Genome-Wide CRISPR Screen Identifies Regulators of Mitogen-Activated Protein Kinase as Suppressors of Liver Tumors in Mice

BACKGROUND & AIMS

It has been a challenge to identify liver tumor suppressors or oncogenes due to the genetic heterogeneity of these tumors. We performed a genome-wide screen to identify suppressors of liver tumor formation in mice, using CRISPR-mediated genome editing.

METHODS

We performed a genome-wide CRISPR/Cas9-based knockout screen of P53-null mouse embryonic liver progenitor cells that overexpressed MYC. We infected p53-/-;Myc;Cas9 hepatocytes with the mGeCKOa lentiviral library of 67,000 single-guide RNAs (sgRNAs), targeting 20,611 mouse genes, and transplanted the transduced cells subcutaneously into nude mice. Within 1 month, all the mice that received the sgRNA library developed subcutaneous tumors. We performed high-throughput sequencing of tumor DNA and identified sgRNAs increased at least 8-fold compared to the initial cell pool. To validate the top 10 candidate tumor suppressors from this screen, we collected data from patients with hepatocellular carcinoma (HCC) using the Cancer Genome Atlas and COSMIC databases. We used CRISPR to inactivate candidate tumor suppressor genes in p53-/-;Myc;Cas9 cells and transplanted them subcutaneously into nude mice; tumor formation was monitored and tumors were analyzed by histology and immunohistochemistry. Mice with liver-specific disruption of p53 were given hydrodynamic tail-vein injections of plasmids encoding Myc and sgRNA/Cas9 designed to disrupt candidate tumor suppressors; growth of tumors and metastases was monitored. We compared gene expression profiles of liver cells with vs without tumor suppressor gene disrupted by sgRNA/Cas9. Genes found to be up-regulated after tumor suppressor loss were examined in liver cancer cell lines; their expression was knocked down using small hairpin RNAs, and tumor growth was examined in nude mice. Effects of the MEK inhibitors AZD6244, U0126, and trametinib, or the multi-kinase inhibitor sorafenib, were examined in human and mouse HCC cell lines.

RESULTS

We identified 4 candidate liver tumor suppressor genes not previously associated with liver cancer (Nf1, Plxnb1, Flrt2, and B9d1). CRISPR-mediated knockout of Nf1, a negative regulator of RAS, accelerated liver tumor formation in mice. Loss of Nf1 or activation of RAS up-regulated the liver progenitor cell markers HMGA2 and SOX9. RAS pathway inhibitors suppressed the activation of the Hmga2 and Sox9 genes that resulted from loss of Nf1 or oncogenic activation of RAS. Knockdown of HMGA2 delayed formation of xenograft tumors from cells that expressed oncogenic RAS. In human HCCs, low levels of NF1 messenger RNA or high levels of HMGA2 messenger RNA were associated with shorter patient survival time. Liver cancer cells with inactivation of Plxnb1, Flrt2, and B9d1 formed more tumors in mice and had increased levels of mitogen-activated protein kinase phosphorylation.

CONCLUSIONS

Using a CRISPR-based strategy, we identified Nf1, Plxnb1, Flrt2, and B9d1 as suppressors of liver tumor formation. We validated the observation that RAS signaling, via mitogen-activated protein kinase, contributes to formation of liver tumors in mice. We associated decreased levels of NF1 and increased levels of its downstream protein HMGA2 with survival times of patients with HCC. Strategies to inhibit or reduce HMGA2 might be developed to treat patients with liver cancer.

HMGA2 regulates transcription of the Imp2 gene via an intronic regulatory element in cooperation with nuclear factor-kappaB

IMP2 (insulin-like growth factor-II mRNA binding protein 2) is an oncofetal protein that is aberrantly expressed in several types of cancer. We recently identified the Imp2 gene as a target gene of the architectural transcription factor HMGA2 (high mobility group A2) and its tumor-specific truncated form HMGA2Tr. In this study, we investigated the mechanism via which HMGA2 regulates Imp2 gene expression. We show that HMGA2 and HMGA2Tr directly regulate transcription of the Imp2 gene by binding to an AT-rich regulatory region located in the first intron. In reporter experiments, we show that this AT-rich regulatory region mimics the response of the endogenous Imp2 gene to HMGA2 and HMGA2Tr. Furthermore, we show that a consensus nuclear factor-kappaB (NF-kappaB) binding site located immediately adjacent to the AT-rich regulatory region binds NF-kappaB and that NF-kappaB and HMGA2 cooperate to regulate Imp2 gene expression. Finally, we provide evidence that there is a strong and statistically significant correlation between HMGA2 and IMP2 gene expression in human liposarcomas.

