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Stat5 and Sp1 Regulate Transcription of the Cyclin D2 Gene in Response to IL-21

The IL-2R promotes rapid expansion of activated T cells through signals mediated by the adaptor protein Shc and the transcription factor Stat5. The mechanisms that engage the cell cycle are not well defined. We report on the transcriptional regulation of the cell cycle gene cyclin D2 by the IL-2R. IL-2-responsive induction of a luciferase reporter gene containing 1624 bp of the cyclin D2 promoter/enhancer was studied in the murine CD8+ T cell line CTLL2. Reporter gene deletional analysis and EMSAs indicate an IL-2-regulated enhancer element flanks nucleotide −1204 and binds a complex of at least three proteins. The enhancer element is bound constitutively by Sp1 and an unknown factor(s) and inducibly by Stat5 in response to IL-2. The Stat5 binding site was essential for IL-2-mediated reporter gene activity, and maximum induction required the adjacent Sp1 binding site. Receptor mutagenesis studies in the pro-B cell line BA/FG (a derivative of the BA/F3 cell line) demonstrated a correlation between Stat5 activity and cyclin D2 mRNA levels when the Stat5 signal was isolated, disrupted, and then rescued. Further, a dominant-negative form of Stat5 lacking the trans-activation domain inhibited induction of cyclin D2 mRNA. We propose that the IL-2R regulates the cyclin D2 gene in part through formation of an enhancer complex containing Stat5 and Sp1.