The NBPF genes are members of a gene family that underwent a remarkable increase in their copy number during recent primate evolution. The NBPF proteins contain 5 to 40 copies of a domain known as the NBPF repeat or DUF1220. Very little is known about the function of these domains or about the NBPF proteins. We performed a yeast two-hybrid screening with the aminoterminal domain of NBPF11 and found that Chibby, a documented repressor of Wnt signaling, interacts with multiple NBPF proteins. More specifically, a coiled-coil region in the NBPF proteins interacts with the coiled-coil domain in the carboxyterminal region of Chibby. Nonetheless, this interaction did not influence the repressor function of Chibby in a TOPFLASH reporter assay. Using Chibby as bait in a new yeast two-hybrid screening, we identified clusterin as a binding protein. Chibby and clusterin were co-immunoprecipitated with NBPF1, suggesting the formation of a tri-molecular complex. Although we have not pinpointed the role of these mutual interactions, the possible formation of a macromolecular complex of three candidate tumor suppressor proteins, including the enigmatic NBPF1, points at important functional implications.
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