Identification of DRG family regulatory proteins (DFRPs): specific regulation of DRG1 and DRG2

Abstract

DRG1 and DRG2 comprise a highly conserved subfamily of GTP-binding proteins and are thought to act as critical regulators of cell growth. Their abnormal expressions may trigger cell transformation or cell cycle arrest. Our aim is to clarify their physiological functions and regulatory mechanisms. Here we report identification of novel proteins, D RG f amily r egulatory p rotein (DFRP) 1 and DFRP2, which regulate expression of DRG proteins through specific binding. In transient transfection experiments, DFRP1 specifically binds DRG1, and DFRP2 preferentially binds DRG2. DFRPs provide stability to the target DRG proteins through physical association, possibly by blocking the poly-ubiquitination that would precede proteolysis of DRG proteins. DFRPs are highly conserved in eucaryotes, and the expression patterns of dfrp1 and drg1 transcripts in Xenopus embryos and tissues are similar, indicating that these genes work cooperatively in various types of eukaryotic cells. Immunofluorescence experiments have revealed that the interaction between DRG1 and DFRP1 may occur in the cytoplasm. We generated dfrp1 -knockout cells and found that endogenous expression of DRG1 is regulated by DFRP1, confirming that DFRP1 is a specific up-regulator of DRG1 in vivo . On the basis of these results, we propose that DRG1 and DRG2 are regulated differently despite their structural similarities.

Characterization of ZC3H15 as a potential TRAF-2-interacting protein implicated in the NFκB pathway and overexpressed in AML

“…It was shown that DFRP1 binds to DRG1 specifically thereby blocking the DRG1 polyubiquitination and proteolysis and thus upregulating the level of DRG1. Immunofluorescence microscopy demonstrated that DFRP1 and DRG1 co-localized throughout the whole cytosol without associating with the endoplasmic reticulum, Golgi or mitochondria (3). In summary, these data suggest that ZC3H15 (DFRP1) is part of one or several signaling pathway(s) that are important for cell proliferation.…”

“…ZC3H15's synonymous name, likely ortholog of mouse immediate early response erythropoietin 4 (LEREPO4) gene (2), suggests that it was swiftly induced by erythropoietin as a growth factor. Another name, DRG family regulatory protein 1 (DFRP1) (3) indicates that it regulates developmentally regulated GTP-binding protein 1 (DRG1) suggesting a role in cellular signaling. We initially found ZC3H15 (LEREPO4) as a potential HIV-dependency factor (4).…”

Expression Patterns ofArabidopsis DRGGenes: Promoter‐GUS Fusions, Quantitative Real‐Time PCR, and Patterns of Protein Accumulation in Response to Environmental Stresses

“…In this case, however, protein levels were constant, whereas mRNA levels were more abundant in growing buds than in dormant buds. DRG1 and DRG2 from Xenopus, human, and mouse are susceptible to polyubiquitination and degradation by the 26S proteosome pathway (Ishikawa et al 2005). Each DRG protein is stabilized through an interaction with a specific DRG family regulatory protein (DFRP).…”

Saccharomyces cerevisiae Rbg1 Protein and Its Binding Partner Gir2 Interact on Polyribosomes with Gcn1

“…In fact, the mammalian Rbg proteins interact with protein orthologs we identified in the present study, with some interesting differences: mammalian DRG1 (ortholog to yeast Rbg1) binds to DFRP1 (Tma46), and DRG2 (Rbg2) binds to DFRP2 (Gir2) (24). These DRG proteins are susceptible to degradation through the ubiquitin-mediated pathway, and their degradation is prevented by their interaction with DFRP proteins.…”