Western blot analysis of PSer¹³³-CREB and total CREB protein performed in HEL stimulated with 100 ng/mL of TPO for various time points. Cells were left untreated (negative control, lane 1) or treated with 100 ng/mL of TPO for 1 (lane 2), 5 (lane 3), 15 (lane 4), 30 (lane 5), or 60 minutes (lane 6) or with 10⁻⁷ mol/L PMA for 30 minutes (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 four separate experiments were 12.4 ± 2.9 (lane 1), 18.3 ± 3.9 (lane 2), 46.1 ± 5.1 (lane 3), 47.9 ± 6.3 (lane 4), 46 ± 5.2 (lane 5), 35.9 ± 5.2 (lane 6), and 62.3 ± 7.4 (lane 7).