engleski

Fully conformed MHC class I molecules and empty Ld molecules follow different routes in the endocytic pathway

Problem. MHC class I molecules are present in the cell as “ full” trimolecular complexes composed of properly folded heavy chain,  2 – microglobulin ( 2m) and peptide (conformed MHC-I molecules), or “ empty” heavy chains devoid of peptide and often associated with  2m (no-conformed MHC-I molecules). The aim of our study was to compare the endocytic trafficking of conformed and non-conformed murine MHC-I molecules (Kd, Dd and Ld) in non-polarized cell lines. Methods of study. Endocytic trafficking of MHC-I molecules was followed in the model of spontaneous internalization after surface labeling with monoclonal antibodies (mAbs) or biotin. Intracellular pathway was dissected by treatment with inhibitors of vesicular transport and characterized by confocal microscopy and colocalization with endosomal markers. Surface biotinilation and immunoprecipitation was used to determine the kinetics of MHC-I degradation. Results. In the steady state, conformed and non-conformed MHC-I molecules partially colocalized. After internalization, both conformed and non-conformed molecules were found in sorting endosomes (SEs), but after that point they separated. Conformed MHC molecules were recycled through thejuxtanuclear recycling endosomes, whereas non-conformed MHC-I molecules were directed to an acidic endosomal retention compartment. From the retention compartment empty Ld molecules were directed either into lysosome for degradation or into the exocytic pathway. Conclusions. Conformed and non-conformed MHC-I molecules travel together to the sorting endosomes and separate into the different routes after they leave SEs. Conformed MHC-I molecules travel the recycling route and gradually enter the degradation pathway. Non-conformed molecules are retained in a late acidic multivesicular compartment from which they are sorted into the exocytcytic route or degradation pathway. The experiments are partially financed by Croatian Ministry of Science Grant No. 0620238-0223 and EMBIC project, European FP6, NoE, No. 512040, LSHM-CT-2004-512040.

MHC class I molecules; empty Ld molecules

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