Project description:Acquisition of independence from anchorage to the extracellular matrix is a critical event for onset and progression of solid cancers. To identify and characterize new genes conferring anchorage independence, we transduced MCF10A human normal breast cells with a retroviral cDNA expression library and selected them by growth in suspension. Microarray analysis targeted on library-derived transcripts revealed robust and reproducible enrichment, after selection, of cDNAs encoding the scaffolding adaptor Gab2. Gab2 was confirmed to strongly promote anchorage-independent growth when overexpressed. Interestingly, downregulation by RNAi of endogenous Gab2 in neoplastic cells did not affect their adherent growth, but abrogated their growth in soft agar. Gab2-driven anchorage independence was found to specifically involve activation of the Src-Stat3 signaling axis. A transcriptional “signature” of 205 genes was obtained from GAB2-transduced, anchorage-independent MCF10A cells, and found to contain two main functional modules, respectively controlling proliferation and cell adhesion/migration/invasion. Extensive validation on breast cancer datasets showed that the Gab2-signature provides a robust prognostic classifier for breast cancer metastatic relapse, largely independent from existing clinical and genomic indicators and from estrogen receptor status. This work highlights a pivotal role for GAB2 and its transcriptional targets in anchorage-independent growth and breast cancer metastatic progression.
Project description:Background Systematic search for genes whose gain-of-function by exogenous expression confers an advantage in cell-based selective screenings is a powerful method for unbiased functional exploration of the genome, and has the potential to disclose new targets for cancer therapy. A major limit of this approach resides in the labor-intensive cloning of resistant cells, identification of the integrated genes and validation of their ability to confer a selective advantage. Moreover, the selection has to be drastic and genes conferring a limited advantage are typically missed. Results We developed a new functional screening strategy based on transduction of mammalian cells of a given species with an expression library from another species, followed by one-shot quantitative tracing with DNA microarrays of all library-derived transcripts before and after selection. In this way, exogenous transcripts enriched after selection, and therefore likely to confer resistance, are readily detected. We transduced a retroviral cDNA expression library from mouse testis into human and canine cells, and optimized the use of commercial murine gene expression arrays for species-specific detection of library-derived transcripts. We then conducted a functional screening by growing library-transduced canine MDCK cells in suspension, to enrich for cDNAs conferring anchorage independence. Notably, these cells show partial resistance to loss of anchorage, and the selection can be of limited stringency, compromising approaches based on clonal selection or anyway requiring high stringency. Microarray analysis revealed reproducible enrichment after three weeks of growth on polyhema for seven genes, among which the Hras proto-oncogene and Sox5. When individually transduced into MDCK cells, Sox5 specifically promoted anchorage-independent growth, thereby confirming the validity and specificity of the approach. Conclusions The procedure described here brings substantial advantages to the field of expression cloning, being faster, more systematic and more sensitive. Indeed, this strategy allowed identification and validation of genes promoting anchorage-independent growth of epithelial cells under selection conditions not amenable to conventional expression cloning. Keywords: Xenoarray - a barcode-type microarray-based functional screening.
