Western blot analysis of PSer¹³³-CREB and total CREB protein performed in HEL cells stimulated for 30 minutes with increasing concentrations of TPO. Cells were treated with 0 (negative control, lane 1), 1 (lane 2), 10 (lane 3), 100 (lane 4), or 500 (lane 5) ng/mL of TPO; 10 μmol/L forskolin (lane 6); or 10⁻⁷ mol/L PMA (lane 7). A representative experiment with the densitometric analysis expressed in arbitrary units (a.u.) is shown. The mean PSer¹³³-CREB densitometric values ± SD of five separate experiments were 13 ± 3.5 (lane 1), 21 ± 4.8 (lane 2), 36.5 ± 4.4 (lane 3), 41.5 ± 5.8 (lane 4), 32 ± 4.3 (lane 5), 45.6 ± 5.8 (lane 6), and 47.3 ± 5.1 (lane 7).