HMGA2: a biomarker significantly overexpressed in high-grade ovarian serous carcinoma

Ovarian carcinoma consists of a group of histologically heterogeneous diseases involving distinct tumorigenic pathways. High-grade papillary serous carcinoma of the ovary is commonly associated with p53 mutations. HMGA2, an oncofetal protein, is found to be overexpressed in ovarian cancer. To study the function of HMGA2 in ovarian cancer, it is important to know which subtypes of ovarian cancer are associated with HMGA2 overexpression. In this study, we collected six different types of ovarian cancer and examined HMGA2 expression by immunohistochemistry, along with HMGA1, p53 and Ki-67. We found that HMGA2 overexpression was significantly higher in high-grade papillary serous carcinoma (64%) and carcinosarcoma (60%) than in other types of ovarian cancers (7-23%). HMGA2 overexpression was moderately associated with dominant p53 mutations (R=0.51). In addition, the microRNA in situ analysis revealed that let-7b, the HMGA2-negative regulators, were significantly lost in high-grade serous carcinoma. Our findings suggest that HMGA2 is an important molecular change significantly related to high-grade papillary serous carcinoma and is less common in other histological types of ovarian cancer.

MicroRNA-543 suppresses colorectal cancer growth and metastasis by targeting KRAS, MTA1 and HMGA2

miR-543 has been implicated as having a critical role in the development of breast cancer, endometrial cancer and hepatocellular carcinoma. However, the exact clinical significance and biological functions of miR-543 in colorectal cancer (CRC) remain unclear. Here, we found that miR-543 expression significantly downregulated in tumors from patients with CRC, APCMin mice and a mouse model of colitis-associated colon cancer. miR-543 level was inversely correlated with the metastatic status of patients with CRC and the metastatic potential of CRC cell lines. Moreover, ectopic expression of miR-543 inhibited the proliferation and metastasis of CRC cells in vitro and in vivo by targeting KRAS, MTA1 and HMGA2. Conversely, miR-543 knockdown promoted the proliferation, migration and invasion of CRC cells in vitro and augmented tumor growth and metastasis in vivo. Furthermore, we found that miR-543 expression was negatively correlated with the levels of KRAS, MTA1 and HMGA2 in clinical samples. Collectively, these data show that miR-543 inhibits the proliferation and metastasis of CRC cells by targeting KRAS, MTA1 and HMGA2. Our study highlights a pivotal role for miR-543 as a suppressor in the regulation of CRC growth and metastasis and suggests that miR-543 may serve as a novel diagnostic and prognostic biomarker for CRC metastasis.

Fusion, disruption, and expression of HMGA2 in bone and soft tissue chondromas

Soft tissue and skeletal chondromas are rare entities, and only 21 cases with abnormal karyotypes have been reported. A survey of these, and 10 new cases reported herein, showed that the 12q13-15 segment is nonrandomly involved in structural rearrangements in chondromas. The HMGA2 (HMGI-C) locus in 12q15 is frequently rearranged in other benign mesenchymal tumors, and this study aimed at characterizing the expression of HMGA2 in chondromatous tumors. The material consisted of 8 soft tissue and 6 skeletal chondromas, as well as of 14 skeletal chondrosarcomas. All cases had been cytogenetically analyzed. Expression of HMGA2 could be assessed by RT-PCR in 8 chondromas and 13 chondrosarcomas. HMGA2 was expressed in 4 of six soft tissue chondromas, all displaying 12q-rearrangements at cytogenetic analysis. A truncated transcript (exons 1-3), but not a full-length (exons 1-5) transcript, was detected in three of them, suggesting activation through an intragenic rearrangement. One soft tissue chondroma had a t(3;12)(q27;q15), and the RT-PCR analysis revealed an HMGA2-LPP fusion transcript, composed of HMGA2 exons 1-3 and LPP exons 9-11. An identical fusion transcript previously has been identified in lipoma and pulmonary chondroid hamartoma. In the fourth soft tissue chondroma, a full-length transcript was detected, indicating expression of at least one intact allele. Both skeletal chondromas expressed HMGA2. In one of them, a full-length transcript was detected, even though 12q was cytogenetically unaffected. A truncated or full-length transcript was found in 8 of 13 chondrosarcomas, 4 of which displayed 12q rearrangements. Possibly, cryptic rearrangements were present among the many complex marker chromosomes in the remaining 4 cases.

