Von Hippel-Lindau tumor suppressor gene loss in renal cell carcinoma promotes oncogenic epidermal growth factor receptor signaling via Akt-1 and MEK-1.
OBJECTIVE
Clear-cell renal cell carcinoma (RCC) is the most prevalent form of kidney cancer and is frequently associated with loss of von Hippel-Lindau (VHL) gene function, resulting in the aberrant transcriptional activation of genes that contribute to tumor growth and metastasis, including transforming growth factor-alpha (TGF-alpha), a ligand of the epidermal growth factor receptor (EGFR) tyrosine kinase. To determine the functional impact of EGFR activation on RCC, we suppressed critical components of this pathway: EGFR, Akt-1, and MEK-1.


METHODS
Stable transfection of RCC cells with plasmids bearing shRNA directed against each of these genes was used to individually suppress their expression. Transfectants were characterized for growth and invasiveness in vitro and tumorigenesis in vivo.


RESULTS
RCC cell transfectants displayed significantly reduced growth rate and matrix invasion in vitro and RCC tumor xenograft growth rate in vivo. Analysis of tumor cells that emerged after extended periods in each model showed that significant EGFR suppression was sustained, whereas Akt-1 and MEK-1 knock-down cells had escaped shRNA suppression.


CONCLUSIONS
EGFR, Akt-1, and MEK-1 are individually critical for RCC cell invasiveness in vitro and tumorigenicity in vivo, and even partial suppression of each can have a significant impact on tumor progression. The emergence of transfectants that had escaped Akt-1 and MEK-1 suppression during tumorigenicity experiments suggests that these effectors may each be more critical than EGFR for RCC tumorigenesis, consistent with results from clinical trials of EGFR inhibitors for RCC, where durable clinical responses have not been seen.
Lee
S Justin
SJ
Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA.
Lattouf
Jean-Baptiste
JB
Xanthopoulos
Julie
J
Linehan
W Marston
WM
Bottaro
Donald P
DP
Vasselli
James R
JR
D000818:Animals; D002292:Carcinoma, Renal Cell / Q000235:genetics / Q000473:pathology; D049109:Cell Proliferation; D066246:ErbB Receptors / Q000502:physiology*; D006801:Humans; D007680:Kidney Neoplasms / Q000235:genetics; D048369:MAP Kinase Kinase 1 / Q000502:physiology*; D008297:Male; D051379:Mice; D016513:Mice, SCID; D009361:Neoplasm Invasiveness; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology*; D015398:Signal Transduction; D014407:Tumor Cells, Cultured; D006623:von Hippel-Lindau Disease / Q000235:genetics / Q000473:pathology
C512478:EGFR protein, human; D066246:ErbB Receptors; D051057:Proto-Oncogene Proteins c-akt; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human