Fig 1. Arsenite-induced dissociation of Hsp27 is suppressed by inhibitors of p38 MAP kinase but not MAP kinase kinase (MEK). U251 MG cells were exposed to 200 μM sodium arsenite (As) at 37°C for 90 minutes with or without 10 μM each of SB 203580 (SB), PD 169316 (PD16), PD 98059 (PD98), or Uo 126 (Uo). The cells were also exposed to each inhibitor alone under the same conditions. Each cell extract was fractionated by centrifugation on a sucrose density gradient (10–40%). The specimen in each tube was withdrawn from the bottom as 15 fractions, and 10-μL aliquots of each fraction were subjected in duplicate to the specific immunoassay described in “Materials and Methods.” Arrows indicate the positions at which β-d-galactosidase from Escherichia coli (Gal 540 kDa) and bovine serum albumin (BSA, 67 kDa) sedimented. Control, untreated cells. The data are representative of 3 separate experiments