Hyaline vascular Castleman's disease with HMGIC rearrangement in follicular dendritic cells: molecular evidence of mesenchymal tumorigenesis

Chromosomal aberrations involving chromosome segment 12q13-15 are a common finding in a variety of benign mesenchymal tumors. The target gene encodes for HMGIC, a member of the high mobility group protein family. These proteins act as architectural transcription factors. HMGIC plays a role as a common genetic denominator in benign mesenchymal tumorigenesis. We report a case of hyaline vascular Castleman's disease with intragenic HMGIC rearrangement, due to a clonal cytogenetic aberration involving the long arm of chromosome 12 [46,XX, add(1)(q21),der(6)t(6;12) (q23;q15),add(7)(p22), -9,inv(9)(p11q13),del(12)(q15),+mar] obtained after short-term primary cultures. A combined immunocytologic-cytogenetic approach enabled us to demonstrate the exclusive presence of HMGIC rearrangement in anti-CD21 reactive follicular dendric cells. This finding confirms that a clonal proliferation of follicular dendritic cells occurs in the hyaline vascular variant of Castleman's disease. It also provides a possible molecular pathway explaining stromal overgrowths and stromal neoplasms developing from this disorder.

Mir-23b and miR-130b expression is downregulated in pituitary adenomas

MicroRNA (miRNA) deregulation plays a critical role in tumorigenesis. miR-23b and miR-130b are induced by thyrotropin in thyroid cells in a cAMP-dependent manner. The aim of our work has been to investigate the possible role of miR-23b and miR-130b in pituitary tumorigenesis. We have analyzed their expression in a panel of pituitary adenomas (PAs) including GH and NFPA adenomas. We report that miR-23b and miR-130b are drastically reduced in GH, gonadotroph and NFPA adenomas in comparison with normal pituitary gland. Interestingly, the overexpression of miR-23b and miR-130b inhibits cell proliferation arresting the cells in the G1 and G2 phase of the cell cycle, respectively. Moreover, we demonstrate that miR-23b and miR-130b target HMGA2 and cyclin A2 (CCNA2) genes, respectively. Finally, downregulation of miR-23b and miR-130b expression is associated with increased levels of their respective targets in human PAs. These findings suggest that miR-23b and miR-130b downregulation may contribute to pituitary tumorigenesis.

Misexpression of full-length HMGA2 induces benign mesenchymal tumors in mice

The high-mobility group AT-hook 2 (HMGA2) protein is a member of the high-mobility group family of the DNA-binding architectural factors and participates in the conformational regulation of active chromatin on its specific downstream target genes. HMGA2 is expressed in the undifferentiated mesenchyme and is undetectable in their differentiated counterparts, suggesting its functional importance in mesenchymal cellular proliferation and differentiation. Interestingly, it is a frequent target of chromosomal translocations in several types of human benign differentiated mesenchymal tumors, including lipomas, fibroadenomas of the breast, salivary gland adenomas, and endometrial polyps. The translocations lead to a variety of HMGA2 transcripts, which range from wild-type, truncated, and fusion mRNA species. However, it is not clear whether alteration of the HMGA2 transcript is required for its tumorigenic potential. To determine whether misexpression of HMGA2 in differentiated mesenchymal cells is sufficient to cause tumorigenesis, we produced transgenic mice that misexpressed full-length or truncated human HMGA2 transcript under the control of the differentiated mesenchymal cell (adipocyte)-specific promoter of the adipocyte P2 (Fabp4) gene. Expression of the full-length HMGA2 transgene was observed in a number of tissues, which produced neoplastic phenotype, including fibroadenomas of the breast and salivary gland adenomas. Furthermore, transgenic misexpression of the truncated version of HMGA2, containing only the three DNA-binding domains, produced similar phenotypes. These results show that misexpression of HMGA2 in a differentiated mesenchymal cell is sufficient to cause mesenchymal tumorigenesis and is independent of the nature of the HMGA2 transcript that results from chromosomal translocations observed in humans.

