Autophosphorylation of JAK2 at tyrosine 813 in 3T3-F442A cells in response to GH. (A) 293T cells were transfected with cDNAs encoding either JAK2 or JAK2 with tyrosine 813 mutated to phenylalanine (Y813F). Cell lysates were immunoblotted with either anti-JAK2, anti-PY, or anti-P(Y813)JAK2. (B) 3T3-F442A cells were treated either with vehicle for 0 (lane 1) or 180 (lane 9) min or with GH (500 ng/ml) for 5, 15, 30, 60, 90, 120, or 180 min (lanes 2 through 8, respectively). Cell lysates were immunoblotted with either anti-P(Y813)-JAK2 (top panel), anti-PY (middle panel), or anti-JAK2 (bottom panel).