Biomedical subjects

O Ullrich

Publications and source records attributed to O Ullrich.

39 records · Page 3Linked to original sources

PubMed1991

Biosynthesis and secretion of an osteopontin-related 20-kDa polypeptide in the Madin-Darby canine kidney cell line.

We describe a 20-kDa phosphorylated polypeptide, which is secreted constitutively at the apical surface of the kidney-derived Madin-Darby canine kidney cell line. Using polyclonal antibodies raised against this protein, we show that it is generated from a 60-kDa O-glycosylated, sulfated, and phosphorylated precursor protein by an intracellular proteolytic maturation step, which is pH-sensitive. Amino acid sequence analysis of the 20-kDa secreted polypeptide demonstrated that it displays 70% identity with the carboxyl-terminal amino acids of human osteopontin. The amino-terminal amino acid of the 20-kDa polypeptide corresponds to amino acid 213 of human osteopontin. Thrombin has been shown to cleave rat osteopontin in vivo and in vitro at amino acid 153, yielding two fragments of 28 and 26 kDa. A similar cleavage product can be detected by thrombin treatment of the 60-kDa precursor, suggesting that the precursor is identical or closely related to osteopontin. In the rat nephron, the protein has been localized along the luminal surfaces of the proximal and distal tubule and the collecting duct cells. These results show that in the kidney-derived cell line Madin-Darby canine kidney osteopontin or a closely related protein is proteolytically processed to a 20-kDa polypeptide, raising the possibility that diverse functions of osteopontin in various tissues might be attributed to specific processing to distinct polypeptides.

Amino Acid Sequence↗

PubMedDate not supplied

Apical transport of osteopontin is independent of N-glycosylation and sialylation.

Studies of how epithelial surface polarity into apical and basolateral domains is generated and maintained have proposed that carbohydrate modifications serve as apical targeting signals for proteins by interacting with lectin sorters. However, the experimental evidence in support of N-glycans, O-glycans and sialic acids mediating apical transport is still very controversial. This could be partly due to the fact that in most studies exogenously expressed proteins were analysed. One has, therefore, examined the role of carbohydrate moieties in apical targeting of the endogenous secretory protein osteopontin in MDCK cells. It was found, however, that sorting of osteopontin does not require N-glycosylation of the protein itself nor that of other factors involved in the sorting process. Incubation of cells with the inhibitor of O-glycosylation benzyl-alpha-GaINAc reduced the molecular weight of osteopontin by blocking sialic acid addition to O-glycans. Interestingly, also impairment of sialylation had no effect on polar secretion of the protein. Thus, the results show that both N-glycans and sialic acids are not essential sorting signals, suggesting that inner core carbohydrates and/or a proteinaceous signal mediate apical targeting of osteopontin.

Acetylgalactosamine↗

PubMedDate not supplied

LPS-induced protein oxidation and proteolysis in BV-2 microglial cells.

Exposure of proteins to oxidants leads to increased oxidation followed by preferential degradation by the proteasomal system. The role of the biological oxidant production in microglial BV-2 cells in the oxidation and turnover of endogenous proteins was measured. It could be demonstrated, that BV-2 cells are relatively resistant to fluxes of oxidants, but nevertheless protein oxidation occurs due to activation by LPS. This protein oxidation is followed by an enhanced degradation of endogenous proteins. Using PBN, a free radical scavenger and antioxidant, we could demonstrate the involvement of free radicals in the increased proteolysis in BV-2 cells after LPS-treatment. A slight but significant up-regulation of the proteasomal system after LPS activation takes place, indicating the importance of his proteolytic system in the maintenance of the protein pool of microglial cells.

Animals↗