Dying tumor cell-derived exosomal miR-194-5p potentiates survival and repopulation of tumor repopulating cells upon radiotherapy in pancreatic cancer

BACKGROUND

Tumor repopulation is a major cause of radiotherapy failure. Previous investigations highlighted that dying tumor cells played vital roles in tumor repopulation through promoting proliferation of the residual tumor repopulating cells (TRCs). However, TRCs also suffer DNA damage after radiotherapy, and might undergo mitotic catastrophe under the stimulation of proliferative factors released by dying cells. Hence, we intend to find out how these paradoxical biological processes coordinated to potentiate tumor repopulation after radiotherapy.

METHODS

Tumor repopulation models in vitro and in vivo were used for evaluating the therapy response and dissecting underlying mechanisms. RNA-seq was performed to find out the signaling changes and identify the significantly changed miRNAs. qPCR, western blot, IHC, FACS, colony formation assay, etc. were carried out to analyze the molecules and cells.

RESULTS

Exosomes derived from dying tumor cells induced G1/S arrest and promoted DNA damage response to potentiate survival of TRCs through delivering miR-194-5p, which further modulated E2F3 expression. Moreover, exosomal miR-194-5p alleviated the harmful effects of oncogenic HMGA2 under radiotherapy. After a latent time, dying tumor cells further released a large amount of PGE2 to boost proliferation of the recovered TRCs, and orchestrated the repopulation cascades. Of note, low-dose aspirin was found to suppress pancreatic cancer repopulation upon radiation via inhibiting secretion of exosomes and PGE2.

CONCLUSION

Exosomal miR-194-5p enhanced DNA damage response in TRCs to potentiate tumor repopulation. Combined use of aspirin and radiotherapy might benefit pancreatic cancer patients.

Let-7 Represses Carcinogenesis and a Stem Cell Phenotype in the Intestine via Regulation of Hmga2

Let-7 miRNAs comprise one of the largest and most highly expressed family of miRNAs among vertebrates, and is critical for promoting differentiation, regulating metabolism, inhibiting cellular proliferation, and repressing carcinogenesis in a variety of tissues. The large size of the Let-7 family of miRNAs has complicated the development of mutant animal models. Here we describe the comprehensive repression of all Let-7 miRNAs in the intestinal epithelium via low-level tissue-specific expression of the Lin28b RNA-binding protein and a conditional knockout of the MirLet7c-2/Mirlet7b locus. This ablation of Let-7 triggers the development of intestinal adenocarcinomas concomitant with reduced survival. Analysis of both mouse and human intestinal cancer specimens reveals that stem cell markers were significantly associated with loss of Let-7 miRNA expression, and that a number of Let-7 targets were elevated, including Hmga1 and Hmga2. Functional studies in 3-D enteroids revealed that Hmga2 is necessary and sufficient to mediate many characteristics of Let-7 depletion, namely accelerating cell cycle progression and enhancing a stem cell phenotype. In addition, inactivation of a single Hmga2 allele in the mouse intestine epithelium significantly represses tumorigenesis driven by Lin28b. In aggregate, we conclude that Let-7 depletion drives a stem cell phenotype and the development of intestinal cancer, primarily via Hmga2.

Cancer develops following multiple genetic mutations (i.e. in tumor suppressors and oncogenes), and mutations that cooperate or synergize are often advantageous to cancer cell growth. To study how multiple genes might cooperate, it is usually informative to generate candidate mutations in cells or in mice. Large gene families, such as the Let-7 family, are difficult to silence or mutate because of the large amount of redundancy that exists between similar copies of the same gene; the mutation of one will often be masked or compensated by the continued function of others. In the mouse intestine we have achieved comprehensive depletion of all Let-7 miRNAs in this large multi-genic family through use of an inhibitory protein, called LIN28B, that specifically represses Let-7, and genetic inactivation of another gene cluster called MirLet7c-2/Mirlet7b. Mice with this comprehensive depletion of Let-7 develop intestinal cancers that resemble human colon cancers. Our further analysis identified another gene, HMGA2, downstream of this pathway that is critical to this outcome.