Project description:Cultured human embryonic stem (hES) cells can acquire genetic and epigenetic changes that make them vulnerable to transformation. As hES cells with cancer-cell characteristics share properties with normal hES cells, such as self-renewal, teratoma formation and the expression of pluripotency markers, they may be misconstrued as superior hES cells with enhanced âstemnessâ. We characterize two variant hES cell lines (v-hESC-1 and v-hESC-2) that express pluripotency markers at high levels and do not harbor chromosomal abnormalities by standard cytogenetic measures. We show that the two lines possess some features of neoplastic progression, including a high proliferative capacity, growth-factor independence, a 9- to 20-fold increase in frequency of tumor initiating cells, niche independence and aberrant lineage specification, although they are not malignant. Array comparative genomic hybridization revealed an amplification at 20q11.1-11.2 in v-hESC-1 and a deletion at 5q34a-5q34b;5q3 and a mosaic gain of chromosome 12 in v-hESC-2. These results emphasize the need for functional characterization to distinguish partially transformed and normal hES cells. Custom oligonucleotide array gene expression analysis was performed on total RNA from low passage normal and variant human embryonic stem cell (hESC) lines, all cultured in our laboratory under the same conditions. Furthermore, array-based comparative genomic hybridization was also performed on the normal and variant hESC lines. v-hESC-1 and v-hESC-2 represent two independent lines that display neoplastic characteristics with distinctive copy number alterations. v-hESC-1_A2B5 represents neural precursor cultures differentiated from variant hES cells. GSM349016-GSM349022: Gene expression analysis GSM351500-GSM351511: aCGH analysis
Project description:Cervical cancer and a subset of anogenital and head-and-neck carcinomas are caused by persistent infection with high-risk types of the human papillomavirus (hrHPV). Early stages of hrHPV-induced carcinogenesis can be faithfully mimicked in vitro. A major hallmark of hrHPV-transformed cells is their ability to grow anchorage independently, an oncogenic trait known to depend on inactivation of tumour suppressor genes. This study used an in vitro model of hrHPV-induced transformation to delineate in a longitudinal manner to what extent DNA methylation-mediated silencing of tumour suppressive microRNAs (miRNAs) contributed to hrHPV-induced anchorage independence. Genome-wide miRNA expression profiles were yielded from anchorage dependent (n=11) and independent passages (n=19) of 4 hrHPV-immortalised keratinocyte cell lines with and without demethylating treatment (DAC). Unsupervised clustering analysis showed that overall miRNA expression patterns discriminated between anchorage dependent and independent cells. Ten miRNA genes potentially silenced by methylation were selected and validated by bisulfite sequencing and methylation-specific PCR. Hsa-mir-129-2, -137, -935, -3663, -3665, and -4281 showed increased methylation in both HPV-transformed keratinocytes and cervical cancer cell lines compared to primary keratinocytes. Mature miRNAs derived from hsa-mir-129-2, -137, -3663, and -3665 decreased anchorage independence in cervical cancer cell lines. Finally, significantly increased methylation of hsa-mir-129-2, -935, -3663, -3665, and -4281 was observed in cervical (pre)cancerous lesions, underlining the clinical relevance of our findings. In conclusion, methylation-mediated silencing of tumour suppressive miRNAs contributes to the acquisition of anchorage independence, supporting the importance of miRNAs during early stages of carcinogenesis and underlining their potential as both disease markers and therapeutic targets.
Project description:Cervical cancer and a subset of anogenital and head-and-neck carcinomas are caused by persistent infection with high-risk types of the human papillomavirus (hrHPV). Early stages of hrHPV-induced carcinogenesis can be faithfully mimicked in vitro. A major hallmark of hrHPV-transformed cells is their ability to grow anchorage independently, an oncogenic trait known to depend on inactivation of tumour suppressor genes. This study used an in vitro model of hrHPV-induced transformation to delineate in a longitudinal manner to what extent DNA methylation-mediated silencing of tumour suppressive microRNAs (miRNAs) contributed to hrHPV-induced anchorage independence. Genome-wide miRNA expression profiles were yielded from anchorage dependent (n=11) and independent passages (n=19) of 4 hrHPV-immortalised keratinocyte cell lines with and without demethylating treatment (DAC). Unsupervised clustering analysis showed that overall miRNA expression patterns discriminated between anchorage dependent and independent cells. Ten miRNA genes potentially silenced by methylation were selected and validated by bisulfite sequencing and methylation-specific PCR. Hsa-mir-129-2, -137, -935, -3663, -3665, and -4281 showed increased methylation in both HPV-transformed keratinocytes and cervical cancer cell lines compared to primary keratinocytes. Mature miRNAs derived from hsa-mir-129-2, -137, -3663, and -3665 decreased anchorage independence in cervical cancer cell lines. Finally, significantly increased methylation of hsa-mir-129-2, -935, -3663, -3665, and -4281 was observed in cervical (pre)cancerous lesions, underlining the clinical relevance of our findings. In conclusion, methylation-mediated silencing of tumour suppressive miRNAs contributes to the acquisition of anchorage independence, supporting the importance of miRNAs during early stages of carcinogenesis and underlining their potential as both disease markers and therapeutic targets.