Exposure to Asphalt Fumes Activates Activator Protein-1 through the Phosphatidylinositol 3-Kinase/Akt Signaling Pathway in Mouse Epidermal Cells

Abstract

Occupational exposure to asphalt fumes may pose a health risk. Experimental studies using animal and in vitro models indicate that condensates from asphalt fumes are genotoxic and can promote skin tumorigenesis. Enhanced activity of activator protein-1 (AP-1) is frequently associated with the promotion of skin tumorigenesis. The current study investigated the effect of exposure to asphalt fumes on AP-1 activation in mouse JB6 P ؉ epidermal cells and the skin of transgenic mice expressing the AP-1 luciferase reporter gene. Asphalt fumes were generated from a dynamic generation system that simulated road-paving conditions. Exposure to asphalt fumes significantly increased AP-1 activity in JB6 P ؉ cells as well as in cultured keratinocytes isolated from transgenic mice expressing AP-1 reporter. In addition, topical application of asphalt fumes by painting the tail skin of mice increased AP-1 activity by 14-fold. Exposure to asphalt fumes promoted basal as well as epidermal growth factor-stimulated anchorage-independent growth of JB6 P ؉ cells in soft agar. It activated phosphatidylinositol 3-kinase and induced phosphorylation of Akt at Ser-473/Thr-308, and concurrently activated downstream p70 S6 kinase as well as glycogen synthase kinase-3␤. Asphalt fumes transiently activated c-Jun NH 2 -terminal kinases without affecting extracellular signal-regulated kinases and p38 mitogen-activated protein kinases. Further study indicated that blockage of phosphatidylinositol 3-kinase activation eliminated asphalt fume-stimulated AP-1 activation and formation of anchorage-independent colonies in soft agar. This is the first report showing that exposure to asphalt fumes can activate AP-1 and intracellular signaling that may promote skin tumorigenesis, thus providing important evidence on the potential involvement of exposure to asphalt fumes in skin carcinogenesis.

Collagen I induction by high glucose levels is mediated by epidermal growth factor receptor and phosphoinositide 3-kinase/Akt signalling in mesangial cells

“…In endothelial cells, insulin-induced AP-1 activation was blocked by PI3K inhibition with wortmannin [36]. PI3K activation by asphalt fumes mediated AP-1 activation in epidermal cells [37]. Overexpression of a dominantnegative p85 construct in fibroblasts prevented growth factor-induced expression of c-fos, a component of the heterodimeric AP-1 [38].…”

Silibinin Up-regulates DNA-Protein Kinase-dependent p53 Activation to Enhance UVB-induced Apoptosis in Mouse Epithelial JB6 Cells

“…It has also been reported that in response to UVB, Akt/PKB is phosphorylated at Ser 473 by upstream kinases such as PI 3-kinase and DNA-PK (44); Ser 473 phosphorylation of Akt is essential for its kinase activity (45,46). Although Akt activation is known as a survival and anti-apoptotic response, in the present study, we found that silibinin enhances UVB-induced Akt activation, which appears to be a stress response consistent with recent reports showing that Akt is one of the substrates of DNA-PK, a genotoxic stress response gene (44).…”

The Role of Glycogen Synthase Kinase 3β in the Transformation of Epidermal Cells

“…These cells form colonies in soft agar and display tumorigenicity in vivo. The stable transfectants of JB6 P+ cells expressing AP-1-luciferase reporter (Cl 41 AP-1) have been previously described (17,18).…”

“…The immunoblotting procedure to detect phosphorylation and expression of signal proteins was done as previously described (17). To control for the loading, the blots were stripped and reprobed with an antiactin antibody (Santa Cruz Biotechnology).…”

“…Anchorage-independent growth of JB6 P+, JB7 cells, and stable transfectants expressing various GSK3h constructs was determined by a previously described method (17). The cell growth matrix consists of two layers of basal medium Eagle (BME) agar in six-well culture trays.…”