ErbB-2 is a receptor found on the plasma membrane of mammalian cells. Recent stu

Question

ErbB-2 is a receptor found on the plasma membrane of mammalian cells. Recent studies have shown that this protein can move from the plasma membrane to the nucleus. Because most proteins that shuttle between the cytoplasm and the nucleus are soluble and not integral membrane proteins, the mechanism by which ErbB2 undergoes this transport is of particular interest. In the first experiment, RNA interference (siRNA) is used to reduce levels of importin ?1. Cells are either not subjected to siRNA (), or have their expression of importin B1 reduced (imp), or are subjected to a nonsense siRNA (NS). The presence of ErbB-2 is then analyzed by immunoblotting. The data are shown on the immunoblot below in Figure (a). In the second experiment, lysates of cells expressing either wild- type (WT) ErbB-2 or mutant ErbB-2 lacking its nuclear localization signal (ANLS) are immunoprecipitated with antibody to ErbB-2 or a control antibody (mlgG). The immunoprecipitates are then examined by immunoblotting with antibodies to importin B1 or to ErbB-2 as shown in Figure (b) (b) WT ANLS Cytoplasmic Nuclear SiRNA mp N.S. -Imp N | |--| Importin ?1 Importin B1 ErbB-2 What do these data suggest about the relationship between ErbB-2 and importin B1?

Explanation / Answer

Importin- ? family proteins are NTRs (nucleocytoplasmic transport receptors). these help in import and export of the other proteins and RNAs with the help of nuclear pores. The given experimental data is showing that ErbB-2 is transported through the importin- ? protein. So, importin- ? is the transporter of ErbB-2 receptor protein. The expression of importin- ? found to be low as maximum concentration of it binds to the ErbB-2.

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