Quantitative Phosphoproteomic
Analysis of Early Alterations
in Protein Phosphorylation by 2,3,7,8-Tetrachlorodibenzo‑<i>p</i>‑dioxin
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Abstract
A comprehensive quantitative analysis of changes in protein
phosphorylation
preceding or accompanying transcriptional activation by 2,3,7,8-tetrachlorodibenzo-<i>p</i>-dioxin (TCDD) in 5L rat hepatoma cells was performed using
the SILAC approach. Following exposure of the cells to DMSO or 1 nM
TCDD for 0.5 to 2 h, 5648 phosphorylated peptides corresponding to
2156 phosphoproteins were identified. Eight peptides exhibited a statistically
significantly altered phosphorylation because of TCDD exposure and
22 showed a regulation factor of ≥1.5 in one of the experiments
per time point. The vast majority of the TCCD-induced phosphorylation
changes had not been reported before. The transcription factor ARNT,
the obligate partner for gene activation by the TCDD-bound Ah receptor,
exhibited an up-regulation of its Ser77 phosphorylation, a modification
known to control the differential binding of ARNT homodimers and heterodimers
to different enhancers suggesting that this phosphorylation represents
a novel mechanism contributing to the alteration of gene expression
by TCDD. Other proteins with altered phosphorylation included, among
others, various transcriptional coregulators previously unknown to
participate in TCDD-induced gene activation, regulators of small GTPases
of the Ras superfamily, UBX domain-containing proteins and the oncogenic
protein LYRIC. The results open up new directions for research on
the molecular mechanisms of dioxin action and toxicity