Identification of Ubiquitin Ligase Activity of RBCK1 and Its Inhibition by Splice Variant RBCK2 and Protein Kinase C

Department of Structural Molecular Biology, The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan.
Journal of Biological Chemistry (Impact Factor: 4.57). 05/2008; 283(17):11575-85. DOI: 10.1074/jbc.M706961200
Source: PubMed


We previously identified a RING-IBR protein, RBCK1, as a protein kinase C (PKC) β- and ζ-interacting protein, and its splice
variant, RBCK2, lacking the C-terminal half including the RING-IBR domain. RBCK1 has been shown to function as a transcriptional
activator whose nuclear translocation is prevented by interaction with the cytoplasmic RBCK2. We here demonstrate that RBCK1,
like many other RING proteins, also possesses a ubiquitin ligase (E3) activity and that its E3 activity is inhibited by interaction
with RBCK2. Moreover, RBCK1 has been found to undergo efficient phosphorylation by PKCβ. The phosphorylated RBCK1 shows no
self-ubiquitination activity in vitro. Overexpression of PKCβ leads to significant increases in the amounts of intracellular RBCK1, presumably suppressing the
proteasomal degradation of RBCK1 through self-ubiquitination, whereas coexpression with PKCα, PKCϵ, and PKCζ shows no or little
effect on the intracellular amount of RBCK1. Taken together, the E3 activity of RBCK1 is controlled by two distinct manners,
interaction with RBCK2 and phosphorylation by PKCβ. It is possible that other RING proteins, such as Parkin, BRCA1, and RNF8,
having the E3 activity, are also down-regulated by interaction with their RING-lacking splice variants and/or phosphorylation
by protein kinases.

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    • "Alternative splicing events on intrinsically disordered protein regions could regulate interactions of PARK2 isoforms with specific cellular targets. In addition, PARK2 isoforms generated by different alternative splice transcripts could interact with each other mutually regulating their functions, as it has been reported for RBCK1, a protein with IBR and E3 ubiquitin ligase domains, whose migration in the nucleus is inhibited by interaction with RBCK2, an isoform lacking IBR domain [36]. "
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