3-phosphoinositide-dependent protein kinase-1 (PDK1) promotes invasion and activation of matrix metalloproteinases.
BACKGROUND
Metastasis is a major cause of morbidity and mortality in breast cancer with tumor cell invasion playing a crucial role in the metastatic process. PDK1 is a key molecule that couples PI3K to cell proliferation and survival signals in response to growth factor receptor activation, and is oncogenic when expressed in mouse mammary epithelial cells. We now present evidence showing that PDK1-expressing cells exhibit enhanced anchorage-dependent and -independent cell growth and are highly invasive when grown on Matrigel. These properties correlate with induction of MMP-2 activity, increased MT1-MMP expression and a unique gene expression profile.


METHODS
Invasion assays in Matrigel, MMP-2 zymogram analysis, gene microarray analysis and mammary isografts were used to characterize the invasive and proliferative function of cells expressing PDK1. Tissue microarray analysis of human breast cancers was used to measure PDK1 expression in invasive tumors by IHC.


RESULTS
Enhanced invasion on Matrigel in PDK1-expressing cells was accompanied by increased MMP-2 activity resulting from stabilization against proteasomal degradation. Increased MMP-2 activity was accompanied by elevated levels of MT1-MMP, which is involved in generating active MMP-2. Gene microarray analysis identified increased expression of the ECM-associated genes decorin and type I procollagen, whose gene products are substrates of MT1-MMP. Mammary fat pad isografts of PDK1-expressing cells produced invasive adenocarcinomas. Tissue microarray analysis of human invasive breast cancer indicated that PDK1pSer241 was strongly expressed in 90% of samples.


CONCLUSIONS
These results indicate that PDK1 serves as an important effector of mammary epithelial cell growth and invasion in the transformed phenotype. PDK1 mediates its effect in part by MT1-MMP induction, which in turn activates MMP-2 and modulates the ECM proteins decorin and collagen. The presence of increased PDK1 expression in the majority of invasive breast cancers suggests its importance in the metastatic process.
Department of Oncology, Georgetown University School of Medicine, and Lombardi Comprehensive Cancer Center, Washington, DC, USA. xiez@niaid.nih.gov
Zhihui
Z
Xie
Hongyan
H
Yuan
Yuzhi
Y
Yin
Xiao
X
Zeng
Renkui
R
Bai
Robert I
RI
Glazer
D064413:3-Phosphoinositide-Dependent Protein Kinases; D000818:Animals; D015153:Blotting, Western; D002448:Cell Adhesion; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D003094:Collagen / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D004338:Drug Combinations; D004789:Enzyme Activation; D005786:Gene Expression Regulation; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007150:Immunohistochemistry; D007797:Laminin / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D008156:Luciferases / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000166:cytology; D053511:Matrix Metalloproteinase 14; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism*; D020782:Matrix Metalloproteinases / Q000378:metabolism*; D053504:Matrix Metalloproteinases, Membrane-Associated; D051379:Mice; D008807:Mice, Inbred BALB C; D009361:Neoplasm Invasiveness; D009362:Neoplasm Metastasis; D009368:Neoplasm Transplantation; D020411:Oligonucleotide Array Sequence Analysis; D010957:Plasmids / Q000378:metabolism; D016133:Polymerase Chain Reaction; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism / Q000502:physiology*; D011509:Proteoglycans / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction
D004338:Drug Combinations; D007797:Laminin; C507096:Mmp14 protein, mouse; D011509:Proteoglycans; C059485:matrigel; D003094:Collagen; D008156:Luciferases; D064413:3-Phosphoinositide-Dependent Protein Kinases; C578562:PDPK1 protein, human; C578564:Pdpk1 protein, mouse; D017346:Protein Serine-Threonine Kinases; D020782:Matrix Metalloproteinases; D053504:Matrix Metalloproteinases, Membrane-Associated; D020778:Matrix Metalloproteinase 2; D053511:Matrix Metalloproteinase 14