Positive Quantitative Relationship between EMT and Contact-Initiated Sliding on Fiber-like Tracks

Abstract

Epithelial-mesenchymal transition (EMT) is a complex process by which cells acquire invasive properties that enable escape from the primary tumor. Complete EMT, however, is not required for metastasis: circulating tumor cells exhibit hybrid epithelial-mesenchymal states, and genetic perturbations promoting partial EMT induce metastasis in vivo. An open question is whether and to what extent intermediate stages of EMT promote invasiveness. Here, we investigate this question, building on recent observation of a new invasive property. Migrating cancer cell lines and cells transduced with prometastatic genes slide around other cells on spatially confined, fiberlike micropatterns. We show here that low-dosage/short-duration exposure to transforming growth factor beta (TGFβ) induces partial EMT and enables sliding on narrower (26 μm) micropatterns than untreated counterparts (41 μm). High-dosage/long-duration exposure induces more complete EMT, including disrupted cell-cell contacts and reduced E-cadherin expression, and promotes sliding on the narrowest (15 μm) micropatterns. These results identify a direct and quantitative relationship between EMT and cell sliding and show that EMT-associated invasive sliding is progressive, with cells that undergo partial EMT exhibiting intermediate sliding behavior and cells that transition more completely through EMT displaying maximal sliding. Our findings suggest a model in which fiber maturation and EMT work synergistically to promote invasiveness during cancer progression.

Figure 1

(A–L) Cell morphology changes induced by TGFβ treatment. Nontransformed mammary epithelial MCF-10A cells were treated with TGFβ or left untreated. Treated cells were exposed to either 5 or 20 ng/mL of TGFβ for between 3 and 12 days. (Asterisks) Cells with an elongated, mesenchymal morphology. (Arrowheads) Deficient cell-cell adhesions. Phase contrast images were taken before cell passage at 10× magnification.

Figure 2

Extent of TGFβ-induced EMT. (A) E-cadherin expression was measured by Western blot in TGFβ-treated and untreated (control) cells. Erk2 was probed as an equal-loading control. (B) Quantification of the ratio of E-cadherin/Erk expression for cells treated with 5 ng/mL (triangle) or 20 ng/mL (circle) TGFβ. Values are reported relative to the E-cadherin/Erk expression ratio for untreated cells. Two-way ANOVA indicates that the dependence of E-cadherin expression on time of exposure is statistically significant (p < 0.05), whereas the effect of dose is not statistically distinguishable. Error bars denote SD.

Figure 3

Collision response as a function of TGFβ treatment. (A) Fraction sliding and (B) CFD for TGFβ-treated and untreated (control, square) cells. MCF-10A cells were treated with either 5 ng/mL TGFβ (triangle) for three days (solid representation, solid line) or six days (open, dashed line); and 20 ng/mL TGFβ (circle) for three days (solid representation, solid line) or 12 days (open, dashed line). In total, 7226 cell-cell collisions were analyzed across all 50 combinations of five TGFβ treatment conditions and 10 micropattern widths (detailed breakdown of sample sizes provided in Table S2). For each TGFβ treatment condition, including control, the dependence of fraction sliding on line width is statistically significant (p < 0.001). Meanwhile, the dependence of fraction sliding on TGFβ treatment was statistically significant at line widths of 12 μm (p < 0.001) and 9, 15, 21, 27, and 33 μm (p < 0.05). The dependence of fraction sliding on TGFβ treatment at line widths of 6, 18, 24, and 30 μm were not statistically significant. Further details on analysis of variance are provided in the Supporting Material. Error bars denote mean ± SE.

Figure 4

TGFβ-induced EMT promotes two regimes of invasive behavior. E-cadherin expression (solid squares, left y axis) and CFD values (solid circles, right y axis) are plotted for cells left untreated or treated with different doses and durations of TGFβ (x axis). Error bars denote SD for E-cadherin expression and the 95% confidence interval for CFD.