ATG5 is required for B cell polarization and presentation of particulate antigens.

ABSTRACT

The involvement of macroautophagy/autophagy proteins in B-cell receptor (BCR) trafficking, although suspected, is not well understood. We show that ATG5 (autophagy related 5) contributes to BCR polarization after stimulation and internalization into LAMP1 (lysosomal-associated membrane protein 1)+ and major histocompatibility complex class II (MHC-II)+ compartments. BCR polarization is crucial in the context of immobilized antigen processing. Moreover, antigen presentation to cognate T cells is decreased in the absence of ATG5 when the model antigen OVAL/ovalbumin is provided in an immobilized form in contrast to the normal presentation of soluble OVAL. We further show that ATG5 is required for centrosome polarization and actin nucleation in the immune synapse area. This event is accompanied by an increased interaction between ATG16L1 (autophagy related 16-like 1 [S. cerevisiae]) and the microtubule-organizing center-associated protein PCM1 (pericentriolar material 1). In the human B cell line BJAB, PCM1 is required for BCR polarization after stimulation. We thus propose that the ATG12 (autophagy related 12)-ATG5-ATG16L1 complex under BCR stimulation allows its interaction with PCM1 and consequently facilitates centrosome relocalization to the immune synapse, optimizing the presentation of particulate antigens. Abbreviations ACTB actin beta; ACTR2/3 ARP2/3 actin-related protein 2/3; APC antigen-presenting cells; ATG autophagy-related; BCR B cell receptor; BECN1/Beclin 1 beclin 1, autophagy related; CDC42 cell division cycle 42; Cr2 complement receptor 2; CSFE carboxyfluorescein succinimidyl ester; DAPI 4',6-diamidino-2-phenylindole dihydrochloride; EEA1 early endosome antigen 1; ELISA enzyme-linked immunosorbent assay; FITC fluorescein isothyocyanate; GC germinal center; GJA1/CX3 gap junction protein, alpha 1; Ig immunoglobulin; LAMP1 lysosomal-associated membrane protein 1; LAP LC3-associated phagocytosis; LM littermate; MAP1LC3/LC3 microtubule-associated protein 1 light chain 3; MAPK/ERK mitogen activated protein kinase; MHC-II major histocompatibility complex class II; MIIC MHC class II compartment; OVAL ovalbumin; PBS phosphate-buffered saline; PCM1 pericentriolar material 1; PtdIns3K phosphatidylinositol 3-kinase; PTPRC/CD45RB/B220; Protein tyrosine phosphatase, receptor type, C; SYK spleen tyrosine kinase; TBS Tris-buffered saline; TCR T cell receptor; ULK1 unc-51 like kinase 1.