Specificity, location and function of βTrCP isoforms and their splice variants

SCF beta TrCP is the ubiquitin ligase for a wide variety of substrates and functions in many cellular processes. beta TrCP, the substrate binding factor of the SCF complex, has two isoforms, produced from different genes, and several splice variants. Despite a certain level of redundancy, knock-out studies show different phenotypes indicating different preferential substrates for the two isoforms. However, until now functional differences between beta TrCP1 and 2 were not studied at the endogenous protein level. We generated isoform-specific antibodies against beta TrCP to characterise endogenous beta TrCP isoforms and splice variants. We show that endogenous beta TrCP1 and 2 localise to both nucleus and cytosol. Interestingly, we find that one splice variant of beta TrCP2 localises exclusively to the nucleus and another only to the cytosol. In addition, we show that the substrate binding domain of beta TrCP is the dominant localisation determinant. (C) 2010 Elsevier Inc. All rights reserved.