engleski

Endocytic pathways of MHC class I molecules

Surface glycoproteins are a constitutive part of the cell membrane and their equilibrium is achived by a balance between new synthesis and regulated processes of their removal from the cell surface, such as internalisation by endocytosis, and the subsequent degradation. Surface glyckoproteins can be internalised constitutively (spontaneously) and their internalisation can be induced by binding of a ligand, ie. antibody or some other external molecule. The same molecule could be internalised by different mechanism in the constitutive and in induced pathways. Endocytic mechanism of cellular glycoproteins are different, but mostly involve two types : regulated internalisation (clathrin endocytosis and caveolae-mediated endocytosis) and fluid phase endocytosis. Endocytosis of MHC class I molecules was studied under conditions of spontaneous internalisation after treatment with cycloheximide, and induced internalisation after binding of specific monoclonal antibodies. MHC class I alleles differs regarding their stability, kinetics, and the way of internalisation and degradation. Kd and Dd molecules are more stable than Ld molecules and have longer surface half-life. Internalisation mechanism of fully conformed Ld molecules (full) differs from internalisation of non-conformed Ld molecules (empty). A majority of internalised MHC class I molecules are recycled, and only a smaller part is degraded.

Endocytosis; MHC class I molecules; vesicular transport; alternative peptide presentation

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