Figure 5.

Inhibition of the vemurafenib-dependent degradome in HrasA5 SEs by suppressing MMP activity. (A) H&E-stained HrasA5-SEs under vemurafenib (5 µM) exhibit an invasive phenotype with signs of subepithelial disintegration under the invading pegs (left, arrow), a physiological state not seen in SEs treated in addition with the MMP inhibitor ilomastat (10 µM) (right). (B) Staining for the BM-components LAM (red, above) and ColVII (green, bottom) points to a pronounced degradation upon vemurafenib (middle) when compared with untreated control SEs (left). Additional application of ilomastat prevents proteolysis and allows for an uninterrupted BM (right). Likewise, delayed onset of KRT10 expression (green, middle, above) is widely renormalized by ilomastat (right, above). (C) Beyond the BM, also the subepithelial extracellular matrix is affected by the increased proteolytic activity. Picrosirius red staining visualizes semiquantitatively the amount of stromal collagen in bright field microscopy (above) and even more clearly in circular polarization microscopy that specifically highlights organized collagen bundles (bottom). Whereas under vemurafenib the density of collagen fibers is drastically reduced to 48.80% (middle), cotreatment with ilomastat completely preserves the control state (100.85% vs. 100%, right vs. left). Scale bar = 300 µM.