Metastatic cancer cells exert greater forces than non-metastatic cells.

<p>(A) Representative traction maps (<i>left</i>), corresponding phase images (<i>middle</i>), and overall net traction force (|<i>F</i>|, <i>right</i>) of non-metastatic mammary epithelial (MCF10A) and highly metastatic (MDAMB231) cancer cells. (B) Representative traction maps (<i>left</i>), corresponding phase images (<i>middle</i>), and |<i>F</i>| (<i>right</i>) of non-metastatic primary prostate epithelial cells (PrEC) and highly metastatic prostate cancer cells (PC3). (C) Representative traction maps (<i>left</i>), corresponding phase images (<i>middle</i>), and |<i>F</i>| (<i>right</i>) of non-metastatic bronchial epithelial cells (BEAS2B) and metastatic lung adenocarcinoma cells (A549). All cells are on polyacrylamide substrates with Young's Modulus (E) = 5 kPa and type I collagen concentration of 0.1 mg/mL. Scale bar = 50 µm. Mean+SEM; *** indicates p<0.001.</p

Metastatic derivative in a series of isogenic cell lines exerts greater forces.

<p>(A) Phase images of parental untransformed cells (MCF10A), transformed premalignant (MCF10AT1) and highly metastatic (MCF10CA1a) derivatives. (B) Net traction forces increase with increasing metastatic potential, with the highest forces exerted by the metastatic MCF10CA1a cells. (C) Average traction stress (|<i>F</i>|/A) increases with increasing metastatic potential. Mean ± SEM; ** indicates p<0.01; *** indicates p<0.001.</p

Cell area is differentially altered by matrix stiffness and collagen density.

<p>Projected cell area shows a biphasic relationship with substrate stiffness (A) and a direct relationship with collagen density (B) in the majority of the metastatic (black) and non-metastatic cells (white) studied. No consistent trend was observed when comparing the projected cell area of complementary metastatic and non-metastatic cells.</p

Average traction stress increases with stiffness, not collagen density.

<p>|<i>F</i>| of each cell is normalized by its projected area (|<i>F</i>|/A) as a measurement of average traction stress. Average traction stresses increase with increasing substrate stiffness (A) but become relatively uniform with increasing collagen density (B) in both metastatic (black) and non-metastatic (white) cells studied.</p

Increased matrix stiffness contributes to increased force generation.

<p>Net traction force (|<i>F</i>|) increases with increasing substrate stiffness (E = 1–10 kPa) for (A) MCF10A non-metastatic mammary epithelial cells and MDAMB231 metastatic cancer cells, (B) PrEC non-metastatic primary prostate epithelial cells and PC3 metastatic prostate cancer cells, and (C) BEAS2B non-metastatic bronchial epithelial cells and A549 metastatic lung cancer cells. Ligand density is maintained at 0.1 mg/mL collagen I. 5 kPa data is from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032572#pone-0032572-g001" target="_blank">Figure 1</a>. Note also that the metastatic cancer cells (black) exert greater forces than non-metastatic cells (white) at all matrix stiffness levels studied. Mean+SEM; * indicates p<0.05; *** indicates p<0.001.</p