[A new human cellular protein AUP1. I. In vitro interaction of AUP1 with adenoviral proteins E4ORF3 and E1A]

The 11-kDa product of adenovirus early region 4 (E4) open reading frame (ORF) 3 participates in many processes occurring in infected cell, including post-transcriptional steps in late viral gene expression and viral DNA synthesis. In addition, E4ORF3 from adenovirus type 5 (Ad5) displays the features of a viral oncoprotein. It initiates focal transformation of primary rat cells in cooperation with Ad5 El genes and confers multiple additional transformed properties on E1-expressing cells. Biochemical details of E4ORF3 activities in these processes are not well understood. A large body of evidence indicates that its lytic and transforming functions are mediated by physical interactions with viral and cellular components involved in DNA transcription and repair, as well as by host cell factors that regulate the integrity of nuclear multiprotein complexes known as PML oncogenic domains (PODs). In this study we have employed the two-hybrid screen in yeast to isolate human cDNAs encoding for E4ORF3-interacting proteins. Among 15 positive clones five cDNAs encode for a cellular protein called AUP1. In vitro-binding assays demonstrated that AUP1 fused to glutathione S-transferase (GST) specifically binds to E4ORF3 from Ad5, Ad9 and Ad40 generated in a coupled transcription-translation system, whereas no interactions was observed with ORF3 from Ad12. Interestingly, GST-AUP1 interacted also specifically with in vitro translated Ad5 E1A proteins. Regions involved in the Ad5 E4ORF3/AUP1 interaction in vitro map to the central part of E4 protein and the carboxy-terminal region of AUP1, while E1A binds to an amino-terminal segment of the cell protein. Taken together, these studies indicate that AUP1 may represent a cellular target of both adenovirus E4ORF3 and E1A proteins. Additional studies are currently under way to confirm the significance of these interactions in living cells in vivo.

[A new human cellular protein AUP1. III. The intracellular localization of AUP1 protein in different human and rat cell lines]

Previously, we cloned a full-length cDNA of human Aup1 and showed that AUP1 may represent a new cellular target for the two adenovirus oncoproteins, E1A Ad5 and E4ORF3. In this study, we generated a polyclonal anti-AUP1 antibody and examined the subcellular localization of AUP1 in MCF7 cells, HeLa cells, H1299 cells, 293 cells, BRK1 cells and transfectants expressing adenoviruse E1 genes. Double staining of AUP1 and various markers for cytoplasmic structures showed that the pattern of AUP1 distribution in the cytoplasm was puctuate and diffuse and without any colocalization with Golgi apparatus or endoplasmic reticulum. Additional studies with ectopically expressed AUP1, fused with red fluorescent protein (RFP) in H1299 and McG7 human cell lines and BRK1 rat cell line, showed cytoplasmic localization of RFP-AUP1. Western blot analysis revealed that AUP1 was expressed at similar levels in all tested cell lines and had the same molecular weight as the rat protein (45 kDa). Taken together, these results suggest that AUP1 is a cytoplasmic protein that is expressed in all cell lines we examined.

Pulmonary surfactant proteins A and D enhance neutrophil uptake of bacteria

The collectins are a class of collagenous lectin proteins present in serum and pulmonary secretions [pulmonary surfactant protein (SP) A and SP-D] that are believed to participate in innate immune responses to various pathogens. With the use of flow cytometric and fluorescent-microscopic assays, SP-A and SP-D were shown to increase calcium-dependent neutrophil uptake of Escherichia coli, Streptococcus pneumoniae, and Staphylococcus aureus. Evidence is provided that the collectins enhanced bacterial uptake through a mechanism that involved both bacterial aggregation and direct actions on neutrophils. The degree of multimerization of SP-D preparations was a critical determinant of both aggregating activity and potency in enhancing bacterial uptake. The mechanisms of opsonizing activity of SP-D and SP-A differed in important respects from those of opsonizing antibodies. These results provide the first evidence that surfactant collectins may promote neutrophil-mediated clearance of bacteria in the lung independently of opsonizing antibody.