GH augments acute GHR-GHR complementation but fails to cause a subsequent decline in complementation in JAK2-deficient cells. A, JAK2-deficient cells lack GH-induced phosphorylation of GHR-Nluc, JAK2, and STAT5. Serum-starved JAK2-deficient γ2A-GHR-Nluc cells were treated ±GH (500 ng/mL, 10 min). Detergent cells extracts were resolved by SDS-PAGE and sequentially immunoblotted with anti-pY, anti-GHRcyt-AL47, anti-p-JAK2, anti-JAK2AL33, anti-p-STAT5, and anti-STAT5. GHR-Nluc is indicated by a bracket. The positions of JAK2, pJAK2, STAT5, and pSTAT5 are indicated by arrows. Note the absence of phosphorylated GHR-Nluc, JAK2, or STAT5 and the lack of JAK2. The blot shown is representative of two such experiments. B, JAK2 deficiency prevents the decline in GH-induced GHR-GHR complementation. γ2A-GHR-Nluc cells transiently expressing GHR-Cluc were treated with GH (500 ng/mL) after basal bioluminescence was determined. Bioluminescence was measured serially thereafter over 40 minutes. Data are expressed as mean ± SE of GH-induced signal as a percentage above baseline signal (n = 3 per condition). The figure shown is representative of three such experiments.