Abstract

Elastin peptides (EPs) produced during cancer progression bind to the elastin binding protein (EBP) found at the surface of dermal fibroblasts, leading to the expression of collagenase-1 gene. The production of this enzyme involved in stromal reaction is caused by the sustained activation of the extracellular signal-regulated kinases 1/2 (ERK1/2) pathway via cAMP/protein kinase A (PKA) and phosphatidylinositol 3-kinase (PI3K). However, the mechanism of these signaling events remains unknown. We show that κ-elastin (κE), a commonly used EP, induces maximum phosphorylation of mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK)1/2 and ERK1/2 after 30 min. The simultaneous inhibition of PKA and PI3K, by N-(2-(p-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide (H89) and 2-(4-morpholynil)-8-phenyl-4H-1-bemzopyran-4-one (LY294002), respectively, blocked MEK1/2 and ERK1/2 phosphorylation, as did lactose, an EBP antagonist. κE induced Raf-1 phosphorylation and activation in a PI3K-dependent manner. In our system, the PI3K p110γ is expressed and activated by βγ-derived subunits from a pertussis toxin-sensitive G protein after fibroblast stimulation. Pertussis toxin also blocks the Raf-1/MEK1/2/ERK1/2 phosphorylation cascade. In addition, we found that B-Raf is expressed in dermal fibroblasts and activated in a PKA-dependent manner after κE treatment, thereby integrating PKA signals to MEK1/2. It is noteworthy that Ras involvement was excluded because ERK1/2 activation by κE was not blocked in RasN17-transfected fibroblasts. Together, our results identify a novel Ras-independent ERK1/2 activation system in which p110γ/Raf-1/MEK1/2 and PKA/B-Raf/MEK1/2 cooperate to activate ERK1/2. Thus, p110γ and B-Raf seem to be important modulators of dermal fibroblasts physiology and should now qualify as therapeutic targets in strategies aiming at limiting elastin degradation contribution to cancer progression.