RNF138 or NARF is a Cell Cycle Regulated E3 Ligase that Poly-ubiquitinates G2E3 - Abstract
G2E3 is a G2/M-specific gene that is down-regulated in response to DNA damage. It is highly regulated at both the transcriptional and post-translational levels. It plays a critical role in early embryonic development, as murine G2E3-deficient blastula undergoes a massive apoptosis. To identify proteins interacting with G2E3 a yeast two-hybrid was conducted, which revealed eight putative G2E3-binding proteins including two ubiquitin ligases (RNF138/NARF, DZIP3/hRUL138), a proteasomal subunit (PSMB4), and one cell cycle regulatory molecule (INCA1). We examined a possible functional interaction between G2E3 and the putative oncogene RNF138/NARF, demonstrating that RNF138/NARF has a subcellular localization and cell cycle regulated expression pattern similar to that of G2E3. The regions of each protein necessary for interaction were mapped to the C-terminus of RNF138/NARF and the N-terminus of G2E3. Furthermore, we demonstrated that RNF138/NARF catalyzes the poly-ubiquitination of G2E3 in vitro and in vivo. Ubiquitination of G2E3 by RNF138/NARF provides another mechanism for the regulation of this protein. Because depletion of either G2E3 or RNF138/NARF causes cellular apoptosis, this functional interaction may be important in the regulation of cell death.