Leonardo A. Meza-Zepeda

Modulation of the Osteosarcoma Expression Phenotype by MicroRNAs

Background Osteosarcomas are the most common primary malignant tumors of bone and show multiple and complex genomic aberrations. miRNAs are non-coding RNAs capable of regulating gene expression at the post transcriptional level, and miRNAs and their target genes may represent novel therapeutic targets or biomarkers for osteosarcoma. In order to investigate the involvement of miRNAs in osteosarcoma development, global microarray analyses of a panel of 19 human osteosarcoma cell lines was performed. Principal findings We identified 177 miRNAs that were differentially expressed in osteosarcoma cell lines relative to normal bone. Among these, miR-126/miR-126*, miR-142-3p, miR-150, miR-223, miR-486-5p and members of the miR-1/miR-133a, miR-144/miR-451, miR-195/miR-497 and miR-206/miR-133b clusters were found to be downregulated in osteosarcoma cell lines. All miRNAs in the paralogous clusters miR-17-92, miR-106b-25 and miR-106a-92 were overexpressed. Furthermore, the upregulated miRNAs included miR-9/miR-9*, miR-21*, miR-31/miR-31*, miR-196a/miR-196b, miR-374a and members of the miR-29 and miR-130/301 families. The most interesting inversely correlated miRNA/mRNA pairs in osteosarcoma cell lines included miR-9/TGFBR2 and miR-29/p85α regulatory subunit of PI3K. PTEN mRNA correlated inversely with miR-92a and members of the miR-17 and miR-130/301 families. Expression profiles of selected miRNAs were confirmed in clinical samples. A set of miRNAs, miR-1, miR-18a, miR-18b, miR-19b, miR-31, miR-126, miR-142-3p, miR-133b, miR-144, miR-195, miR-223, miR-451 and miR-497 was identified with an intermediate expression level in osteosarcoma clinical samples compared to osteoblasts and bone, which may reflect the differentiation level of osteosarcoma relative to the undifferentiated osteoblast and fully differentiated normal bone. Significance: This study provides an integrated analysis of miRNA and mRNA in osteosarcoma, and gives new insight into the complex genetic mechanisms of osteosarcoma development and progression.

High‐resolution analysis of genetic stability of human adipose tissue stem cells cultured to senescence

The potential use of human mesenchymal stem cells for therapeutic applications implies large scale in vitro culture, increasing the probability of genetic instability and transformation. We examine here the incidence of unbalanced and balanced chromosome rearrangements in polyclonal and single cell‐derived cultures of human adipose stem cells to senescence. G‐banding karyotyping of the polyclonal cultures shows a normal karyotype. In addition, high‐resolution microarray‐based comparative genomic hybridization analyses relative to uncultured adipose stem cells from the same donors reveal overall genomic stability in long‐term (∼6 months) polyclonal and clonal culture. One adipose stem cell clone displayed minor deletions in gene‐rich telomeric and sub‐telomeric regions on three chromosomes in early passage. This however, was detected only in a sub‐population of cells that was subsequently spontaneously eliminated from the culture. Apparent pericentromeric instabilities are also occasionally detected in specific chromosomes. Our results indicate that clonal chromosomal aberrations may arise transiently in early passage adipose stem cells (ASC) cultures. Nonetheless, incidence of these aberrations seems to be negligible in the majority of long‐term ASC cultures, at least under the culture conditions used here.

Molecular characterization of commonly used cell lines for bone tumor research: A trans-European EuroBoNet effort

Usage of cancer cell lines has repeatedly generated conflicting results provoked by differences among subclones or contamination with mycoplasm or other immortal mammalian cells. To overcome these limitations, we decided within the EuroBoNeT consortium to characterize a common set of cell lines including osteosarcomas (OS), Ewing sarcomas (ES), and chondrosarcomas (CS). DNA fingerprinting was used to guarantee the identity of all of the cell lines and to distinguish subclones of osteosarcoma cell line HOS. Screening for homozygous loss of 38 tumor suppressor genes by MLPA revealed deletion of CDKN2A as the most common event (15/36), strictly associated with absence of the CDKN2A (p16) protein. Ten cell lines showed missense mutations of the TP53 gene while another set of nine cell lines showed mutations resulting in truncation of the TP53 protein. Cells harboring missense mutations expressed high levels of nuclear TP53, while cell lines with nonsense mutations showed weak/absent staining for TP53. TP53wt cell lines usually expressed the protein in 2–10% of the cells. However, seven TP53wt osteosarcomas were negative for both mRNA and protein expression. Our analyses shed light on the correlation between immunohistochemical and genetic data for CDKN2A and TP53, and confirm the importance of these signaling pathways. The characterization of a substantial number of cell lines represents an important step to supply research groups with proven models for further advanced studies on tumor biology and may help to make results from different laboratories more comparable.

