Question

Cycloheximide inhibits protein synthesis. Which of the following steps in the EGF signaling pathway would still occur if otherwise normal cells with normal HER1 were treated simultaneously with EGF and cycloheximide?

A. Activation of HER1 receptor by EGF binding.

B. Internalization of the EGF-HER1 complex.

C. Phosphorylation of HER1 intracellular domain.

D. Translocation of phosphorylated HER1 to the cell nucleus.

Answer 1

With EGF and cycloheximide treatment, activation of the HER1 receptor, internalization of the EGF-HER1 complex, and phosphorylation of the HER1 intracellular domain would still occur, as they do not require protein synthesis; translocation of HER1 to the nucleus, however, likely would be inhibited. Therefore, the correct option is A, B, C.

Step-by-step explanation:

If cells with normal HER1 are treated with EGF and cycloheximide, which inhibits protein synthesis, certain steps in the EGF signaling pathway would still occur. Cycloheximide affects the synthesis of proteins but does not impede the initial steps in signaling pathways that are non-protein synthesis dependent. Therefore, the following processes in the EGF signaling pathway would still take place:

Activation of HER1 receptor by EGF binding. This is a ligand-receptor interaction that does not require new protein synthesis.

Internalization of the EGF-HER1 complex. This process involves the endocytosis of the activated receptor and is also independent of protein synthesis.

Phosphorylation of HER1 intracellular domain. This post-translational modification occurs immediately after receptor activation and does not require new protein synthesis.

However, the translocation of phosphorylated HER1 to the cell nucleus often involves new protein synthesis and would likely be inhibited by cycloheximide.