Role of TpoR cytosolic residues Y78 and Y112 in the proliferation induced in Ba/F3 cells by TpoR signaling. Proliferation of cells expressing either TpoRwt or the corresponding Y→F mutants, Δ5TpoR or the corresponding Y→F mutants (A), or TpoR W515A or the corresponding Y→F mutants (B) was examined after 4 days in the presence of 3 ng/mL Tpo. Shown are averages of triplicates ± SD of 1of 3 representative experiments. Proliferation of cells expressing Δ5TpoR (C) or TpoRW515A mutants (D) in the absence of any cytokine was examined after 8 days. Shown are averages of triplicates ± SD of 1 of 3 representative experiments. (E) Proliferation of Ba/F3 expressing either Δ5TpoR, TpoRW515A, TpoRW515K, or TpoRW515L in the absence of cytokine. Cell growth was measured using the Cell Titer Glo Kit (Promega). Shown are averages of absorbance units of triplicates ± SD obtained from 1 of 2 representative experiments. (F) The Y112F mutation inhibits proliferation induced in the absence of Tpo by TpoRW515L and TpoRW515K mutants. Shown are averages of cell counts performed in triplicates ± SD obtained from 1 of 2 representative experiments.