Assessment of the clinical and molecular impact of different cytogenetic subgroups in a series of 272 lipomas with abnormal karyotype

Conventional lipomas harbor karyotypic changes that could be subdivided into four, usually mutually exclusive, categories: rearrangement, in particular through translocations, of chromosome bands 12q13-15, resulting in deregulation of the HMGA2 gene, loss of material from or rearrangement of chromosome 13, supernumerary ring or giant marker chromosomes, and aberrations of chromosome band 6p21. In the present study, 272 conventional lipomas, two-thirds of them deep-seated, with acquired clonal chromosome changes were assessed with regard to karyotypic and clinical features. A nonrandom distribution of breakpoints and imbalances could be confirmed, with 83% of the cases harboring one or more of the previously known cytogenetic hallmarks. Correlation with clinical features revealed that lipomas with rings/giant markers were larger, occurred in older patients, were more often deep-seated, and seemed to have an increased tendency to recur locally, compared with tumors with other chromosome aberrations. The possible involvement of the HMGA2 gene in cases that did not show any of the characteristic cytogenetic changes was further evaluated by locus-specific metaphase fluorescence in situ hybridization (FISH) and RT-PCR, revealing infrequent cryptic disruption of the gene but abundant expression of full length or truncated transcripts. By FISH, we could also show that breakpoints in bands 10q22-23 do not affect the MYST4 gene, whereas breakpoints in 6p21 or 8q11-12 occasionally target the HMGA1 or PLAG1 genes, respectively, also in conventional lipomas.

Let-7a is a direct EWS-FLI-1 target implicated in Ewing's sarcoma development

Ewing's sarcoma family tumors (ESFT) are the second most common bone malignancy in children and young adults, characterized by unique chromosomal translocations that in 85% of cases lead to expression of the EWS-FLI-1 fusion protein. EWS-FLI-1 functions as an aberrant transcription factor that can both induce and suppress members of its target gene repertoire. We have recently demonstrated that EWS-FLI-1 can alter microRNA (miRNA) expression and that miRNA145 is a direct EWS-FLI-1 target whose suppression is implicated in ESFT development. Here, we use miRNA arrays to compare the global miRNA expression profile of human mesenchymal stem cells (MSC) and ESFT cell lines, and show that ESFT display a distinct miRNA signature that includes induction of the oncogenic miRNA 17–92 cluster and repression of the tumor suppressor let-7 family. We demonstrate that direct repression of let-7a by EWS-FLI-1 participates in the tumorigenic potential of ESFT cells in vivo. The mechanism whereby let-7a expression regulates ESFT growth is shown to be mediated by its target gene HMGA2, as let-7a overexpression and HMGA2 repression both block ESFT cell tumorigenicity. Consistent with these observations, systemic delivery of synthetic let-7a into ESFT-bearing mice restored its expression in tumor cells, decreased HMGA2 expression levels and resulted in ESFT growth inhibition in vivo. Our observations provide evidence that deregulation of let-7a target gene expression participates in ESFT development and identify let-7a as promising new therapeutic target for one of the most aggressive pediatric malignancies.

HMGA2 expression in uterine leiomyomata and myometrium: quantitative analysis and tissue culture studies

The high mobility group gene, HMGA2, is frequently expressed in uterine leiomyomata (UL) with chromosomal rearrangements of 12q15. In contrast, HMGA2 expression has not been detected in karyotypically normal UL or in myometrium, but has been detected in these tissues after culture. To characterize further the expression pattern of HMGA2, we assessed HMGA2 expression by RT-PCR followed by Southern blot hybridization, and by real-time PCR in three tissue panels: (1) primary myometrial cultures, (2) uncultured tissue from 15 karyotypically normal samples consisting of eleven 46,XX UL and four matched myometrial specimens, and (3) uncultured tissue from ten UL with 12q15 rearrangements and three matched myometrial specimens. HMGA2 expression was detected in all samples from the three panels. The level of HMGA2 expression in karyotypically normal UL was similar to the level of expression in myometrium; however, it was significantly less than the level measured in UL with 12q15 rearrangements. This expression analysis by use of detection methods of different sensitivities underscores the importance of studies of HMGA2 expression in uncultured tissues and of careful interpretation of results from experiments on cultured cells. Moreover, detection of HMGA2 expression in myometrium and in UL without 12q15 rearrangements, tissues previously thought not to express HMGA2, suggests that HMGA2 expression is required in normal adult myometrial physiology.

