Polarity in breast development and cancer

Modelling Cancer Pathophysiology: Mechanisms and Changes in the Extracellular Matrix During Cancer Initiation and Early Tumour Growth

Cancer initiation and early tumour growth are complex processes influenced by multiple cellular and microenvironmental factors. A critical aspect of tumour progression is the dynamic interplay between cancer cells and the extracellular matrix (ECM), which undergoes significant alterations to support malignancy. The loss of cell polarity is an early hallmark of tumour progression, disrupting normal tissue architecture and fostering cancerous transformation. Circumstantially, cancer-associated microRNAs (miRNAs) regulate key oncogenic processes, including ECM remodelling, epithelial-to-mesenchymal transition (EMT), and tumorigenic vascular development, further driving tumour growth. ECM alterations, particularly changes in stiffness and mechanotransduction signals, create a supportive niche for cancer cells, enhancing their survival, proliferation, and invasion. EMT and its subtype, epithelial-to-endothelial transition (EET), contribute to tumour plasticity, promote the generation of cancer stem cells (CSCs), and support tumour vascularisation. Furthermore, processes of vascular development like vasculogenesis and angiogenesis are critical for sustaining early tumour growth, supplying oxygen and nutrients to hypoxic malignant cells within the evolving cancerous microenvironments. This review explores key mechanisms underlying these changes in tumorigenic microenvironments, with an emphasis on their collective role for tumour initiation and early tumour growth. It will further delve into present in vitro modelling strategies developed to closely mimic early cancer pathophysiology. Understanding these processes is crucial for developing targeted therapies aimed at disrupting key cancer-promoting pathways and improving clinical outcomes.

Plakins are involved in the regulation of centrosome position in polarized epithelial cells

BACKGROUND INFORMATION

The control of epithelial cell polarity is key to their function. Its dysregulation is a major cause of tissue transformation. In polarized epithelial cells,the centrosome is off-centred toward the apical pole. This asymmetry determines the main orientation of the microtubule network and intra-cellular traffic. However, the mechanism regulating centrosome positioning at the apical pole of polarized epithelial cells is still poorly undertood.

RESULTS

In this study we used transcriptomic data from breast cancer cells to identify molecular changes associated with the different stages of tumour transformation. We correlated these changes with variations in centrosome position or with cell progression along the epithelial-to-mesenchymal transition (EMT), a process that involves centrosome repositioning. We found that low levels of epiplakin, desmoplakin and periplakin correlated with centrosome mispositioning in cells that had progressed through EMT or tissue transformation. We further tested the causal role of these plakins in the regulation of centrosome position by knocking down their expression in a non-tumorigenic breast epithelial cell line (MCF10A). The downregulation of periplakin reduced the length of intercellular junction, which was not affected by the downregulation of epiplakin or desmoplakin. However, down-regulating any of them disrupted centrosome polarisation towards the junction without affecting microtubule stability.

CONCLUSIONS

Altogether, these results demonstrated that epiplakin, desmoplakin and periplakin are involved in the maintenance of the peripheral position of the centrosome close to inter-cellular junctions. They also revealed that these plakins are downregulated during EMT and breast cancer progression, which are both associated with centrosome mispositioning.

SIGNIFICANCE

These results revealed that the down-regulation of plakins and the consequential centrosome mispositioning are key signatures of disorganised cytoskeleton networks, inter-cellular junction weakening, shape deregulation and the loss of polarity in breast cancer cells. These metrics could further be used as a new readouts for early phases of tumoral development.