Cooperativity between stromal cytokines drives the invasive migration of human breast cancer cells.

The cross-talk between cancer cells and the stromal microenvironment plays a key role in regulating cancer invasion. Here, we employed an ex vivo invasion model system for exploring the regulation of breast cancer cells infiltration into a variety of stromal fibroblast monolayers. Our results revealed considerable variability in the stromal induction of invasiveness, with some lines promoting and others blocking invasion. It was shown that conditioned medium (CM), derived from invasion-promoting fibroblasts, can induce epithelial-mesenchymal transition-like process in the cancer cells, and trigger their infiltration into a monolayer of invasion-blocking fibroblasts. To identify the specific invasion-promoting molecules, we analysed the cytokines in stimulatory CM, screened a library of purified cytokines for invasion-promoting activity and tested the effect of specific inhibitors of selected cytokine receptors on the CM-induced invasion. Taken together, these experiments indicated that the invasiveness of BT-474 is induced by the combined action of IL1 and IL6 and that IL1 can induce IL6 secretion by invasion-blocking fibroblasts, thereby triggering cancer cell invasion into the stroma. This unexpected observation suggests that stromal regulation of cancer invasion may involve not only cross-talk between stromal and cancer cells, but also cooperation between different stromal subpopulations. This article is part of a discussion meeting issue 'Forces in cancer: interdisciplinary approaches in tumour mechanobiology'.

Altered p53 functionality in cancer-associated fibroblasts contributes to their cancer-supporting features.

Within the tumor microenvironment, cancer cells coexist with noncancerous adjacent cells that constitute the tumor microenvironment and impact tumor growth through diverse mechanisms. In particular, cancer-associated fibroblasts (CAFs) promote tumor progression in multiple ways. Earlier studies have revealed that in normal fibroblasts (NFs), p53 plays a cell nonautonomous tumor-suppressive role to restrict tumor growth. We now wished to investigate the role of p53 in CAFs. Remarkably, we found that the transcriptional program supported by p53 is altered substantially in CAFs relative to NFs. In agreement, the p53-dependent secretome is also altered in CAFs. This transcriptional rewiring renders p53 a significant contributor to the distinct intrinsic features of CAFs, as well as promotes tumor cell migration and invasion in culture. Concordantly, the ability of CAFs to promote tumor growth in mice is greatly compromised by depletion of their endogenous p53. Furthermore, cocultivation of NFs with cancer cells renders their p53-dependent transcriptome partially more similar to that of CAFs. Our findings raise the intriguing possibility that tumor progression may entail a nonmutational conversion ("education") of stromal p53, from tumor suppressive to tumor supportive.

Dual role of E-cadherin in the regulation of invasive collective migration of mammary carcinoma cells.

In this article, we explore a non-canonical form of collective cell migration, displayed by the metastatic murine mammary carcinoma cell line 4T1. We show here that in sparsely plated 4T1 cells, E-cadherin levels are moderately reduced (~50%), leading to the development of collective migration, whereby cells translocate in loose clusters, interconnected by thin membrane tethers. Knocking down E-cadherin blocked tether formation in these cells, leading to enhancement of migration rate and, at the same time, to suppression of lung metastases formation in vivo, and inhibition of infiltration into fibroblast monolayers ex vivo. These findings suggest that the moderate E-cadherin levels present in wild-type 4T1 cells play a key role in promoting cancer invasion and metastasis.

The role of Vimentin in Regulating Cell Invasive Migration in Dense Cultures of Breast Carcinoma Cells.

Cell migration and mechanics are tightly regulated by the integrated activities of the various cytoskeletal networks. In cancer cells, cytoskeletal modulations have been implicated in the loss of tissue integrity and acquisition of an invasive phenotype. In epithelial cancers, for example, increased expression of the cytoskeletal filament protein vimentin correlates with metastatic potential. Nonetheless, the exact mechanism whereby vimentin affects cell motility remains poorly understood. In this study, we measured the effects of vimentin expression on the mechano-elastic and migratory properties of the highly invasive breast carcinoma cell line MDA231. We demonstrate here that vimentin stiffens cells and enhances cell migration in dense cultures, but exerts little or no effect on the migration of sparsely plated cells. These results suggest that cell-cell interactions play a key role in regulating cell migration, and coordinating cell movement in dense cultures. Our findings pave the way toward understanding the relationship between cell migration and mechanics in a biologically relevant context.

The general phosphotransferase system proteins localize to sites of strong negative curvature in bacterial cells.

UNLABELLED: The bacterial cell poles are emerging as subdomains where many cellular activities take place, but the mechanisms for polar localization are just beginning to unravel. The general phosphotransferase system (PTS) proteins, enzyme I (EI) and HPr, which control preferential use of carbon sources in bacteria, were recently shown to localize near the Escherichia coli cell poles. Here, we show that EI localization does not depend on known polar constituents, such as anionic lipids or the chemotaxis receptors, and on the cell division machinery, nor can it be explained by nucleoid occlusion or localized translation. Detection of the general PTS proteins at the budding sites of endocytotic-like membrane invaginations in spherical cells and their colocalization with the negative curvature sensor protein DivIVA suggest that geometric cues underlie localization of the PTS system. Notably, the kinetics of glucose uptake by spherical and rod-shaped E. coli cells are comparable, implying that negatively curved "pole-like" sites support not only the localization but also the proper functioning of the PTS system in cells with different shapes. Consistent with the curvature-mediated localization model, we observed the EI protein from Bacillus subtilis at strongly curved sites in both B. subtilis and E. coli. Taken together, we propose that changes in cell architecture correlate with dynamic survival strategies that localize central metabolic systems like the PTS to subcellular domains where they remain active, thus maintaining cell viability and metabolic alertness. IMPORTANCE: Despite their tiny size and the scarcity of membrane-bounded organelles, bacteria are capable of sorting macromolecules to distinct subcellular domains, thus optimizing functionality of vital processes. Understanding the cues that organize bacterial cells should provide novel insights into the complex organization of higher organisms. Previously, we have shown that the general proteins of the phosphotransferase system (PTS) signaling system, which governs utilization of carbon sources in bacteria, localize to the poles of Escherichia coli cells. Here, we show that geometric cues, i.e., strong negative membrane curvature, mediate positioning of the PTS proteins. Furthermore, localization to negatively curved regions seems to support the PTS functionality.

Spatial and temporal organization of the E. coli PTS components.

The phosphotransferase system (PTS) controls preferential use of sugars in bacteria. It comprises of two general proteins, enzyme I (EI) and HPr, and various sugar-specific permeases. Using fluorescence microscopy, we show here that EI and HPr localize near the Escherichia coli cell poles. Polar localization of each protein occurs independently, but HPr is released from the poles in an EI- and sugar-dependent manner. Conversely, the ß-glucoside-specific permease, BglF, localizes to the cell membrane. EI, HPr and BglF control the ß-glucoside utilization (bgl) operon by modulating the activity of the BglG transcription factor; BglF inactivates BglG by membrane sequestration and phosphorylation, whereas EI and HPr activate it by an unknown mechanism in response to ß-glucosides availability. Using biochemical, genetic and imaging methodologies, we show that EI and HPr interact with BglG and affect its subcellular localization in a phosphorylation-independent manner. Upon sugar stimulation, BglG migrates from the cell periphery to the cytoplasm through the poles. Hence, the PTS components appear to control bgl operon expression by ushering BglG between the cellular compartments. Our results reinforce the notion that signal transduction in bacteria involves dynamic localization of proteins.