Disruption and aberrant expression of HMGA2 as a consequence of diverse chromosomal translocations in myeloid malignancies

Chromosomal translocations that target HMGA2 at chromosome band 12q14 are seen in a variety of malignancies, notably lipoma, pleomorphic salivary adenoma and uterine leiomyoma. Although some HMGA2 fusion genes have been reported, several lines of evidence suggest that the critical pathogenic event is the expression of truncated HMGA2 isoforms. We report here the involvement of HMGA2 in six patients with myeloid neoplasia, dysplastic features and translocations or an inversion involving chromosome bands 12q13-15 and either 7p12, 8q22, 11q23, 12p11, 14q31 or 20q11. Breaks within or very close to HMGA2 were found in all six cases by molecular cytogenetic analysis, leading to overexpression of this gene as assessed by RT-PCR. Truncated transcripts consisting of HMGA2 exons 1-2 or exons 1-3 spliced to intron-derived sequences were identified in two patients, but were not seen in controls. These findings suggest that abnormalities of HMGA2 play an important and previously unsuspected role in myelodysplasia.

Pancreatic circulating tumor cell profiling identifies LIN28B as a metastasis driver and drug target

Pancreatic ductal adenocarcinoma (PDAC) lethality is due to metastatic dissemination. Characterization of rare, heterogeneous circulating tumor cells (CTCs) can provide insight into metastasis and guide development of novel therapies. Using the CTC-iChip to purify CTCs from PDAC patients for RNA-seq characterization, we identify three major correlated gene sets, with stemness genes LIN28B/KLF4, WNT5A, and LGALS3 enriched in each correlated gene set; only LIN28B CTC expression was prognostic. CRISPR knockout of LIN28B-an oncofetal RNA-binding protein exerting diverse effects via negative regulation of let-7 miRNAs and other RNA targets-in cell and animal models confers a less aggressive/metastatic phenotype. This correlates with de-repression of let-7 miRNAs and is mimicked by silencing of downstream let-7 target HMGA2 or chemical inhibition of LIN28B/let-7 binding. Molecular characterization of CTCs provides a unique opportunity to correlated gene set metastatic profiles, identify drivers of dissemination, and develop therapies targeting the "seeds" of metastasis.

DNA architectural factor and proto-oncogene HMGA2 regulates key developmental genes in pluripotent human embryonic stem cells

The high-mobility group (HMG) protein A2 has been studied mostly in the mouse where its function seems critical for embryonic cell growth and adipogenesis, leading to a pygmy phenotype with greatly reduced fat tissue in homozygous knock out mice. We showed recently that among the major HMG proteins, HMGA2 is highly expressed in two human embryonic stem (hES) cell lines. Here, we employed siRNA technology in combination with quantitative reverse transcriptase polymerase chain reaction, stem cell-specific microarray analyses, and cell proliferation assays in order to probe into HMGA2's role(s) in pluripotent hES cells. Our results establish HMGA2 as a regulator of human genes linked to mesenchymal cell differentiation, adipogenesis, and hES cell growth.

Differential regulation of the insulin-like growth factor II mRNA-binding protein genes by architectural transcription factor HMGA2

The developmentally regulated architectural transcription factor, high mobility group A2 (HMGA2), is involved in growth regulation and plays an important role in embryogenesis and tumorigenesis. Little is known, however, about its downstream targets. We performed a search for genes of which expression is strongly altered during embryonic development in two HMGA2-deficient mouse strains, which display a pygmy-phenotype, as compared to wild-type mice. We found that the insulin-like growth factor II mRNA-binding protein 2 gene (IMP2), but not its family members IMP1 and IMP3, was robustly downregulated in mutant E12.5 embryos. Furthermore, we show that wild-type HMGA2 and its tumor-specific truncated form have opposite effects on IMP2 expression. Our results clearly indicate that HMGA2 differentially regulates expression of IMP family members during embryogenesis.

HMGA2: A pituitary tumour subtype-specific oncogene?

The high mobility group AT-hook (HMGA) proteins, a family of DNA architectural factors, are highly expressed during embryogenesis and play a crucial role in several different biological processes, as well as in tumorigenesis of a wide range of tissues, including pituitary. Indeed, HMGA2 has been found rearranged and amplified in human prolactinomas, and transgenic mice overexpressing either Hmga1 or Hmga2 develop pituitary adenomas secreting prolactin and growth hormone. Here, we overview HMGA proteins in human tumours, focusing on pituitary adenomas and the mechanisms by which the HMGA proteins are involved in their onset and development. Different HMGA-dependent potential drives of pituitary oncogenesis are discussed as future research directions in the field.

