Genome functional screening identifies GAB2 as a key promoter of anchorage independence in normal and neoplastic cells. Homo sapiens

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. Overall design: Experiment I ("Xenoarray"), 8 samples (GSM455814-GSM455821): four control sample transduced with GFP, of which two selected for growth in the absence of anchorage, and four samples transduced with a mouse testis retroviral expression library, of which two selected for growth in the absence of anchorage. The cells are human, the expression arrays are murine to trace the abundance of library-derived murine transcripts before and after selection. Experiment II, 12 samples (GSM455826-GSM455837): biological duplicates of MCF10A cells in six different experimental conditions.