Epidermal Growth Factor Receptor Signaling to the Mitogen Activated Protein Kinase Pathway Bypasses Ras in Pancreatic Cancer Cells.
OBJECTIVE
Epidermal growth factor (EGF) receptor (EGFR/HER1) is overexpressed in human pancreatic cancers. However, anti-EGFR therapy does not exhibit significant therapeutic activity with oncogenic K-ras mutation. We sought to assess the signaling relationship between EGFR and mutant K-ras, which is commonly detected in pancreatic cancer.


METHODS
Pancreatic cancer cells harboring mutated K-ras were treated with EGF to assess signaling from EGFR to mitogen-activated protein kinase (MAPK) pathway. The role of Ras family of proteins in transducing EGFR signals was assessed using short interfering RNA. Other components of MAPK and PI3K (phosphoinositide 3-kinase) pathways were examined for their roles in EGFR signaling.


RESULTS
First, EGF signaling in pancreatic cancer cells occurs selectively through HER1. Second, knockdown of all Ras isoforms failed to block EGF-mediated phosphorylation of extracellular signal-regulated kinase (ERK). Inhibition of Raf was observed to partially abrogate ERK phosphorylation, whereas MEK inhibition resulted in complete attenuation of EGF-mediated ERK phosphorylation. Finally, inhibition of phosphoinositide 3-kinase/AKT and CDC42/PAK pathways did not block EGFR signaling.


CONCLUSIONS
Our study results demonstrate that EGFR-mediated signaling in mutant K-ras pancreatic cancer cells does not follow canonical MAPK signaling. Our novel findings suggest the existence of alternate signaling pathways to downstream MAPK in the presence of mutant K-ras.
From the *Division of Surgical Oncology, Departments of Surgery and †Medical Oncology and Experimental Therapeutics, City of Hope National Medical Center, Duarte, CA; and ‡Department of Surgery, Stony Brook Medicine, Stony Brook, NY.
Sangjun
S
Lee
Eileen L
EL
Heinrich
Jianming
J
Lu
Wendy
W
Lee
Audrey H
AH
Choi
Carrie
C
Luu
Vincent
V
Chung
Marwan
M
Fakih
Joseph
J
Kim
D045744:Cell Line, Tumor; D004815:Epidermal Growth Factor / Q000494:pharmacology; D066246:ErbB Receptors / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D020935:MAP Kinase Signaling System; D009154:Mutation; D010190:Pancreatic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D015398:Signal Transduction
C117307:KRAS protein, human; D004815:Epidermal Growth Factor; C512478:EGFR protein, human; D066246:ErbB Receptors; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D016283:Proto-Oncogene Proteins p21(ras)