Fibroblast-to-myofibroblast switch is mediated by NAD(P)H oxidase generated reactive oxygen species

Tumour-stroma interaction is a prerequisite for tumour progression in skin cancer. Hereby, a critical step in stromal function is the transition of tumour-associated fibroblasts to MFs (myofibroblasts) by growth factors, for example TGF beta (transforming growth factor beta(). In this study, the question was addressed of whether fibroblast-associated NAD(P) H oxidase (NADH/NADPH oxidase), known to be activated by TGF beta 1, is involved in the fibroblast-to-MF switch. The up-regulation of alpha SMA (alpha smooth muscle actin), a biomarker for MFs, is mediated by a TGF beta 1-dependent increase in the intracellular level of ROS (reactive oxygen species). This report demonstrates two novel aspects of the TGF beta 1 signalling cascade, namely the generation of ROS due to a biphasic NAD(P) H oxidase activity and a ROS-dependent downstream activation of p38 leading to a transition of dermal fibroblasts to MFs that can be inhibited by the selective NAD(P)H oxidase inhibitor apocynin. These data suggest that inhibition of NAD(P)H oxidase activity prevents the fibroblast-to-MF switch and may be important for chemoprevention in context of a 'stromal therapy' which was described earlier.