytogenetic and noncytogenetic methods for the characterization of changes at the DNA and RNA levels, technological advancements in high-throughput characterization of the cancer genome and transcriptome, and the current understanding of the molecular mechanism involved in the formation of gene fusions in solid cancer.

Cell Adhesion and Transcriptional Activity - Defining the Role of the Novel Protooncogene LPP

Integrating signals from the extracellular matrix through the cell surface into the nucleus is an essential feature of metazoan life. To date, many signal transducers known as shuttle proteins have been identified to act as both a cytoskeletal and a signaling protein. Among them, the most prominent representatives are zyxin and lipoma preferred (translocation) partner (LPP). These proteins belong to the LIM domain protein family and are associated with cell migration, proliferation, and transcription. LPP was first identified in benign human lipomas and was subsequently found to be overexpressed in human malignancies such as lung carcinoma, soft tissue sarcoma, and leukemia. This review portrays LPP in the context of human neoplasia based on a study of the literature to define its important role as a novel protooncogene in carcinogenesis.

Molecular discrimination of cutaneous squamous cell carcinoma from actinic keratosis and normal skin

Actinic keratosis is widely believed to be a neoplastic lesion and a precursor to invasive squamous cell carcinoma. However, there has been some debate as to whether actinic keratosis is in fact actually squamous cell carcinoma and should be treated as such. As the clinical management and prognosis of patients is widely held to be different for each of these lesions, our goal was to identify unique gene signatures using DNA microarrays to discriminate among normal skin, actinic keratosis, and squamous cell carcinoma, and examine the molecular pathways of carcinogenesis involved in the progression from normal skin to squamous cell carcinoma. Formalin-fixed and paraffin-embedded blocks of skin: five normal skins (pooled), six actinic keratoses, and six squamous cell carcinomas were retrieved. The RNA was extracted and amplified. The labeled targets were hybridized to the Affymetrix human U133plus2.0 array and the acquisition and initial quantification of array images were performed using the GCOS (Affymetrix). The subsequent data analyses were performed using DNA-Chip Analyzer and Partek Genomic Suite 6.4. Significant differential gene expression (>2 fold change, P<0.05) was seen with 382 differentially expressed genes between squamous cell carcinoma and normal skin, 423 differentially expressed genes between actinic keratosis and normal skin, and 9 differentially expressed genes between actinic keratosis and squamous cell carcinoma. The differentially expressed genes offer the possibility of using DNA microarrays as a molecular diagnostic tool to distinguish between normal skin, actinic keratosis, and squamous cell carcinoma. In addition, the differentially expressed genes and their molecular pathways could be potentially used as prognostic markers or targets for future therapeutic innovations.

Contributions of cytogenetics and molecular cytogenetics to the diagnosis of adipocytic tumors

Over the last 20 years, a number of tumor-specific chromosomal translocations and associated fusion genes have been identified for mesenchymal neoplasms including adipocytic tumors. The addition of molecular cytogenetic techniques, especially fluorescence in situ hybridization (FISH), has further enhanced the sensitivity and accuracy of detecting nonrandom chromosomal translocations and/or other rearrangements in adipocytic tumors. Indeed, most resent molecular cytogenetic analysis has demonstrated a translocation t(11;16)(q13;p13) that produces a C11orf95-MKL2 fusion gene in chondroid lipoma. Additionally, it is well recognized that supernumerary ring and/or giant rod chromosomes are characteristic for atypical lipomatous tumor/well-differentiated liposarcoma and dedifferentiated liposarcoma, and amplification of 12q13–15 involving the MDM2, CDK4, and CPM genes is shown by FISH in these tumors. Moreover, myxoid/round cell liposarcoma is characterized by a translocation t(12;16)(q13;p11) that fuses the DDIT3 and FUS genes. This paper provides an overview of the role of conventional cytogenetics and molecular cytogenetics in the diagnosis of adipocytic tumors.

