Journal Article

Graded activation of the MEK1/MT1-MMP axis determines renal epithelial cell tumor phenotype

Rajeev Mahimkar, Maria Alejandra Alfonso-Jaume, Leslie M. Cape, Rajvir Dahiya and David H. Lovett

in Carcinogenesis

Volume 32, issue 12, pages 1806-1814
Published in print December 2011 | ISSN: 0143-3334
Published online September 2011 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/bgr216
Graded activation of the MEK1/MT1-MMP axis determines renal epithelial cell tumor phenotype

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Activation of Raf/Ras/mitogen-activated protein kinase (MEK)/mitogen-activated protein kinase signaling and elevated expression of membrane type-1 matrix metalloproteinase (MT1-MMP) are associated with von Hippel–Lindau gene alterations in renal cell carcinoma. We postulated that the degree of MEK activation was related to graded expression of MT1-MMP and the resultant phenotype of renal epithelial tumors. Madin Darby canine kidney epithelial cells transfected with a MEK1 expression plasmid yielded populations with morphologic phenotypes ranging from epithelial, mixed epithelial/mesenchymal to mesenchymal. Clones were analyzed for MEK1 activity, MT1-MMP expression and extent of epithelial–mesenchymal transition. Phenotypes of the MDCK-MEK1 clones were evaluated in vivo with nu/nu mice. Tissue microarray of renal cell cancers was quantitatively assessed for expression of phosphorylated MEK1 and MT1-MMP proteins and correlations drawn to Fuhrman nuclear grade. Graded increases in the MEK signaling module were associated with graded induction of epithelial–mesenchymal transition of the MDCK cells and induction of MT1-MMP transcription and synthesis. Inhibition of MEK1 and MT1-MMP activity reversed the epithelial–mesenchymal transition. Tumors generated by epithelial, mixed epithelial/mesenchymal and mesenchymal MDCK clones demonstrated a gradient of phenotypes extending from well-differentiated, fully encapsulated non-invasive tumors to tumors with an anaplastic morphology, high Fuhrman nuclear score, neoangiogenesis and invasion. Tumor microarray demonstrated a statistically significant association between the extent of phosphorylated MEK1, MT1-MMP expression and nuclear grade. We conclude that graded increases in the MEK1 signaling module are correlated with M1-MMP expression, renal epithelial cell tumor phenotype, invasive activity and nuclear grade. Phosphorylated MEK1 and MT1-MMP may represent novel, and mechanistic, biomarkers for the assessment of renal cell carcinoma.

Journal Article.  6066 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

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