Performance comparison of four exome capture systems for deep sequencing

BackgroundRecent developments in deep (next-generation) sequencing technologies are significantly impacting medical research. The global analysis of protein coding regions in genomes of interest by whole exome sequencing is a widely used application. Many technologies for exome capture are commercially available; here we compare the performance of four of them: NimbleGen’s SeqCap EZ v3.0, Agilent’s SureSelect v4.0, Illumina’s TruSeq Exome, and Illumina’s Nextera Exome, all applied to the same human tumor DNA sample.ResultsEach capture technology was evaluated for its coverage of different exome databases, target coverage efficiency, GC bias, sensitivity in single nucleotide variant detection, sensitivity in small indel detection, and technical reproducibility. In general, all technologies performed well; however, our data demonstrated small, but consistent differences between the four capture technologies. Illumina technologies cover more bases in coding and untranslated regions. Furthermore, whereas most of the technologies provide reduced coverage in regions with low or high GC content, the Nextera technology tends to bias towards target regions with high GC content.ConclusionsWe show key differences in performance between the four technologies. Our data should help researchers who are planning exome sequencing to select appropriate exome capture technology for their particular application.

Array Comparative Genomic Hybridization Reveals Distinct DNA Copy Number Differences between Gastrointestinal Stromal Tumors and Leiomyosarcomas

Leiomyosarcomas are spindle cell tumors showing smooth muscle differentiation. Until recently, most gastrointestinal stromal tumors (GIST) were also classified as smooth muscle tumors, but now GISTs are recognized as a separate entity, defined as spindle cell and/or epithelioid tumors localized in the gastrointestinal tract. Using microarray-based comparative genomic hybridization (array CGH), we have created a detailed map of DNA copy number changes for 7 GISTs and 12 leiomyosarcomas. Considerable gains and losses of chromosomal segments were observed in both tumor types. The most frequent aberration observed in GISTs was loss of chromosomes 14 and 22, with minimal recurrent regions in 14q11.2-q32.33 (71% of the tumors) and 22q12.2-q13.31 (100%). In leiomyosarcomas, frequent loss of chromosome 10 and 13q was observed, with minimal recurrent regions in 10q21.3 (75%) and 13q14.2-q14.3 (75%). Recurrent high-level amplification of 17p13.1-p11.2 was detected in leiomyosarcomas. Expression profiling using cDNA microarrays revealed four candidate genes in this region with high expression (AURKB, SREBF1, MFAP4, and FLJ10847). Altered expression of AURKB and SREBF1 has been observed previously in other malignancies. Hierarchical clustering of all samples separated GISTs and leiomyosarcomas into two distinct clusters. Statistical analysis identified six chromosomal regions, 1p36.11-p13.1, 9q21.11-9q34.3, 14q11.2-q23.2, 14q31.3-q32.33, 15q24.3-q26.3, and 22q11.21-q13.31, which were significantly different in copy number between GISTs and leiomyosarcomas. Our results show the potential of using array comparative genomic hybridization to classify histologically similar tumors such as GISTs and leiomyosarcomas.

HMGIC, the gene for an architectural transcription factor, is amplified and rearranged in a subset of human sarcomas

Amplified segments of the long arm of chromosome 12 are frequently observed in human sarcomas. In most cases there are separate amplified regions around the MDM2 and CDK4 genes. Here we show recurrent amplification of a third region encompassing HMGIC, a human architectural transcription factor gene. Reduced amplification frequency of sequences flanking the gene was observed, indicating that inclusion of this third region in the amplicons is also selected for. In three samples only the 5′ part of HMGIC was amplified, suggesting preferential loss of the 3′ part of the gene preceding or during amplification. In several other samples rearrangement of the gene was observed. Expression analysis showed transcripts of aberrant sizes, lacking 3′ sequences, and 3′ RACE of one sample revealed replacement of exons 4 and 5 with ectopic sequences. This truncation of HMGIC resembles that reported for translocations of HMGIC in benign tumors, including lipomas, and it is striking that the gene was frequently amplified or rearranged in well differentiated liposarcomas, the malignant counterpart of lipomas. It seems conceivable that high levels of either full length or truncated hmgic could be relevant for the etiology of these tumors

Deep Sequencing the MicroRNA Transcriptome in Colorectal Cancer

Colorectal cancer (CRC) is one of the leading causes of cancer related deaths and the search for prognostic biomarkers that might improve treatment decisions is warranted. MicroRNAs (miRNAs) are short non-coding RNA molecules involved in regulating gene expression and have been proposed as possible biomarkers in CRC. In order to characterize the miRNA transcriptome, a large cohort including 88 CRC tumors with long-term follow-up was deep sequenced. 523 mature miRNAs were expressed in our cohort, and they exhibited largely uniform expression patterns across tumor samples. Few associations were found between clinical parameters and miRNA expression, among them, low expression of miR-592 and high expression of miR-10b-5p and miR-615-3p were associated with tumors located in the right colon relative to the left colon and rectum. High expression of miR-615-3p was also associated with poorly differentiated tumors. No prognostic biomarker candidates for overall and metastasis-free survival were identified by applying the LASSO method in a Cox proportional hazards model or univariate Cox. Examination of the five most abundantly expressed miRNAs in the cohort (miR-10a-5p, miR-21-5p, miR-22-3p, miR-143-3p and miR-192-5p) revealed that their collective expression represented 54% of the detected miRNA sequences. Pathway analysis of the target genes regulated by the five most highly expressed miRNAs uncovered a significant number of genes involved in the CRC pathway, including APC, TGFβ and PI3K, thus suggesting that these miRNAs are relevant in CRC.

