Breast Cancer Research and Treatment

, Volume 100, Issue 1, pp 33–47 | Cite as

Proteasome Inhibitors Induce a p38 Mitogen-activated Protein Kinase (MAPK)-dependent Anti-apoptotic Program Involving MAPK Phosphatase-1 and Akt in Models of Breast Cancer

  • Yue Y. Shi
  • George W. Small
  • Robert Z. OrlowskiEmail author
Preclinical Study


Proteasome inhibitors represent a novel class of anti-tumor agents that have clinical efficacy against hematologic malignancies, but single-agent activity against solid tumors such as breast cancer has been disappointing, perhaps due to activation of anti-apoptotic survival signals. To evaluate a possible role for the p38 mitogen-activated protein kinase (MAPK), A1N4-myc human mammary epithelial, and BT-474 and MDA-MB-231 breast carcinoma cells, were studied. Exposure of these lines to pharmacologic p38 blockade enhanced proteasome inhibitor-mediated apoptosis, as did overexpression of dominant negative (DN)-p38-α and -β-MAPK isoforms. Inhibition of p38 resulted in suppression of induction of anti-apoptotic MAPK phosphatase (MKP)-1, in association with enhanced activation of the pro-apoptotic c-Jun-N-terminal kinase (JNK). Moreover, infection of cells treated with a proteasome inhibitor/p38 inhibitor combination with Adenovirus (Ad) inducing over-expression of MKP-1 suppressed apoptosis compared with controls. Further targets of p38 MAPK were also studied, and proteasome inhibition activated phosphorylation of MAPK-activated protein kinase-2, heat shock protein (HSP)-27, and the AKT8 virus oncogene cellular homolog (Akt). Inhibition of p38 MAPK resulted in decreased phospho-HSP-27 and phospho-Akt, while down-regulation of HSP-27 with a small interfering RNA decreased phosphorylation of Akt, directly linking activation of p38 to Akt. Finally, inhibition of Akt with phosphatidylinositol-3-kinase inhibitors increased apoptosis, as did over-expression of DN-Akt. These studies support the hypothesis that proteasome inhibitors activate an anti-apoptotic survival program through p38 MAPK that involves MKP-1 and Akt. Further, they suggest that strategies targeting MKP-1 and Akt could enhance the anti-tumor efficacy of proteasome inhibitors against breast cancer.


Akt Bortezomib MKP-1 p38 MAPK Proteasome 





AKT8 virus oncogene cellular homolog








dominant negative


enzyme-linked immunosorbent assay


estrogen receptor


fluorescein isothiocyanate


green fluorescent protein


glycogen synthase kinase


heat shock cognate protein


heat shock protein


c-Jun-N-terminal kinase




mitogen-activated protein kinase


MAPK-activated protein kinase


mitogen-activated protein kinase phosphatase


phosphate-buffered saline


phosphoinositide-dependent protein kinase


propidium iodide




phenylmethylsulfonyl fluoride


small interfering RNA targeting HSP-27


small interfering RNA with a scrambled sequence that does not target HSP-27




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The authors would like to gratefully acknowledge the generosity of Dr. Jiahuai Han (Scripps Research Institute; La Jolla, CA) for providing dominant negative mutant p38 MAPK isoform constructs, and Dr. Kenneth Walsh (Boston University School of Medicine; Boston, MA) for providing Adenoviral vectors directing expression of dominant negative Akt. R.Z.O, a Leukemia and Lymphoma Society Scholar in Clinical Research (2201-06), and a Jefferson-Pilot Fellow in Academic Medicine, would also like to acknowledge support for these studies from the National Cancer Institute (RO1 CA102278).


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Copyright information

© Springer Science+Business Media B.V. 2006 2006

Authors and Affiliations

  • Yue Y. Shi
    • 1
  • George W. Small
    • 1
  • Robert Z. Orlowski
    • 1
    • 2
    • 3
    Email author
  1. 1.22-003 Lineberger Comprehensive Cancer CenterUniversity of North Carolina at Chapel HillChapel HillUSA
  2. 2.Department of Medicine, Division of Hematology/OncologyUniversity of North Carolina at Chapel HillChapel HillUSA
  3. 3.Department of PharmacologyUniversity of North Carolina at Chapel HillChapel HillUSA

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