Eukaryotic DING Proteins Are Endogenous: An Immunohistological Study in Mouse Tissues

Abstract

BackgroundDING proteins encompass an intriguing protein family first characterized by their conserved N-terminal sequences. Some of these proteins seem to have key roles in various human diseases, e.g., rheumatoid arthritis, atherosclerosis, HIV suppression. Although this protein family seems to be ubiquitous in eukaryotes, their genes are consistently lacking from genomic databases. Such a lack has considerably hampered functional studies and has fostered therefore the hypothesis that DING proteins isolated from eukaryotes were in fact prokaryotic contaminants.Principal FindingsIn the framework of our study, we have performed a comprehensive immunological detection of DING proteins in mice. We demonstrate that DING proteins are present in all tissues tested as isoforms of various molecular weights (MWs). Their intracellular localization is tissue-dependant, being exclusively nuclear in neurons, but cytoplasmic and nuclear in other tissues. We also provide evidence that germ-free mouse plasma contains as much DING protein as wild-type.SignificanceHence, data herein provide a valuable basis for future investigations aimed at eukaryotic DING proteins, revealing that these proteins seem ubiquitous in mouse tissue. Our results strongly suggest that mouse DING proteins are endogenous. Moreover, the determination in this study of the precise cellular localization of DING proteins constitute a precious evidence to understand their molecular involvements in their related human diseases.

Structural insights andab initiosequencing within the DING proteins family

“…DING proteins were observed in all tested tissues, namely brain, skin, heart, aorta, lung and liver, suggesting that these proteins are widely expressed within the organism (Collombet et al, 2010). A western blot study on these samples also confirms previous assumptions, stemming from the partial (a) Close view of a ball-and-stick representation of the R374 region in the HPBP structure at 1.9 Å resolution.…”

“…The 2f obs À f calc electronic density map is contoured at 1.5. gene found in Leishmania major genome and western blot studies on plant tissues (Perera et al, 2008), suggesting that DING proteins exists also as high-molecular-weight proteins (HMW-DING). Indeed, if most of the characterized DING proteins are 38 kDa proteins, our western blot study shows that several HMW-DINGs exists, such as the 140 kDa, the 71 kDa, the 62 kDa and the 52 kDa DING (Collombet et al, 2010). The presence of several isoforms of DING proteins might be linked with different biological activities.…”

Human-Phosphate-Binding-Protein inhibits HIV-1 gene transcription and replication

“…The ubiquitous presence in eukaryotes of proteins structurally and functionally related to bacterial virulence factors is intriguing, as is the absence of eukaryotic genes encoding DING proteins in databases. However, theoretical arguments together with experimental evidences supported an eukaryotic origin for DING proteins [ 29 , 30 ]. A member of the DING family proteins, HPBP, was serendipitously discovered in human plasma while performing structural studies on another target, the HDL-associated human paraoxonase hPON1 [ 31 - 33 ].…”

“…Later, the ab initio sequencing of HPBP by tandem use of mass spectrometry and X-ray crystallography confirmed that its gene was missing from the sequenced human genome [ 38 ]. Immunohistochemistry studies performed in mouse tissues demonstrate that DING proteins are present in most of tissues, spanning from neurons to muscle cells and their cellular localization is largely variable, being exclusively nuclear in neurons, or nuclear and cytoplasmic in muscle cells [ 30 ]. Altogether, these localizations are consistent with the biological function that was associated to these proteins, especially the regulation/alteration of cell cycle.…”

The Level of DING Proteins Is Increased in HIV-Infected Patients: In Vitro and In Vivo Studies

“…Serum concentration of DING proteins was measured by in-house ELISA using rabbit polyclonal antibodies generated against HPBP. Details of the purification methods and antibody production have been previously reported [12] , [24] . Because of the high sequence conservation between DING proteins, anti-HPBP antibodies are able to recognize several representatives of the DING family.…”