Breast Cancer
Mol
Cell Biol. 2006 Jun;26(11):4041-51. Cancer Res.
2006 May 15;66(10):5304-13.
Insulin-Like Growth Factor I Controls a
Mutually Exclusive Association of RACK1 with Protein Phosphatase
2A and {beta}1 Integrin To Promote Cell
Migration.
Kiely
PA, O'gorman
D, Luong
K, Ron
D, O'connor
R.
Cell Biology Laboratory, Department of Biochemistry, BioSciences
Institute, National University of Ireland, Cork, Ireland. r.oconnor@ucc.ie.
The WD repeat scaffolding protein RACK1 can mediate integration of the
insulin-like growth factor I receptor (IGF-IR) and integrin
signaling in transformed cells. To address the mechanism of RACK1 function,
we searched for regulatory proteins that associate with RACK1 in an
IGF-I-dependent manner. The serine threonine phosphatase protein phosphatase
2A (PP2A) was found associated with RACK1 in serum-starved cells, and it
dissociated immediately upon stimulation with IGF-I. This dissociation of
PP2A from RACK1 and an IGF-I-mediated decrease in cellular PP2A activity
did not occur in cells expressing either the serine 1248 or tyrosine
1250/1251 mutants of the IGF-IR that do not interact with RACK1.
Recombinant RACK1 could bind to PP2A in vitro and restore phosphatase activity to PP2A from IGF-I-stimulated
cells. Ligation of integrins
with fibronectin or Matrigel
was sufficient to facilitate IGF-I-mediated dissociation of PP2A from RACK1
and also to recruit beta1 integrin as PP2A
dissociated. By using TAT-fused N-terminal and C-terminal deletion mutants
of RACK1, we determined that both PP2A and beta1 integrin
interact in the C terminus of RACK1 within WD repeats 4 to 7. This suggests
that integrin ligation
displaces PP2A from RACK1. MCF-7 cells overexpressing
RACK1 exhibited enhanced motility, which could be reversed by the PP2A
inhibitor okadaic acid. Small interfering
RNA-mediated suppression of RACK1 also decreased the migratory capacity of
DU145 cells. Taken together, our findings indicate that RACK1 enhances
IGF-I-mediated cell migration through its ability to exclusively associate
with either beta1 integrin or PP2A in a complex
at the IGF-IR.
Epidermal Growth Factor Induces Insulin
Receptor Substrate-2 in Breast Cancer Cells via c-Jun NH2-Terminal Kinase/Activator Protein-1 Signaling to Regulate Cell
Migration.
Cui
X, Kim
HJ, Kuiatse I, Kim
H, Brown
PH, Lee
AV.
Breast Center, Departments of Medicine and Molecular and Cellular Biology,
Baylor College of Medicine and Methodist Hospital, Houston, Texas.
The epidermal growth factor (EGF) and insulin-like growth factor (IGF)
signaling pathways are critically involved in cancer development and
progression. However, how these two signals cross-talk with each other to
regulate cancer cell growth is not clearly understood. In this study, we
found that EGF remarkably induced expression of major IGF signaling
components, insulin receptor substrate (IRS)-1 and IRS-2, an effect that
could be blocked by EGF receptor (EGFR) tyrosine kinase
inhibitors. Although both extracellular
signal-regulated kinase and c-Jun NH(2)-terminal kinase (JNK) signaling pathways were involved in the
EGF up-regulation of IRS-1, the IRS-2 induction by EGF was specifically
mediated by JNK signaling. Consistent with this, EGF increased IRS-2
promoter activity, which was associated with recruitment of activator
protein-1 (AP-1) transcription factors and was inhibited by blocking AP-1
activity. Moreover, EGF treatment enhanced IGF-I and integrin
engagement-elicited tyrosine phosphorylation of
IRS and their downstream signaling, such as binding to phosphatidylinositol
3'-kinase regulatory subunit p85. Finally, repressing the induction of
IRS-2 levels abolished the EGF enhancement of cell motility, suggesting
that increased IRS-2 is essential for the EGF regulation of breast cancer
cell migration. Taken together, our results reveal a novel mechanism of
cross-talk between the EGF and IGF signaling pathways, which could have
implications in therapeutic applications of targeting EGFR in tumors.
Because AP-1 activity is involved in breast cancer progression, our work
may also suggest IRS-2 as a useful marker for aggressive breast cancer.
(Cancer Res 2006; 66(10): 5304-13).
PMID: 16707456 [PubMed - in process]