Subcellular Localization and Mechanisms of Nucleocytoplasmic Trafficking of Steroid Receptor Coactivator-1

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.

Redundant enhancement of mouse constitutive androstane receptor transactivation by p160 coactivator family members

“…In contrast, exogenously expressed GFPSRC-2 and GFPSRC-3 were localized exclusively in the nucleus, both diffusely and in discrete round granules. Our observation of SRC-1 localization is consistent with the presence of exogenously expressed SRC-1 detected by immuno-fluorescence in both cytoplasm and nucleus as speckles in all cell types [32]. Localization of transcriptional regulators in nuclear speckles has been described before, but the presence of similar structures in the cytoplasm is rarely observed [33,37].…”

“…SRC-1 has been reported to be present in the nucleus [28,29,30], in the cytoplasm [31] or in both compartments [32]. Similar divergent data have been described for SRC-3, ranging from cytoplasmic to diffuse nucleoplasmic or discrete intranuclear foci [33,34].…”

Visualization of Glucocorticoid Receptor and Mineralocorticoid Receptor Interactions in Living Cells with GFP-Based Fluorescence Resonance Energy Transfer

“…The explanation for this opposite effect and the role of heterodimerization is still ambiguous, and the differences in transfection conditions, cell types, reporters, or promoters must be taken into consideration. Transcriptional cofactors are also another very important player to consider when evaluating the transcription activities of the GR and MR (Amazit et al, 2003), which were not discussed in the previous studies reporting heterodimer of GR and MR.…”

Effect of nuclear export inhibition on estrogen receptor regulation in breast cancer cells

“…It could be that steroid receptors interact with Crm1 thanks to a co-regulator behaving as an adapter. In this context, it has been recently reported that steroid receptor co-activator-1 (a member of the p160 family) is exported from cell nuclei by a LMB-sensitive process (Amazit et al 2003).…”