The process of cellular morphogenesis is highly conserved in eukaryotes and is dependent upon the function of proteins that are centrally involved in specification of the cell cycle. The human enhancer of invasion clone 10 (HEI10) protein was identified from a HeLa cell library based on its ability to promote yeast agar invasion and filamentation. Through two-hybrid screening, the mitotic cyclin B1 and an E2 ubiquitin-conjugating enzyme were isolated as HEI10-interacting proteins. Mutation of the HEI10 divergent RING finger motif (characteristic of E3 ubiquitin ligases) and Cdc2/cyclin binding and phosphorylation sites alter HEI10-dependent yeast phenotypes, including delay in G 2 /M transition. In vertebrates, the addition of HEI10 inhibits nuclear envelope breakdown and mitotic entry in Xenopus egg extracts. Mechanistically, HEI10 expression reduces cyclin B levels in cycling Xenopus eggs and reduces levels of the cyclin B ortholog Clb2p in yeast. HEI10 is itself a specific in vitro substrate of purified cyclin B/cdc2, with a TPVR motif as primary phosphorylation site. Finally, HEI10 is itself ubiquitinated in egg extracts and is also autoubiquitinated in vitro. These and other points lead to a model in which HEI10 defines a divergent class of E3 ubiquitin ligase, functioning in progression through G 2 /M.The spatial and temporal regulation of cell division is essential for development and normal cellular replacement in both unicellular and multicellular organisms. Cell cycle control and cell morphology are coordinated by complex signaling networks, the inappropriate perturbation of which can lead to either programmed cell death (apoptosis) or indefinite cell division cycles (cancer). The fact that many protein constituents of such pathways are conserved over great phylogenetic distances among eukaryotes emphasizes their importance. Since the 1980s, complementation studies in which human genes were identified based on the specific rescue of, or genetic interaction with, orthologous pathways in yeast have proven to be a fruitful means of gaining insight into mammalian growth controls. For example, the central cell cycle kinases CDC2 (32) and CDK2 (11) and the C, D, and E cyclins (15,24,53,57) were identified by complementation of yeast mutants.Analysis of yeast budding controls has been of particular interest as a model of cellular morphogenesis and has provided an interpretive framework for studies of signal transduction and morphological control processes in less experimentally amenable multicellular organisms (see, for example, reference 26). Bud emergence in vegetatively growing yeast is a complex process that depends on the rearrangement of the cytoskeleton throughout the different phases of the cell cycle (8, 56). The site of bud emergence is specified by signals that mark the location of a previous bud. In addition to the spatial regulation of budding, bud emergence is temporally synchronized with the different phases of the cell cycle and is sensitive to the environment. A coordinated response to change...

Human enhancer of invasion, clone 10 (HEI10) (CCNB1IP1) was first described as a RING-finger family ubiquitin ligase that regulates cell cycle by interacting with cyclin B and promoting its degradation. Subsequently, other studies suggested specific upregulation of HEI10 in metastatic melanoma and demonstrated direct interaction between HEI10 and the tumor suppressor Merlin, encoded by the neurofibromatosis 2 gene. These and other results led us to hypothesize that HEI10 also influences the processes of cell migration and metastasis. We here show that cells with depleted HEI10 both migrate more rapidly and invade more effectively than control cells. HEI10 depletion post-transcriptionally increases the expression of a group of promotility regulatory proteins including p130Cas, paxillin, Cdk1 and cyclin B2, but excluding Merlin. Among these, only inhibition of Cdk1/ cyclin B activity specifically reversed the motility and invasion of HEI10-depleted cells. Finally, HEI10 is abundantly transcribed in many human tissues, and particularly abundant in some tumor cell lines, suggesting that it may be commonly involved in coordinating cell cycle with cell migration and invasion.

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