Essential requirement for RING finger E3 ubiquitin ligase Hakai in early embryonic development of Drosophila

Abstract

Hakai is a RING finger type E3 ubiquitin ligase that is highly conserved in metazoans. Mammalian Hakai was shown to bind and ubiquitinate the intracellular domain of E-cadherin, and this activity is implicated in down-regulation of E-cadherin during v-Src-induced cellular transformation. To evaluate this model in vivo, we studied the function of the Drosophila homologue of Hakai. In cultured S2 cells, Drosophila Hakai and E-cadherin (Shotgun) formed a complex in a way distinct from the interaction described for mammalian counterparts. Hakai null mutants died during larval stages but this lethality could be offset by a HA-tagged Hakai construct. While zygotic Hakai function was dispensable for cell proliferation and differentiation in the wing disc epithelium, maternal Hakai mutants showed a variety of defects in epithelial integrity, including stochastic loss of E-cadherin expression and reduction of aPKC; defects in cell specification and cell migration were also observed. No increase of E-cadherin, however, was observed. Regulation of multiple target proteins under control of Hakai is, therefore, essential for early embryonic morphogenesis in Drosophila.

Identification of factors required for m6A mRNA methylation in Arabidopsis reveals a role for the conserved E3 ubiquitin ligase HAKAI

“…More recently, it has also been implicated with influencing RNA–protein interactions in animal systems (Fujita et al ., 2002; Figueroa et al ., 2009) and has been reported in association with m 6 A writers (Horiuchi et al ., 2013), but a role in m 6 A writing has not been proposed until now. Although believed to act on E‐cadherin complex at the plasma membrane, human and D. melanogaster HAKAIs are localized predominantly in the nucleus and in lower amounts at the plasma membrane and in the cytoplasm (Figueroa et al ., 2009; Kaido et al ., 2009). Arabidopsis HAKAI‐mCherry resides mainly in the nucleus (Fig.…”

Ontogeny of small RNA in the regulation of mammalian brain development

“…Cbll1 is a RING finger type E3 ubiquitin ligase and an important regulator of cell proliferation [48]. In Drosophila, Cbll1 is required for proper function of cell surface proteins and for endoderm and mesoderm morphogenesis [49]. Consistent with the increase of miR-212 expression between E12 and E19, Cbll1 function is demonstrated to be most vital in the early stages of embryogenesis, with its contribution declining in later stages [49].…”

Identification of Wilms' Tumor 1-associating Protein Complex and Its Role in Alternative Splicing and the Cell Cycle

“…In addition to its role in cell-cell contact, Hakai has recently been shown to promote cell proliferation in Drosophila embryo (28) and mammalian cells and to enhance the RNAbinding ability of polypyrimidine tract-binding protein-associ- ated splicing factor (29). Hakai contains a RING finger (aa 106 -148) and a phosphotyrosine-binding domain (aa 148 -206) called the Hakai Tyr(P)-binding (HYB) domain, as characterized by biochemical and crystal structural analyses (30), and a proline-rich domain in the C terminus.…”