UV-induced EGFR signal transactivation is dependent on proligand shedding by activated metalloproteases in skin cancer cell lines.
ABSTRACT Exposure to extensive ultraviolet (UV) rays is a major cause of skin cancer, which is thought to be initiated by DNA mutations. Members of the epidermal growth factor receptor (EGFR) family are important in various pathophysiologic processes like cancer and are shown to be phosphorylated upon UV exposure. Here we show that EGFR phosphorylation by modest UV doses is dependent on metalloprotease activity and resultant epidermal growth factor (EGF) family proligand shedding. This proligand cleavage releases the mature ligand, which then binds to and activates EGFR. We show that UV induced EGFR phosphorylation in transformed cell lines of melanocyte and keratinocyte origin, which was reduced upon preincubation with a broad-spectrum metalloprotease inhibitor, BB94. UV also activated EGFR downstream signaling via Erk and Akt pathways in a BB94-sensitive manner. Furthermore, using neutralizing antibodies we found that proligand amphiregulin was required for UV-induced EGFR activation in SCC-9 cells. Using RNAi this EGFR activation was further shown to depend on the metalloproteases ADAM9 and ADAM17 in SCC-9 cells. cDNA array hybridization and RT-PCR analysis showed overexpression of a Disintegrin and a Metalloproteases (ADAMs) and EGF family proligands in melanoma cell lines. Additionally, blocking EGFR signal transactivation by BB94 led to increased apoptosis in UV-irradiated cells. EGFR signal transactivation also led to increased stability of the DNA repair protein, PARP, under UV stress. Thus, both antiapoptotic and DNA repair pathways are activated simultaneously by EGFR signal transactivation. Together, our data provide novel insights into the mechanism of UV-induced EGFR activation, suggesting broad relevance of the UV-ADAM-proligand-EGFR-Erk/Akt pathway and its significance in skin cancer.
Article: Ultraviolet B-induced expression of amphiregulin and growth differentiation factor 15 in human lens epithelial cells.[show abstract] [hide abstract]
ABSTRACT: Epidemiological and experimental studies have revealed that exposure to ultraviolet B (UVB) light can induce cataractogenesis. The objective of this study was to determine gene expression changes in human lens epithelial cells in response to UVB exposure and identify factors that can be involved in UVB-induced cataractogenesis. SV40 T-antigen-transformed human lens epithelial cells (SRA01/04) were irradiated at various UVB-energy levels (10-80 mJ/cm²) and checked for viability. An irradiation condition of 30 mJ/cm² was adopted for transcriptome analysis. Total RNAs isolated from UVB-exposed and unexposed cells at 12 h and 24 h after UVB exposure were examined for global gene expression changes using Affymetrix Human Gene 1.0 ST array. mRNA levels of specific genes were examined by RT-PCR and real-time PCR, and protein levels in the conditioned media were assayed by ELISA. To examine mRNA expression in human lens, primary cultured human lens epithelial (HLE) cells were prepared from surgically removed lens epithelium, and used for UVB-irradiation and expression analysis. Effects of certain gene products on SRA01/04 cell metabolism were examined using commercially available recombinant proteins. Expression of most the genes analyzed was essentially unchanged (between 0.5 and 2.0 fold) in UVB-irradiated cells compared to non-irradiated cells at both 12 and 24 h after UVB exposure. Sixty one and 44 genes were upregulated more than twofold by UVB exposure at 12 h and 24 h, respectively. Emphasis was placed on genes encoding extracellular proteins, especially growth factors and cytokines. A total of 18 secreted protein genes were upregulated more than twofold at either or both time points. Amphiregulin (AREG) and growth differentiation factor 15 (GDF15) were chosen because of their higher upregulation and novelty, and their upregulation was confirmed in SRA01/04 cells using RT-PCR and real-time PCR analysis. AREG and GDF15 protein levels in conditioned media significantly increased at all UVB-energy points at 24 h, while they were scarcely detectable at 12 h. AREG and GDF15 mRNA levels were also significantly upregulated in UVB-irradiated primary cultured HLE cells compared with the corresponding control culture. AREG significantly stimulated ³H-thymidine and ³H-leucine uptake in SRA01/04 cells as did a positive control epidermal growth factor (EGF). Recombinant GDF15 did not stimulate ³H-thymidine incorporation at any concentration tested, but significantly stimulated ³H-leucine uptake. RT-PCR analysis demonstrated that primary cultured HLE and SRA01/04 cells expressed not only epidermal growth factor receptor (EGFR) mRNA but also transforming growth factor β receptors (TGFBR1 and TGFBR2) mRNAs. These results indicate that AREG and GDF15 produced in response to UVB exposure can affect the growth and protein synthesis of lens epithelial cells, suggesting that they have autocrine and paracrine roles related to pathological changes of lens tissue during long-term UVB exposure.Molecular vision 01/2011; 17:159-69. · 2.20 Impact Factor
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ABSTRACT: A disintegrin and metalloproteinases (ADAMs) are members of a new gene family of transmembrane and secreted proteins, which belong to the zinc proteinase superfamily. These molecules are involved in various biological events such as cell adhesion, cell fusion, cell migration, membrane protein shedding, and proteolysis. Growing evidence now attests to the potential involvement of ADAMs proteinases in diverse processes such as skin wound healing, inflammation, pigmentation, tumor development, cell proliferation, and metastasis. This paper focuses on the roles of ADAMs proteinases in a wide variety of skin diseases.Enzyme research. 01/2011; 2011:482498.
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ABSTRACT: The ADAMs are transmembrane proteins implicated in proteolysis and cell adhesion. Forty gene members of the family have been identified, of which 21 are believed to be functional in humans. As proteases, their main substrates are the ectodomains of other transmembrane proteins. These substrates include precursor forms of growth factors, cytokines, growth factor receptors, cytokine receptors and several different types of adhesion molecules. Although altered expression of specific ADAMs has been implicated in different diseases, their best-documented role is in cancer formation and progression. ADAMs shown to play a role in cancer include ADAM9, ADAM10, ADAM12, ADAM15 and ADAM17. Two of the ADAMs, i.e., ADAM10 and 17 appear to promote cancer progression by releasing HER/EGFR ligands. The released ligands activate HER/EGFR signalling that culminates in increased cell proliferation, migration and survival. Consistent with a causative role in cancer, several ADAMs are emerging as potential cancer biomarkers for aiding cancer diagnosis and predicting patient outcome. Furthermore, a number of selective ADAM inhibitors, especially against ADAM10 and ADAM17, have been shown to have anti-cancer effects. At least one of these inhibitors is now undergoing clinical trials in patients with breast cancer.Clinical Proteomics 01/2011; 8(1):9.