The stimulus-dependent co-localization of serum- and glucocorticoid-regulated protein kinase (Sgk) and Erk/MAPK in mammary tumor cells involves the mutual interaction with the importin-alpha nuclear import protein

Patricia Buse, Anita C. Maiyar, Kim L. Failor, Susan Tran, Meredith L L Leong, Gary L. Firestone

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

In Con8 rat mammary epithelial tumor cells, indirect immunofluorescence revealed that Sgk (serum- and glucocorticoid-regulated kinase) and Erk/MAPK (extracellular signal-regulated protein kinase/mitogen activated protein kinase) co-localized to the nucleus in serum-treated cells and to the cytoplasmic compartment in cells treated with the synthetic glucocorticoid dexamethasone. Moreover, the subcellular distribution of the importin-alpha nuclear transport protein was similarly regulated in a signal-dependent manner. In vitro GST-pull down assays revealed the direct interaction of importin-alpha with either Sgk or Erk/MAPK, while RNA interference knockdown of importin-alpha expression disrupted the localization of both Sgk and Erk into the nucleus of serum-treated cells. Wild type or kinase dead forms of Sgk co-immunoprecipitated with Erk/MAPK from either serum- or dexamethasone-treated mammary tumor cells, suggesting the existence of a protein complex containing both kinases. In serum-treated cells, nucleus residing Sgk and Erk/MAPK were both hyperphosphorylated, indicative of their active states, whereas, in dexamethasone-treated cells Erk/MAPK, but not Sgk, was in its inactive hypophosphorylated state. Treatment with a MEK inhibitor, which inactivates Erk/MAPK, caused the relocalization of both Sgk and ERK to the cytoplasm. We therefore propose that the signal-dependent co-localization of Sgk and Erk/MAPK mediated by importin-alpha represents a new pathway of signal integration between steroid and serum/growth factor-regulated pathways.

Original languageEnglish (US)
Pages (from-to)3261-3275
Number of pages15
JournalExperimental Cell Research
Volume313
Issue number15
DOIs
StatePublished - Sep 10 2007
Externally publishedYes

Fingerprint

alpha Karyopherins
Cell Nucleus Active Transport
Extracellular Signal-Regulated MAP Kinases
Nuclear Proteins
Mitogen-Activated Protein Kinases
Protein Kinases
Breast Neoplasms
Dexamethasone
Serum
Phosphotransferases
serum-glucocorticoid regulated kinase
Mitogen-Activated Protein Kinase Kinases
Indirect Fluorescent Antibody Technique
RNA Interference
Cell Nucleus
Glucocorticoids
Signal Transduction
Intercellular Signaling Peptides and Proteins
Carrier Proteins
Cytoplasm

Keywords

  • Glucocorticoids
  • Importin-alpha
  • Nuclear/cytoplasmic localization
  • Protein kinase
  • Steroid and growth factor signal integration

ASJC Scopus subject areas

  • Cell Biology

Cite this

The stimulus-dependent co-localization of serum- and glucocorticoid-regulated protein kinase (Sgk) and Erk/MAPK in mammary tumor cells involves the mutual interaction with the importin-alpha nuclear import protein. / Buse, Patricia; Maiyar, Anita C.; Failor, Kim L.; Tran, Susan; Leong, Meredith L L; Firestone, Gary L.

In: Experimental Cell Research, Vol. 313, No. 15, 10.09.2007, p. 3261-3275.

Research output: Contribution to journalArticle

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abstract = "In Con8 rat mammary epithelial tumor cells, indirect immunofluorescence revealed that Sgk (serum- and glucocorticoid-regulated kinase) and Erk/MAPK (extracellular signal-regulated protein kinase/mitogen activated protein kinase) co-localized to the nucleus in serum-treated cells and to the cytoplasmic compartment in cells treated with the synthetic glucocorticoid dexamethasone. Moreover, the subcellular distribution of the importin-alpha nuclear transport protein was similarly regulated in a signal-dependent manner. In vitro GST-pull down assays revealed the direct interaction of importin-alpha with either Sgk or Erk/MAPK, while RNA interference knockdown of importin-alpha expression disrupted the localization of both Sgk and Erk into the nucleus of serum-treated cells. Wild type or kinase dead forms of Sgk co-immunoprecipitated with Erk/MAPK from either serum- or dexamethasone-treated mammary tumor cells, suggesting the existence of a protein complex containing both kinases. In serum-treated cells, nucleus residing Sgk and Erk/MAPK were both hyperphosphorylated, indicative of their active states, whereas, in dexamethasone-treated cells Erk/MAPK, but not Sgk, was in its inactive hypophosphorylated state. Treatment with a MEK inhibitor, which inactivates Erk/MAPK, caused the relocalization of both Sgk and ERK to the cytoplasm. We therefore propose that the signal-dependent co-localization of Sgk and Erk/MAPK mediated by importin-alpha represents a new pathway of signal integration between steroid and serum/growth factor-regulated pathways.",
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AU - Firestone, Gary L.

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