ErbB-2 is a receptor found on the plasma membrane of mammalian cells. Recent stu
ID: 150253 • Letter: E
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 (see Giri et al., 2005, Mol. Cell Biol. 25:11005 11018.) In the first experiment, RNA interference (siRNA) is used to reduce levels of importin 1 (please see page numbers 264-266 MCB, Lodish 8th edition for details). Cells are either not subjected to siRNA(-), or have their expression of importin 1 reduced (imp), or are subjected to a nonsense siRNA (NS, siRNA that does not target importin or ErbB-2). The presence of ErbB-2 and importing B1, in both cytoplasmic and nuclear fractions is then analyzed by immunoblotting using antibodies against each of these proteins. 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 (DNLS) are immunoprecipitated with antibody to ErbB-2 or a control antibody (mIgG) (please see page numbers 112- 114 MCB, Lodish 8th edition for details). 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 SiRNAImp N.S. -Imp N.S Importin B1 ErbB-2 ErbB-2 What do these data suggest about the relationship between ErbB-2 and importin B1?Explanation / Answer
Importin 1 is required for ErbB-2 nuclear translocation.
Interaction between ErbB-2 and importin 1 was detected in the cytoplasmic extracts of ErbB-2.
The results were observed on immunoblot analysis.
On using interfering RNA treatment and analysis,
we can see that
the importin 1 protein level was specifically down-regulated, and ErbB-2 expression in the nuclear fraction was clearly reduced in cells transfected with importin 1 siRNA but not in mock-treated cells or cells transfected with nonspecific siRNA. Taken together, these data suggest that importin 1 is required for ErbB-2 translocation into the nucleus.
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