Mutant S400A of Hsp70 rescues MDS erythroblast differentiation. (A) Hsp70 S400A preferentially localizes to the nucleus. Normal erythroblasts transfected with HA-wtHsp70 or HA-Hsp70 S400A plasmids. Immunofluorescence anti-HA analyzed by confocal microscopy. (B) Immunoblot analysis of Hsp70 and GATA-1 expression. MDS erythroblasts infected with wtHsp70 or Hsp70 S400A or empty lentiviral vector at day 14. (Top panel) Representative immunoblot. (Bottom panel) Quantification of GATA-1 normalized to Hsc70 by densitometry. (C) Immunofluorescence for Hsp70 and GATA-1 in day 14 erythroblasts. MDS (n = 9) or control (n = 4) erythroblasts were infected with wtHsp70 or Hsp70 S400A or empty lentiviral vector. Nuclei countercolored with DAPI. (D) Apoptosis. Annexin V labeling in the GFP⁺ cells. (E) Erythroid differentiation. Differentiated polychromatophilic and acidophilic erythroblasts numbered on MGG-stained cytospins. Representative microphotographs are shown. Student t test for P values; *P < .05; **P < .01; ns indicates not significant.