On the other hand, the two tryptophan residues located at amino acids 288 and 290 display a synergic nucleolar localization effect [11] additive to the contribution of the canonical NLS sequences positioned at 152–157 and 190–197 [33]. Different Staurosporine purchase mutations generate a de novo C-terminal NES leading to a complete shift of the equilibrium toward the cytoplasmic accumulation. At the same time, the inhibition tests in the presence of leptomycin B confirm that the

situation remains highly dynamic, since the NPMc+ is relocated to the nucleus in less than 1 h. These observations suggest that NPMc+ is not sequestered in the cytoplasm, that the apparent lack of relocalization is due to unequal rates of translocation in the two directions, and that a modification between the relative speed of export and import might re-establish a preferential nuclear accumulation. It has been recently reported that CRM1 overexpression modifies this equilibrium and correlates with metastasis and poor prognosis in different human cancers [34]. However, despite Metformin cost some positive pre-clinical indications [35] and [36], this transporter controls the shuttling of too many essential proteins to be considered an ideal therapeutic target. As an alternative possibility, the equilibrium between

the two opposite fluxes could be modified by acting on the strength of the import/export motifs, as it happens in some pathological conditions [37]. The therapeutic potential of tuning the protein delivery to suitable sub-cellular compartments by means of intrabodies have been recently reviewed [21] and [38]. Conventional IgGs do not fold correctly in the reducing cytoplasmic milieu but recombinant antibody fragments with simpler structures can reach their functional conformation despite the unfavorable redox conditions. In basic research, the effect of the rapid removal of cytoplasmic proteins has been evaluated by using single-domain

antibodies that can trap GFP-tagged proteins and deliver them to ubiquitin-dependent Protein tyrosine phosphatase degradation [39]. However, protein sub-cellular re-localization is not a straightforward application since artificially introduced sub-cellular localization sequences clash with native and discording signal sequences [40], a condition that can result in unpredictable protein distribution inside the cell [37]. Furthermore, physiological NES and NLS have apparently evolved as “weak” signals, whereas pathological motifs can be extremely more effective. In this perspective, it would be crucial to have models to predict the effect of coexisting signal sequences of different strength and driving to opposite directions.