HMGA2-NFIB fusion in a pediatric intramuscular lipoma: a novel case of NFIB alteration in a large deep-seated adipocytic tumor

Lipomas are frequently characterized by aberrations of the 12q13 approximately q15 chromosomal region and often by rearrangements of the HMGA2 gene. These rearrangements include the formation of chimeric genes that fuse the 5' region of HMGA2 with a variety of partners, such as LPP (3q28) or NFIB (9p22). We describe here the fourth reported case of lipoma showing a HMGA2-NFIB fusion, and the first one in a child. We found a translocation t(9;12)(p22;q14) in a deep-seated intramuscular lipoma occurring in the buttock of a 5-year-old boy. By fluorescence in situ hybridization and reverse-transcription polymerase chain reaction, we have shown that the translocation t(9;12) resulted in an in-frame fusion of the first four exons of HMGA2 with the last exon of NFIB. Intramuscular lipomas are very rare in childhood. Our results confirm that lipomas containing NFIB rearrangements may be related to peculiar clinicohistologic features, including large size, deep situation, infiltration of surrounding muscles, or precocious occurrence. Both the truncation of HMGA2 and the nature of its fusion partner gene might be relevant in the adipose tissue tumorigenesis.

NFIB rearrangement in superficial, retroperitoneal, and colonic lipomas with aberrations involving chromosome band 9p22

Lipomas are frequently characterized by rearrangements resulting in the fusion of the HMGA2 gene (12q14.3) with a variety of partners. Chromosome band 9p22 rearrangements occur in about 1% of lipomas. We report here the molecular cytogenetic analysis of five cases of lipoma with a 9p22 aberration, including the first cytogenetic analysis of a colonic lipoma. Three out of the five cases showed a rearrangement of NFIB at 9p22.3. The NFIB rearrangement involved a fusion with HMGA2 in two cases. We have identified an in-frame fusion of the first three exons of HMGA2 with exon 6 of MSRB3 (12q14.3) and exons 8 and 9 of NFIB by using 3'RACE-PCR in a case of superficial lipoma. In a case of retroperitoneal lipoma we found a fusion of HMGA2 with NFIB by fluorescence in situ hybridization analysis. The colonic lipoma was characterized by a t(9;16;19)(p22;q21;q13) with a rearrangement of NFIB and no rearrangement of HMGA2. NFIB belongs to the nuclear factor I transcription family. It has been previously shown to be fused with HMGA2 in one case of lipoma and to be a recurrent partner of HMGA2 in pleormorphic adenoma of salivary glands. We here demonstrate that NFIB can also be rearranged independently from HMGA2, indicating a potentially important role in lipoma pathobiology. Our findings suggest that the rearrangement of NFIB might be associated with deep-seated lipomas, such as retroperitoneal or gastro-intestinal lipomas.

The tumor suppressor microRNA let-7 represses the HMGA2 oncogene

HMGA2, a high-mobility group protein, is oncogenic in a variety of tumors, including benign mesenchymal tumors and lung cancers. Knockdown of Dicer in HeLa cells revealed that the HMGA2 gene is transcriptionally active, but its mRNA is destabilized in the cytoplasm through the microRNA (miRNA) pathway. HMGA2 was derepressed upon inhibition of let-7 in cells with high levels of the miRNA. Ectopic expression of let-7 reduced HMGA2 and cell proliferation in a lung cancer cell. The effect of let-7 on HMGA2 was dependent on multiple target sites in the 3' untranslated region (UTR), and the growth-suppressive effect of let-7 on lung cancer cells was rescued by overexpression of the HMGA2 ORF without a 3'UTR. Our results provide a novel example of suppression of an oncogene by a tumor-suppressive miRNA and suggest that some tumors activate the oncogene through chromosomal translocations that eliminate the oncogene's 3'UTR with the let-7 target sites.

Deregulation of HMGA2 in an aggressive angiomyxoma with t(11;12)(q23;q15)

Aggressive angiomyxoma is a soft-tissue neoplasm with a predilection for the pelvic and perineal regions and a tendency to recur locally. Cytogenetic data on this tumor type are limited to five cases, three of which showed rearrangement of chromosomal bands 12q13-15. Molecular investigation of two of the tumors identified the HMGA2 gene as the target of the 12q rearrangements. However, the two previously analyzed tumors were different at the molecular level: in one, the rearrangement of 12q13-15 resulted in a fusion product, whereas, in the second case, the breakpoint was telomeric (3') to the HMGA2, leaving the gene intact although expressed in its entire length. To shed more light on the pathobiology of aggressive angiomyxoma and to investigate the molecular mechanisms behind the involvement of the HMGA2 gene in this tumor type (fusion transcript vs deregulated expression), we investigated, cytogenetically and with molecular techniques, one such tumor which presented a t(11;12)(q23;q15) as the sole karyotypic aberration. FISH analyses demonstrated no structural alteration of HMGA2 at the cytogenetic level; however, expression of the full-length gene was detected molecularly.