The role of vitamin D signalling in the interaction between mesenchymal mammary tumour cells and macrophages

The transition of epithelial-like tumour cells to those exhibiting mesenchymal characteristics (Epithelial-to-mesenchymal Transition; EMT) is an integral process in breast cancer metastasis. EMT can be promoted by Transforming growth factor-beta (TGF-β) which can be found at high levels in the tumour stroma. Tumour-associated macrophages (TAMs) can also induce EMT in breast cancer cells, which is one way that they promote breast cancer metastasis. Vitamin D signalling has been implicated in EMT suppression and plays a role in modulating macrophage differentiation and stimulating their anti-inflammatory functions. This project had two major aims. First, we aimed to create and verify a unique fluorescent reporter gene construct designed to evaluate the dynamics of EMT in real-time and at the single-cell level. While some components of this reporter system were successfully validated, work to complete the final reporter construct is ongoing. The second and main aspect of this project focused on exploring the ability of 1,25-dihydroxyvitamin D3 (1,25D3) to modulate the interaction between mesenchymal mammary tumour cells and TAMs. Unexpectedly, in short-term treatment (48 hours) studies of 4T1 murine mammary tumour cells, we observed that 1,25D3 and TGF-β signalling work together to increase expression of the mesenchymal markers, Snai1, Fn1, and Col1a1. 1,25D3 and TGF-β also synergistically activate transcription of the gene encoding the 1,25D3-catabolizing enzyme, Cyp24a1. The ability of 1,25D3 and TGF-β to enhance expression of these genes was diminished in a long-term treatment (14 days) of 4T1 cells, and this effect was accompanied by a decrease in cell proliferation. 1,25D3 may also cooperate with cytokines produced by normal macrophages and macrophages considered to be TAM-like. Conditioned media experiments revealed that in the presence of factors from normal macrophages, 1,25D3 enhanced expression of Fn1, and in the presence of factors from TAM-like macrophages, 1,25D3 enhanced expression of Fn1 and Cyp24a1. Rather than mitigating the interaction as hypothesized, 1,25D3 may exacerbate the tumour-promoting effects of the EMT-TAM relationship. Also, signalling pathways involved in the EMT-TAM relationship may synergize with 1,25D3 to upregulate Cyp24a1 expression. These findings are important for understanding the potential of vitamin D compounds to be used in the treatment of breast cancer.

Late-Holocene Mass Movements in High Arctic East Lake, Melville Island (Western Canadian Arctic Archipelago)

East Lake, located at Cape Bounty (Melville Island, Canadian High Arctic), was mapped using a high-resolution swath bathymetric sonar and a 12 kHz sub-bottom profiler, allowing for the first time the imaging of widespread occurrence of mass movement deposits (MMDs) in a Canadian High Arctic Lake. Mass movements occurred mostly on steep slopes located away from deltaic sedimentation. The marine to lacustrine transition in the sediment favours the generation of mass movements where the underlying massive mud appears to act as a gliding surface for the overlying varved deposits. Based on acoustic stratigraphy, we have identified at least two distinct events that triggered failures in the lake during the last 2000 years. The synchronicity of multiple failures and their widespread distribution suggest a seismic origin that could be related to the nearby Gustaf-Lougheed Arch seismic zone. Further sedimentological investigations on the MMDs are however required to confirm their age and origin.