Abstract
Steroid hormone receptors are ligand-stimulated transcription factors that modulate gene transcription by recruiting coregulators to gene promoters. Subcellular localization and dynamic movements of transcription factors have been shown to be one of the major means of regulating their transcriptional activity. In the present report we describe the subcellular localization and the dynamics of intracellular trafficking of steroid receptor coactivator 1 (SRC-1). After its synthesis in the cytoplasm, SRC-1 is imported into the nucleus, where it activates transcription and is subsequently exported back to the cytoplasm. In both the nucleus and cytoplasm, SRC-1 is localized in speckles. The characterization of SRC-1 nuclear localization sequence reveals that it is a classic bipartite signal localized in the N-terminal region of the protein, between amino acids 18 and 36. This sequence is highly conserved within the other members of the p160 family. Additionally, SRC-1 nuclear export is inhibited by leptomycin B. The region involved in its nuclear export is localized between amino acids 990 and 1038. It is an unusually large domain differing from the classic leucine-rich NES sequences. Thus SRC-1 nuclear export involves either an alternate type of NES or is dependent on the interaction of SRC-1 with a protein, which is exported through the crm1/exportin pathway. Overall, the intracellular trafficking of SRC-1 might be a mechanism to regulate the termination of hormone action, the interaction with other signaling pathways in the cytoplasm and its degradation.
Highlights
Ʈ Present address: CNRS UPR9079, Oncogenese, differenciation et transduction du signal, Institut Andre Lwoff, 7 rue Guy Moquet, 94800 Villejuif, France
steroid receptor coactivator 1 (SRC-1) Is Localized in Both the Cytoplasm and the Nucleus— We transfected COS-7 cells with an expression vector encoding SRC-1 to examine its subcellular distribution
Immunocytochemical detection (40 h post-transfection) using a specific antiSRC-1 antibody showed the protein to be present in both the cytoplasm and the nucleus in about 50% of cells (Fig. 1, a– c)
Summary
Ʈ Present address: CNRS UPR9079, Oncogenese, differenciation et transduction du signal, Institut Andre Lwoff, 7 rue Guy Moquet, 94800 Villejuif, France. SRC-1 Is Localized in Both the Cytoplasm and the Nucleus— We transfected COS-7 cells with an expression vector encoding SRC-1 to examine its subcellular distribution. Immunocytochemical detection (40 h post-transfection) using a specific antiSRC-1 antibody showed the protein to be present in both the cytoplasm and the nucleus in about 50% of cells (Fig. 1, a– c).
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