Identification of Osteosarcoma Driver Genes by Integrative Analysis of Copy Number and Gene Expression Data

High‐grade osteosarcoma is a tumor with a complex genomic profile, occurring primarily in adolescents with a second peak at middle age. The extensive genomic alterations obscure the identification of genes driving tumorigenesis during osteosarcoma development. To identify such driver genes, we integrated DNA copy number profiles (Affymetrix SNP 6.0) of 32 diagnostic biopsies with 84 expression profiles (Illumina Human‐6 v2.0) of high‐grade osteosarcoma as compared with its putative progenitor cells, i.e., mesenchymal stem cells (n = 12) or osteoblasts (n = 3). In addition, we performed paired analyses between copy number and expression profiles of a subset of 29 patients for which both DNA and mRNA profiles were available. Integrative analyses were performed in Nexus Copy Number software and statistical language R. Paired analyses were performed on all probes detecting significantly differentially expressed genes in corresponding LIMMA analyses. For both nonpaired and paired analyses, copy number aberration frequency was set to >35%. Nonpaired and paired integrative analyses resulted in 45 and 101 genes, respectively, which were present in both analyses using different control sets. Paired analyses detected >90% of all genes found with the corresponding nonpaired analyses. Remarkably, approximately twice as many genes as found in the corresponding nonpaired analyses were detected. Affected genes were intersected with differentially expressed genes in osteosarcoma cell lines, resulting in 31 new osteosarcoma driver genes. Cell division related genes, such as MCM4 and LATS2, were overrepresented and genomic instability was predictive for metastasis‐free survival, suggesting that deregulation of the cell cycle is a driver of osteosarcomagenesis.

LSAMP, a novel candidate tumor suppressor gene in human osteosarcomas, identified by array comparative genomic hybridization

Osteosarcomas are the most common primary malignant tumor of bone, and almost all conventional osteosarcomas are high‐grade tumors with complex karyotypes. We have examined DNA copy number changes in 36 osteosarcoma tumors and 20 cell lines using microarray‐based comparative genomic hybridization. The most frequent minimal recurrent regions of gain identified in the tumor samples were in 1q21.2‐q21.3 (78% of the samples), 1q21.3‐q22 (78%), and 8q22.1 (72%). Minimal recurrent regions in 10q22.1‐q22.2 (81%), 6q16.1 (67%), 13q14.2 (67%), and 13q21.1 (67%) were most frequently lost. A small region in 3q13.31 (2.1 Mb) containing the gene limbic system‐associated membrane protein (LSAMP) was frequently deleted (56%). LSAMP has previously been reported to be a candidate tumor suppressor gene in other cancer types. The deletion was validated using fluorescence in situ hybridization, and the expression level and promoter methylation status of LSAMP were investigated using quantitative real‐time reverse transcription PCR and methylation‐specific PCR, respectively. LSAMP showed low expression compared to two normal bone samples in 6/15 tumors and 5/9 cell lines with deletion of 3q13.31, and also in 5/14 tumors and 3/11 cell lines with normal copy number or gain. Partial or full methylation of the investigated CpG island was identified in 3/30 tumors and 7/20 cell lines. Statistical analyses revealed that loss of 11p15.4‐p15.3 and low expression of LSAMP (both P = 0.011) were significantly associated with poor survival. Our results show that LSAMP is a novel candidate tumor suppressor gene in osteosarcomas.

Adipocyte differentiation of human bone marrow-derived stromal cells is modulated by MicroRNA-155, MicroRNA-221, and MicroRNA-222

Human mesenchymal stromal cells (hMSCs) are capable of limited self-renewal and multilineage differentiation in vitro. Several studies have demonstrated that microRNAs (miRNAs, miRs), post-transcriptional modifiers of mRNA stability and protein translation, play crucial roles in the regulation of these complex processes. To gain knowledge regarding the role of miRNAs in human adipocyte differentiation, we examined the miRNA expression profile of the immortalized human bone marrow-derived stromal cell line hMSC-Tert20. Such a model system has the advantage of a reproducible and consistent phenotype while maintaining important properties of the primary donor cells, including the potential to differentiate to adipocytes, osteoblasts, and chondrocytes. We identified 12 miRNAs that were differentially expressed during adipogenesis, of which several have been previously shown to play important roles in adipocyte biology. Among these, the expression of miRNA-155, miRNA-221, and miRNA-222 decreased during the adipogenic program of both immortalized and primary hMSCs, suggesting that they act as negative regulators of differentiation. Interestingly, ectopic expression of the miRNAs significantly inhibited adipogenesis and repressed induction of the master regulators PPARγ and CCAAT/enhancer-binding protein alpha. Our study provides the first experimental evidence that miRNA-155, miRNA-221, and miRNA-222 have an important function in human adipocyte differentiation, and that their downregulation is necessary to relieve the repression of genes crucial for this process.