Covalent modification of all members of human cullin family proteins by NEDD8

Recently we found that NEDD8, a ubiquitin-like protein, was linked covalent ly to human cullin-4A (abbreviated Cul-4A) by a new ubiquitin-related pathw ay that is analogous to but distinct from the ligating system for SUMO1, an other ubiquitin-like protein. However, it remained unknown whether the othe r five members of the family of human cullin/Cdc53 proteins are modified by NEDD8, Here we report that all Hs-Cul family proteins, such as Cul-1, Cul- 2, Cul-3, Cul-4B, and Cul-5, in addition to Cul-4A, were modified by covale nt attachment of NEDD8 in rabbit reticulocyte lysates, Moreover, by compreh ensive Northern-blot analyses, we examined multiple tissue distributions of the messages for all Cul-family proteins, NEDD8, and the NEDD8-ligating sy stem consisting of APP-BP1/hUba3, and hUbc12, which function as E1- and E2- like enzymes, respectively, The expressions of Cul-1, Cul-2, and Cul-3 rese mbled each other and were apparently correlated to those of NEDD8 and the N EDD8-ligating system in various human cells and tissues. However, the mRNA levels of Cul-4A, Cul-4B, and Cul-5 differed considerably from each other a s well as from other Cul-family proteins. The enhanced expression of all Cu l-family proteins except Cul-5 was observed in a variety of tumor cell line s.