Effects of Dex and/or IL-6 on p21 protein expression in MM cell lines and patient MM cells. Cells (2 × 105/mL) from IL-6–responsive MM-derived cell lines (OCI-My5, S6B45, and U-266; A) and IL-6–nonresponsive MM cell lines (HS Sultan and RPMI-8226) and JKB ALL cell line (B); 1 × 106/mL IL-6–responsive patient MM cells (patients no. 1, 3, and 5; C) and IL-6–nonresponsive patient MM cells (patients no. 2 and 4; D); 2 × 105/mL IL-6–nonresponsive Dex-resistant ARH-77 MM cells (E); and 1 × 106/mL normal BMMCs and splenic B cells (F ) were cultured with 10% FBS media alone, IL-6 (50 ng/mL), Dex (1 μmol/L), or Dex (1 μmol/L) and IL-6 (50 ng/mL). Total cell lysates were prepared 16 hours later and immunoprecipitated with anti-p21 or anti-p27 polyclonal Abs, followed by Western immunoblotting with anti-p21 or anti-p27 MoAbs. Immunoprecipitation and immunoblotting with anti-actin MoAb confirmed equal protein loading in cells that lacked detectable p21 and p27: ARH-77 (E) and normal BMMCs and splenic B cells (F ).
