Rabbit anti-Human eRF3/GSPT1 polyclonal antibody

Pomalidomide, a derivative of thalidomide, is an effective treatment for multiple myeloma. The drug exerts its effects through CRBN, a component of the E3 ubiquitin ligase complex CRL4(CRBN). To search for novel factors involved in the anti-cancer activity of pomalidomide, we performed a genome-wide shRNA library screen and identified 445 genes as those affecting pomalidomide sensitivity. Genes encoding components of the ubiquitin-proteasome pathway, such as subunits of the CRL4(CRBN) complex, the COP9 signalosome, and the 26S proteasome, were among the pomalidomide-affecting genes. Karyopherin beta 1 (KPNB1) was identified as a novel pomalidomide-affecting gene. KPNB1 was required for the nuclear import of CRBN and for the CRBN-directed, pomalidomide-dependent degradation of a clinically relevant substrate, the transcription factor Aiolos. By contrast, the cytoplasmic translation factor GSPT1 was degraded following treatment with the thalidomide derivative CC-885 only when CRBN was present in the cytoplasm, indicating that subcellular distribution of CRBN is critical for the efficacy of thalidomide-based medications.

Background: The termination of protein synthesis in eukaryotes involves at least two polypeptide release factors (eRFs), eRF1 and eRF3. In mammals two genes encoding eRF3 structural homologues were identified and named GSPT1 and GSPT2. Results: In the present study, we demonstrate that mouse mGSPT2 but not mGSPT1 could functionally substitute the essential yeast gene SUP35 . However, we show that the complementation property of mGSPT1 protein is modified when NH2 -tagged by GST. Since mGSPT1 and mGSPT2 differ mainly in their N-terminal regions, we developed a series of N-terminal deleted constructs and tested them for complementation in yeast. We found that at least amino acids spanning 84-120 of mGSPT1 prevent the complementation of sup35 mutation. The fact that chimeras between mGSPT1, mGSPT2 and yeast Sup35 complement the disruption of the SUP35 gene indicates that the N-terminal region of mGSPT1 is not sufficient by itself to prevent complementation. Complementation of the mutant with a double disruption of SUP35 and SUP45 genes is obtained when mGSPT2 and human eRF1 are co-expressed but not by co-expression of mGSPT1 and human eRF1. Conclusions: Our results strongly suggest that the two proteins (mGSPT1 and mGSPT2) are different. We hypothesize that the full length mGSPT1 does not have the properties expected for eRF3.