Breast Cancer Research and Treatment

, Volume 100, Issue 1, pp 33–47

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. Orlowski
Preclinical Study

DOI: 10.1007/s10549-006-9232-x

Cite this article as:
Shi, Y.Y., Small, G.W. & Orlowski, R.Z. Breast Cancer Res Treat (2006) 100: 33. doi:10.1007/s10549-006-9232-x

Abstract

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.

Keywords

AktBortezomibMKP-1p38 MAPKProteasome

Abbreviations

Ad

Adenoviral

Akt

AKT8 virus oncogene cellular homolog

β-Gal

β-galactosidase

CMV

cytomegalovirus

DMSO

dimethyl-sulfoxide

DN

dominant negative

ELISA

enzyme-linked immunosorbent assay

ER

estrogen receptor

FITC

fluorescein isothiocyanate

GFP

green fluorescent protein

GSK

glycogen synthase kinase

HSC

heat shock cognate protein

HSP

heat shock protein

JNK

c-Jun-N-terminal kinase

luc

luciferase

MAPK

mitogen-activated protein kinase

MAPKAPK

MAPK-activated protein kinase

MKP

mitogen-activated protein kinase phosphatase

PBS

phosphate-buffered saline

PDK

phosphoinositide-dependent protein kinase

PI

propidium iodide

PI3K

phosphatidylinositol-3-kinase

PMSF

phenylmethylsulfonyl fluoride

siHSP-27

small interfering RNA targeting HSP-27

ssRNA

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

Z-LLF-CHO

benzyloxycarbonyl-leucyl-leucyl-phenylalaninal

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
  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