Downregulation of HMGA2 by the pan-deacetylase inhibitor panobinostat is dependent on hsa-let-7b expression in liver cancer cell lines

Inhibitors of protein deacetylases represent a novel therapeutic option for cancer diseases due to their effects on transcriptional regulation by interfering with histones acetylation and on several other cellular pathways. Recently, their ability to modulate several transcription factors and, interestingly, also co-factors, which actively participate in formation and modulation of transcription complexes was shown. We here investigate whether HMGA2 (High Mobility Group AT-2 hook), a nuclear non-histone transcriptional co-factor with known oncogenic properties, can be influenced by the novel pan-deacetylase inhibitor panobinostat (LBH589) in human hepatocellular carcinoma models. Panobinostat strongly downregulated HMGA2 in HepG2 and Hep3B cells; this effect was mediated by transcriptional upregulation and promotion of the maturation of the tumorsuppressor miRNA hsa-let-7b, which could inhibit HMGA2 expression via RNA interference pathways. siRNA knockdown of HMGA2 or transfection of hsa-let-7b mimicking oligonucleotides confirmed the role of HMGA2 in regulating cell proliferation and apoptosis in liver cancer cell lines. Co-incubation with panobinostat showed an additive effect on inhibition of cell proliferation using an impedance-based real-time cell analyzer. Treatment of HepG2 xenografts with panobinostat also led to a downregulation of HMGA2 in vivo. These findings show that pan-deacetylase inhibitors also modulate other signaling pathways and networks than histone modifications to influence cell fate.

The genetics of uterine leiomyomata: what clinicians need to know

The genetics of many complex diseases, including hypertension, diabetes, and asthma, are receiving intense investigation and beginning to have therapeutic relevance. Family medical history can be a critical source of information for providing optimal patient care. For gynecologists, knowledge of cancer susceptibility genes such as BRCA1 and BRCA2 and the genetic syndrome hereditary nonpolyposis colorectal cancer (Lynch syndrome II) affects how patients are screened for ovarian and endometrial cancers. Similarly, identification of mutations in the fumarate hydratase (FH) gene that lead to a syndrome called hereditary leiomyomatosis and renal cell carcinoma (HLRCC) will impact screening and treatment of women with uterine leiomyomas. Hereditary leiomyomatosis and renal cell carcinoma syndrome is particularly relevant to clinicians and patients because of the resulting increased risk of malignant disease for both the affected woman and her family. The goals of this article are to summarize the evolving genetic information concerning uterine leiomyomas, including hereditary leiomyomatosis and renal cell carcinoma syndrome, and to discuss the clinical importance of these findings. The current role of family medical history and future implications of genes relevant to leiomyoma biology will be reviewed.

Translocation, deletion/amplification, and expression of HMGIC and MDM2 in a carcinoma ex pleomorphic adenoma

Carcinoma ex pleomorphic adenoma (CexPA) is a carcinoma developing within a pre-existing benign pleomorphic adenoma (PA). Here we describe the identification and characterization of a series of genetic events leading to translocation, deletion/amplification, and overexpression of the HMGIC and MDM2 genes in a CexPA at an early stage of development. The tumor had a pseudodiploid stemline karyotype with a del(5)(q22-23q32-33) and a t(10;12)(p15;q14-15). In addition, there were several sidelines with double minute chromosomes (dmin) or homogeneously staining regions (hsr). Fluorescence in situ hybridization (FISH) mapping revealed that the 12q14-15 breakpoint was located centromeric to HMGIC and that the entire gene was juxtaposed to the der(10) chromosome. Detailed analysis of cells with dmin and hsr revealed that HMGIC and MDM2 were deleted from the der(10) and that the dmin and hsr were strongly positive for both genes. Southern blot analysis confirmed that both HMGIC and MDM2 were amplified and that no gross rearrangements of the genes had occurred. Immunostaining revealed that the HMGIC protein was highly overexpressed particularly in the large polymorphic cells within the carcinomatous part of the tumor. These findings suggest that amplification and overexpression of HMGIC and possibly MDM2 might be important genetic events that may contribute to malignant transformation of benign PA.

miR-125b-5p functions as a tumor suppressor gene partially by regulating HMGA2 in esophageal squamous cell carcinoma

