ERBB4-truncated forms show oncogenic potentials in NIH-3T3 cells. (A) NIH-3T3 cells transduced with the indicated constructs were analyzed for cell cycle after serum deprivation (72 hours). I12Δ- and I20Δ+I12Δ-transduced cells displayed reduced G0/G1 arrest compared to controls. (B) Focus formation assay of NIH-3T3 cells transduced with the indicated constructs. I12ΔERBB4 transformation potential is kinase dependent as suggested by ERBB4 kinase dead construct (I12ΔK751M) expression and lapatinib treatment. (C) Soft agar assay of NIH-3T3 cells transduced with the indicated constructs. Increased numbers of colonies were detected in I12Δ-, I20Δ+I12Δ-, and NPM-ALK–transduced cells. (D) Tumor growth curves of NIH3T3 cells transduced with the indicated constructs. A total of 5 × 10⁴ cells were subcutaneously injected into 6 NSG mice for each condition. Tumor growth was monitored over time by determining the volume of tumor masses. Each data point represents the average tumor volume (mean ± standard error). P.I., propidium iodide.