A small-scale survey identifies selective and quantitative nucleo-cytoplasmic shuttling of a subset of CREM transcription factors.
Elucidating dynamic aspects of intracellular localization of proteins is essential to decipher their functional interaction networks. Although transcription factors lacking a detectable cytoplasmic fraction have been generally considered compartmentalized in the nucleus, some were found to shuttle into the cytoplasm, suggesting functional interactions therein. To further investigate how common, specific and quantitative is this traffic, we have employed the heterokaryon assay for a small-scale survey of nuclear factors not previously tested for their nucleo-cytoplasmic motion. We show that a subset of cAMP response element (CRE) binding proteins of the CREM type shuttles within a biologically meaningful time frame, revealing a continuous flow into the cytoplasm that persists during signaling. Their dynamic behavior, not involving the classical Exportin-1 pathway, could be ascribed to C-terminal sequences, containing, in addition to the bZIP domain and the NLS, a nuclear export activity and an inhibitory activity at an adjacent site. Other proteins examined in this study either did not shuttle significantly or, like CREB and distinct CREM isoforms, shuttled with markedly delayed kinetics, denoting considerable selectivity of this traffic. These findings raise the possibility that events associated with bi-directional transport and periodic transit through the cytoplasm may modulate activities of select nuclear transcription factors.
DIBIT-San Raffaele Scientific Institute, Via Olgettina 58, 20132 Milan, Italy.
Angelia
A
Fenaroli
Milos
M
Vujanac
Dario
D
De Cesare
Vincenzo
V
Zimarino
D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000818:Animals; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D006224:Cricetinae; D051786:Cyclic AMP Response Element Modulator; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D028884:Karyopherins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D051379:Mice; D041681:NIH 3T3 Cells; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000235:genetics; D018160:Receptors, Cytoplasmic and Nuclear; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D000097606:Exportin 1 Protein
D051786:Cyclic AMP Response Element Modulator; D004268:DNA-Binding Proteins; D005231:Fatty Acids, Unsaturated; D028884:Karyopherins; D020033:Protein Isoforms; D018160:Receptors, Cytoplasmic and Nuclear; D012097:Repressor Proteins; D014157:Transcription Factors; D000097606:Exportin 1 Protein; C038753:leptomycin B