title: Cadmium induces phosphorylation and stabilization of c-Fos in HK-2 renal proximal tubular cells.
abstract: We examined the effects of cadmium chloride (CdCl₂) exposure on the expression and phosphorylation status of members of the Fos family, components of the activator protein-1 transcription factor, in HK-2 human renal proximal tubular cells. Following the exposure to CdCl₂, the expression of c-fos, fosB, fra-1, and fra-2 increased markedly, with different magnitudes and time courses. The levels of Fos family proteins (c-Fos, FosB, Fra-1, and Fra-2) also increased in response to CdCl₂ exposure. Although the elevation of c-fos transcripts was transient, c-Fos protein levels increased progressively with lower electrophoretic mobility, suggesting stabilization of c-Fos through post-translational modifications. Consistently, we observed phosphorylation of c-Fos at Ser362 and Ser374 in HK-2 cells treated with CdCl₂. Phosphorylated forms of mitogen-activated protein kinases (MAPKs)-including extracellular signal-regulated protein kinase (ERK), c-Jun NH₂-terminal kinase, and p38-increased after CdCl₂ exposure, whereas treatment with the MAPK/ERK kinase inhibitor U0126 and the p38 inhibitor SB203580 suppressed the accumulation and phosphorylation of c-Fos. We mutated Ser362 to alanine (S362A), Ser374 to alanine (S374A), and both residues to alanines (S362A/S374A) to inhibit potential phosphorylation of c-Fos at these sites. S374A or double S362A/S374A mutations reduced c-Fos level markedly, but S362A mutation did not. On the other hand, S362A/S374A mutations induced a more pronounced reduction in c-Fos DNA-binding activity than S374A mutation. These results suggest that while Ser374 phosphorylation seems to play a role in c-Fos stabilization, phosphorylation at two C-terminal serine residues is required for the transcriptional activation of c-Fos in HK-2 cells treated with CdCl₂.
authors.affiliation: Department of Hygiene and Public Health I, Tokyo Women's Medical University, 8-1 Kawada-cho, Shinjuku-ku, Tokyo 162-8666, Japan.
authors.forename: Mamiko
authors.initials: M
authors.lastname: Iwatsuki
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Inageda
authors.forename: Masato
authors.initials: M
authors.lastname: Matsuoka
mesh_terms: D019256:Cadmium Chloride / Q000633:toxicity*; D002478:Cells, Cultured; D004785:Environmental Pollutants / Q000633:toxicity*; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects*; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism; D009154:Mutation; D010766:Phosphorylation / Q000187:drug effects; D055550:Protein Stability / Q000187:drug effects; D016760:Proto-Oncogene Proteins c-fos / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors; D015533:Transcriptional Activation / Q000187:drug effects
chemical_list: D004785:Environmental Pollutants; D016760:Proto-Oncogene Proteins c-fos; D020928:Mitogen-Activated Protein Kinases; D019256:Cadmium Chloride