aPKCi triggers basal extrusion of luminal mammary epithelial cells by tuning contractility and vinculin localization at cell junctions

Abstract

SignificanceThis study shows that an oncogenic mammary epithelial cell surrounded by normal cells can extrude basally in vivo and invade surrounding tissues without formation of a primary tumor. Here, we show that overexpression of the key polarity protein atypical protein kinase C ι (aPKCi) is sufficient for triggering basally oriented epithelial cell extrusion and early cell invasion into the mammary gland stroma. Moreover, we highlight the importance of the difference between the mechanical properties of aPKCi-overexpressing cells and those of the normal surrounding cells associated with the decrease of vinculin at the cell junction, which triggers cell segregation, the first step toward promoting and controlling the direction of cell extrusion.

A new analytical pipeline for the study of the onset of mammary gland oncogenesis based on mammary organoid transplantation and organ clearing

“…All GFP + epithelial cells were localised into the ducts (Figure 3a), whereas GFP-aPKCi + cells, positive for keratin 8, were able to breach the basement membrane ( Figure 3b -Movie 2). These data, in line with our previous study (Villeneuve et al, 2019), show that GFP-aPKCi + cells could leave the duct by transmigration through the basement membrane. The phospho-MLC2 staining, in combination with E-cadherin staining, allowed us to detect both the mammary ducts and the blood vessels (Figure 3c/d).…”

“…The mice were then sacrificed at the latest 5 to 10 weeks post-transplantation and the mammary glands 4 were collected. For mammary gland immunofluorescence, without clearing and reduction, tissue immunofluorescence was performed as described in (Villeneuve et al, 2019).…”

“…aPKCi is an oncogenic protein (Fields and Regala, 2007;Parker et al, 2014;Regala et al, 2005), which is overexpressed in many carcinomas; we and others reported that aPKCi overexpression is associated bad prognosis/outcome in breast cancer (Awadelkarim et al, 2012;Rosse et al, 2014). Additionally, we recently found that overexpression of aPKCi (aPKCi + ) in luminal epithelial cells is sufficient to trigger basally-oriented cell extrusion of aPKCi + cells from the normal mammary epithelium (Villeneuve et al, 2019). Although not proven, it is possible that once they have reached the stroma, basally-extruded aPKCi + cells potentially invade distant tissues.…”

“…to generate GFP or GFP-aPKCi-expressing cells at low frequency (Figure 2a). Using this strategy, we could overexpress aPKCi in a limited number of mammary luminal cells as shown in ((Villeneuve et al, 2019).…”

Dysfunctional Mechanotransduction through the YAP/TAZ/Hippo Pathway as a Feature of Chronic Disease

“…Besides loss of polarity, overexpression of aPKC in cancer has also been implicated in altering the mechanical properties of cells. Indeed, spheroids consisting of MCF10A breast cancer cells expressing aPKC have been observed to have increased surface tension [37]. Furthermore junctions between aPKC expressing and non-aPKC expressing cells bear an increased tension that allow them to actively extrude into the lamina [37].…”