MicroRNAs (miRNAs) play important roles in the progression of human cancer including esophageal squamous cell carcinoma (ESCC). Although previous reports showed that miR-125b-5p was down-regulated in ESCC, the roles and mechanisms of loss of function of miR-125b-5p in ESCC were still unknown. Using microRNA microarray and GEO datasets, we found and confirmed that miR-125b-5p was down-regulated in ESCC tissues. In-vitro assays showed that ectopic miR-125b-5p expression repressed cell proliferation, migration and invasion, and induced cell senescence. We also found that miR-125b-5p reduced the expressions of cell cycle regulatory genes including CCNA2, CCND1 and CCNE1, and regulated the markers of epithelial to mesenchymal transition (EMT) including E-cadherin, N-cadherin and EMT associated transcription factor Slug, and also decreased the MMPs including MMP2, MMP7 and MMP13. Furthermore, the candidate target gene HMGA2 was negatively regulated by miR-125b-5p both in mRNA and protein levels. Importantly, knockdown of HMGA2 partially phenocopied the effects of miR-125b-5p overexpression on cell cycle regulators and EMT markers. In conclusion, our results suggested that overexpression of miR-125b-5p inhibited cell proliferation, migration and invasion partially by down-regulating HMGA2 in ESCC.

High-level expression of DNA architectural factor HMGA2 and its association with nucleosomes in human embryonic stem cells

The state of chromatin in human embryonic stem (hES) cells is a key factor determining stem cell identity. The non-histone chromatin-associated factor HMGA2 has been studied mostly in the mouse where its function seems critical for embryonic cell growth and adipocytic cell differentiation. Here we show that HMGA2 is highly expressed in two undifferentiated human embryonic stem cell lines at a level of at least 10(5) copies per individual stem cell. Interestingly, expression is further upregulated by a factor of three at day 7 of embryoid body formation, before it quickly drops to or below the level found in undifferentiated cells. We also show that HMGA2 is stably associated with inter- and metaphase hES cell chromatin, and that up to 12 HMGA2 protomers stably associate in vitro with a single nucleosome core particle of known atomic structure. Our data lend support to the possibility that HMGA2 interacts with nucleosomes in a way that imposes a global effect on the state of ES cell chromatin, which may contribute to the establishment of both ES cell identity and the initiation of specific differentiation programs.

The WNT10B Network Is Associated with Survival and Metastases in Chemoresistant Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) commonly develops resistance to chemotherapy, yet markers predictive of chemoresistance in this disease are lacking. Here, we define WNT10B-dependent biomarkers for β-CATENIN/HMGA2/EZH2 signaling predictive of reduced relapse-free survival. Concordant expression of HMGA2 and EZH2 proteins is observed in MMTV-Wnt10bLacZ transgenic mice during metastasis, and Hmga2 haploinsufficiency decreased EZH2 protein expression, repressing lung metastasis. A novel autoregulatory loop interdependent on HMGA2 and EZH2 expression is essential for β-CATENIN/TCF-4/LEF-1 transcription. Mechanistically, both HMGA2 and EZH2 displaced Groucho/TLE1 from TCF-4 and served as gatekeepers for K49 acetylation on β-CATENIN, which is essential for transcription. In addition, we discovered that HMGA2-EZH2 interacts with the PRC2 complex. Absence of HMGA2 or EZH2 expression or chemical inhibition of Wnt signaling in a chemoresistant patient-derived xenograft (PDX) model of TNBC abolished visceral metastasis, repressing AXIN2, MYC, EZH2, and HMGA2 expression in vivo. Combinatorial therapy of a WNT inhibitor with doxorubicin synergistically activated apoptosis in vitro, resensitized PDX-derived cells to doxorubicin, and repressed lung metastasis in vivo. We propose that targeting the WNT10B biomarker network will provide improved outcomes for TNBC. SIGNIFICANCE: These findings reveal targeting the WNT signaling pathway as a potential therapeutic strategy in triple-negative breast cancer.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/5/982/F1.large.jpg.

Osteopoikilosis, short stature and mental retardation as key features of a new microdeletion syndrome on 12q14

This report presents the detection of a heterozygous deletion at chromosome 12q14 in three unrelated patients with a similar phenotype consisting of mild mental retardation, failure to thrive in infancy, proportionate short stature and osteopoikilosis as the most characteristic features. In each case, this interstitial deletion was found using molecular karyotyping. The deletion occurred as a de novo event and varied between 3.44 and 6 megabases (Mb) in size with a 3.44 Mb common deleted region. The deleted interval was not flanked by low-copy repeats or segmental duplications. It contains 13 RefSeq genes, including LEMD3, which was previously shown to be the causal gene for osteopoikilosis. The observation of osteopoikilosis lesions should facilitate recognition of this new microdeletion syndrome among children with failure to thrive, short stature and learning disabilities.