Genetic changes in HER2, PTEN, PIK3CA and AKT1 are all common in breast cancer and lead to the elevated phosphorylation of downstream targets of the PI3K/AKT signalling pathway. Changes in HER2, PTEN, PIK3CA and AKT have all been reported to lead to both enhanced proliferation and failures in hollow lumen formation in three dimensional epithelial culture models, but it is not clear whether these failures in lumen formation are caused by any failure in the spatial coordination of lumen formation (hollowing) or purely a failure in the apoptosis and clearance of luminal cells (cavitation). Here we use NMuMG mammary epithelial cells, which form a hollow lumen without significant apoptosis, to compare the transformation by these four genetic changes. We find that either mutant PIK3CA expression or PTEN loss, but not mutant AKT1 E17K, cause disrupted epithelial architecture, whereas HER2 over-expression drives strong proliferation without affecting lumen formation in these cells. We also show that PTEN requires both lipid and protein phosphatase activity, its extreme C-terminal PDZ binding sequence and probably Myosin 5A to control lumen formation through a mechanism that does not correlate with its ability to control AKT, but which is selectively lost through mutation in some tumours. These findings correlate AKT independent signalling activated by mutant PIK3CA or PTEN loss, but not strongly by HER2, with disrupted epithelial architecture and tumour formation.

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BackgroundWith the completion of the whole genome sequence for many organisms, investigations into genomic structure have revealed that gene distribution is variable, and that genes with similar function or expression are located within clusters. This clustering suggests that there are evolutionary constraints that determine genome architecture. However, as most of the evidence for constraints on genome evolution comes from studies on yeast, it is unclear how much of this prior work can be extrapolated to mammalian genomes. Therefore, in this work we wished to examine the constraints on regions of the mammalian genome containing conserved gene clusters.ResultsWe first identified regions of the mouse genome with microsynteny conservation by comparing gene arrangement in the mouse genome to the human, rat, and dog genomes. We then asked if any particular gene types were found preferentially in conserved regions. We found a significant correlation between conserved microsynteny and the density of mouse orthologs of human disease genes, suggesting that disease genes are clustered in genomic regions of increased microsynteny conservation.ConclusionThe correlation between microsynteny conservation and disease gene locations indicates that regions of the mouse genome with microsynteny conservation may contain undiscovered human disease genes. This study not only demonstrates that gene function constrains mammalian genome organization, but also identifies regions of the mouse genome that can be experimentally examined to produce mouse models of human disease.