E2+PRL induces invasion only in high density/ stiff collagen matrices.

<p><b>a)</b> MCF-7 cells were cultured in LD or HD collagen on 8µm transwell inserts, treated for 24hr with EtOH vehicle ± 2nM E2, ± 8nM PRL as indicated, and transversed cells were counted. n = 3. Asterisks indicate significant differences between the same treatments in different densities, *p<0.05, ***p<0.001. Different letters represent significant differences (p<0.05) between treatments within each matrix density condition. <b>b)</b> MCF-7 cells were cultured in LD or HD collagen and treated +/- 1nM E2, ± 4nM PRL for 72h. SHG images were collected and analyzed as described in the Materials and Methods. n = 7–8, *p<0.05. c) Representative heat maps of angles of collagen fibers relative to boundaries of cells cultured in low and high matrix densities co-treated with estrogen and PRL. Clear (black) areas represent 0–15 degrees; green, 15–45 degrees; yellow, 45–60 degrees; red, 60–90 degrees.