The zinc-finger transcription factor Snail1 is inappropriately expressed in breast cancer and associated with poor prognosis. While interrogating human databases, we uncovered marked decreases in relapse-free survival of breast cancer patients expressing high Snail1 levels in tandem with wild-type, but not mutant, p53. Using a Snail1 conditional knockout model of mouse breast cancer that maintains wild-type p53, we find that Snail1 plays an essential role in tumour progression by controlling the expansion and activity of tumour-initiating cells in preneoplastic glands and established tumours, whereas it is not required for normal mammary development. Growth and survival of preneoplastic as well as neoplastic mammary epithelial cells is dependent on the formation of a Snail1/HDAC1/p53 tri-molecular complex that deacetylates active p53, thereby promoting its proteasomal degradation. Our findings identify Snail1 as a molecular bypass that suppresses the anti-proliferative and pro-apoptotic effects exerted by wild-type p53 in breast cancer.

We have developed a 4D computer-assisted reconstruction and motion analysis system, J3D-DIAS 4.1, and applied it to the reconstruction and motion analysis of tumorigenic cells in a 3D matrix. The system is unique in that it is fast, high-resolution, acquires optical sections using DIC microscopy (hence there is no associated photoxicity), and is capable of long-term 4D reconstruction. Specifically, a z-series at 5 μm increments can be acquired in less than a minute on tissue samples embedded in a 1.5 mm thick 3D Matrigel matrix. Reconstruction can be repeated at intervals as short as every minute and continued for 30 days or longer. Images are converted to mathematical representations from which quantitative parameters can be derived. Application of this system to cancer cells from established lines and fresh tumor tissue has revealed unique behaviors and cell types not present in non-tumorigenic lines. We report here that cells from tumorigenic lines and tumors undergo rapid coalescence in 3D, mediated by specific cell types that we have named “facilitators” and “probes.” A third cell type, the “dervish”, is capable of rapid movement through the gel and does not adhere to it. These cell types have never before been described. Our data suggest that tumorigenesis in vitro is a developmental process involving coalescence facilitated by specialized cells that culminates in large hollow spheres with complex architecture. The unique effects of select monoclonal antibodies on these processes demonstrate the usefulness of the model for analyzing the mechanisms of anti-cancer drugs.

SummaryUsing a newly developed microfluidic chamber, we have demonstrated in vitro that Ca 2+ functions as a chemoattractant of aggregationcompetent Dictyostelium discoideum amoebae, that parallel spatial gradients of cAMP and Ca 2+ are more effective than either alone, and that cAMP functions as a stronger chemoattractant than Ca 2+ . Effective Ca 2+ gradients are extremely steep compared with effective cAMP gradients. This presents a paradox because there is no indication to date that steep Ca 2+ gradients are generated in aggregation territories. However, given that Ca 2+ chemotaxis is co-acquired with cAMP chemotaxis during development, we speculate on the role that Ca 2+ chemotaxis might have and the possibility that steep, transient Ca 2+ gradients are generated during natural aggregation in the interstitial regions between cells.

During aggregation of Dictyostelium discoideum, nondissipating, symmetric,outwardly moving waves of cAMP direct cells towards aggregation centers. It has been assumed that the spatial and temporal characteristics of the front and back of each cAMP wave regulate both chemokinesis and chemotaxis. However, during the period preceding aggregation, cells acquire not only the capacity to chemotax in a spatial gradient of cAMP, but also in a spatial gradient of Ca++. The null mutant of the putative iplACa++ channel gene, iplA-, undergoes normal chemotaxis in spatial gradients of cAMP and normal chemokinetic responses to increasing temporal gradients of cAMP, both generated in vitro. However, iplA-cells lose the capacity to undergo chemotaxis in response to a spatial gradient of Ca++, suggesting that IplA is either the Ca++ chemotaxis receptor or an essential component of the Ca++ chemotaxis regulatory pathway. In response to natural chemotactic waves generated by wild type cells, the chemokinetic response of iplA- cells to the temporal dynamics of the cAMP waveis intact, but the capacity to reorient in the direction of the aggregation center at the onset of each waveis lost. These results suggest a model in which transient Ca++ gradients formed between cells at the onset of each natural cAMP wave augment reorientation towards the aggregation center. If this hypothesis proves correct, it will provide a more complex contextual framework for interpreting D. discoideum chemotaxis.