Identification of polyubiquitin binding proteins involved in NF-kappaB signaling using protein arrays.

Attachment of ubiquitin to proteins represents a central mechanism for the regulation of protein metabolism and function. In the NF-kappaB pathway, binding of NEMO to polyubiquitinated substrates initiates the pathway in response to cellular stimuli. Other polyubiquitin binding proteins can antagonize this pathway by competing with NEMO for polyubiquitin. We have used protein arrays to identify polyubiquitin binding proteins that regulate NF-kappaB activity. Using polyubiquitin as bait, protein arrays were screened and polyubiquitin binders identified. Novel polyubiquitin binders AWP1, CALCOCO2, N4BP1, RIO3, TEX27, TTC3, UBFD1 and ZNF313 were identified using this approach, while known NF-kappaB regulators including NEMO, A20, ABIN-1, ABIN-2, optineurin and p62 were also identified. Overexpressed AWP1 and RIO3 repressed NF-kappaB activity in a manner similar to optineurin, while siRNAs directed against AWP1 and RIO3 also reduced NF-kappaB activity. TNFalpha-dependent degradation of IkappaBalpha was also suppressed by overexpression of AWP1 and RIO3, possibly due to the polyubiquitin binding activity of these proteins. Protein array screening using polyubiquitin enabled rapid identification of many known and novel polyubiquitin binding proteins and the identification of novel NF-kappaB regulators.