title: Localization of importin alpha (Rch1) at the plasma membrane and subcellular redistribution during lymphocyte activation.
abstract: Rch1 belongs to the importin alpha subfamily and works as an adapter between karyophilic proteins and the nuclear import machinery. Its level of expression varies among species and tissues, and depends on the state of cellular metabolism. In the present study we examined the level of expression of nuclear envelope and nuclear transport proteins (Rch1, importin beta, lamins A/C, lamin B, gp210, p62 and transportin) after human lymphocyte activation with phytohemagglutinin. We observed that the level of Rch1 increases dramatically, especially in larger lymphocytes, in response to activation. Moreover, using immunoelectron microscopy, this nuclear transport factor was found to be localized at the plasma membrane and also in tracks from the cytoplasm through the nuclear envelope into the nucleus. Similar localization was also observed in the human melanoma cell line A375. In addition, metabolic activation led to a redistribution of Rch1 from the cytoplasm to both the plasma membrane and the nuclear interior. These results suggest that, during lymphocyte activation, Rch1 may be involved in a signal transduction pathway that involves the shuttling of karyophilic proteins from the plasma membrane to the nucleus.
authors.affiliation: Department of Cell Biology and Histology, University of the Basque Country, Medical School, 48940 Leioa, Vizcaya, Spain.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Andrade
authors.forename: Raúl
authors.initials: R
authors.lastname: Alonso
authors.forename: Raúl
authors.initials: R
authors.lastname: Peña
authors.forename: Jon
authors.initials: J
authors.lastname: Arlucea
authors.forename: Juan
authors.initials: J
authors.lastname: Aréchaga
mesh_terms: D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism* / Q000648:ultrastructure; D002467:Cell Nucleus / Q000378:metabolism / Q000648:ultrastructure; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism / Q000648:ultrastructure; D006801:Humans; D007150:Immunohistochemistry; D008213:Lymphocyte Activation; D008214:Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008545:Melanoma / Q000378:metabolism / Q000648:ultrastructure; D009685:Nuclear Envelope / Q000378:metabolism / Q000648:ultrastructure; D010835:Phytohemagglutinins / Q000494:pharmacology; D028901:alpha Karyopherins / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D010835:Phytohemagglutinins; D028901:alpha Karyopherins