RESUMO
Most antigenic peptides presented by MHC class I molecules result from the degradation of intracellular proteins by the proteasome. In lymphoid tissues and cells exposed to IFNγ, the standard proteasome is replaced by the immunoproteasome, in which all of the standard catalytic subunits ß1, ß2, and ß5 are replaced by their inducible counterparts ß1i, ß2i, and ß5i, which have different cleavage specificities. The immunoproteasome thereby shapes the repertoire of antigenic peptides. The existence of additional forms of proteasomes bearing a mixed assortment of standard and inducible catalytic subunits has been suggested. Using a new set of unique subunit-specific antibodies, we have now isolated, quantified, and characterized human proteasomes that are intermediate between the standard proteasome and the immunoproteasome. They contain only one (ß5i) or two (ß1i and ß5i) of the three inducible catalytic subunits of the immunoproteasome. These intermediate proteasomes represent between one-third and one-half of the proteasome content of human liver, colon, small intestine, and kidney. They are also present in human tumor cells and dendritic cells. We identified two tumor antigens of clinical interest that are processed exclusively either by intermediate proteasomes ß5i (MAGE-A3(271-279)) or by intermediate proteasomes ß1i-ß5i (MAGE-A10(254-262)). The existence of these intermediate proteasomes broadens the repertoire of antigens presented to CD8 T cells and implies that the antigens presented by a given cell depend on their proteasome content.
Assuntos
Apresentação de Antígeno , Antígenos de Histocompatibilidade Classe I/metabolismo , Complexo de Endopeptidases do Proteassoma/classificação , Complexo de Endopeptidases do Proteassoma/metabolismo , Sequência de Aminoácidos , Animais , Antígenos de Neoplasias/genética , Antígenos de Neoplasias/metabolismo , Linhagem Celular Tumoral , Humanos , Camundongos , Camundongos Knockout , Dados de Sequência Molecular , Proteínas de Neoplasias/genética , Proteínas de Neoplasias/metabolismo , Complexo de Endopeptidases do Proteassoma/química , Complexo de Endopeptidases do Proteassoma/genética , Subunidades Proteicas , Proteínas Recombinantes/genética , Proteínas Recombinantes/imunologia , Proteínas Recombinantes/metabolismo , Homologia de Sequência de AminoácidosRESUMO
A mixture of two new diterpenes was isolated from a dichloromethane extract of Croton zambesicus: ent-18-hydroxytrachyloban-3beta-ol (1) and ent-18-hydroxyisopimara-7,15-diene-3beta-ol (2). The two compounds crystallised together and were separated after derivatisation of the pimarane derivative with osmium tetroxide. The structure of 1 was elucidated by 1D- and 2D-NMR analysis and by X-ray diffraction of a crystal containing both compounds while 2 was only identified by crystallographic data. As this plant is widely used in African folk medicine against hypertension, we have analysed the vasorelaxant activity of the isolated molecules. The mixture of the two compounds inhibited the KCl-induced contraction of male Wistar rat aorta (IC (50) = 1 microg/mL), while the purified trachylobane (compound 1) and the hydroxylated pimarane showed a lower activity than the mixture.