HSP90 and HSP70 interact with PABPN1.
(A-C) A17-PABPN1 induced INIs in C2C12 cells. Mouse muscle C2C12 myoblasts were transfected with 0.5 μg GFP-tagged A10-PABPN1 or A17-PABPN1 constructs by lipofectamine 2000. Twenty-four hours post-transfection, myoblasts were fixed with 4% PFA, and the nuclei were stained with DAPI (blue). A10-PABPN1 formed small inclusions in nuclear speckles (arrows) whereas A17-PABPN1 formed large INIs (A). Scale bar, 10 μm. Myoblasts were switched to differentiation medium 24 hr after transfection. Fully differentiated myotubes were fixed and stained with DAPI. INIs formed by A10-PABPN1 and A17-PABPN1 are indicated by arrows (B). Cells in 10 random fields with INIs in the nucleus were scored (C). Data are shown as the mean ± SEM, n = 5; *, P < 0.01. (D) Interaction of PABPN1 with HSP90. Lysates from HEK293 cells transfected with Flag-HSP90 and GFP-tagged A17-PABPN1 were immunoprecipitated with an anti-Flag antibody. Immunoprecipitates (IP) were analyzed by Western blot (IB). (E) Interaction of PABPN1 with HSP70. Lysates from HEK293 cells transfected with Flag-HSP70 and GFP-tagged A17-PABPN1 were immunoprecipitated with an anti-Flag antibody. (F) HSP90 associates with the PABPN1 aggregates. C2C12 myoblasts were transfected with A17-PABPN1 constructs, and the cells were processed for immunofluorescence staining using a HSP90 antibody 48 hr after transfection. Arrows indicate the recruitment of HSP90 to the PABPN1 aggregates. Scale bar, 10 μm.