Activation of the ras/raf-1 signal transduction pathway in carcinoid tumor cells results in morphologic transdifferentiation.
BACKGROUND
Recent studies of neuroendocrine tumor cell lines suggest that ras/raf-1 activation could be detrimental to tumorigenesis. The mechanism by which it alters neuroendocrine tumor cells is unclear. We hypothesize that activation of the ras/raf signal transduction pathway may alter gastrointestinal carcinoid cells by inducing morphologic transdifferentiation.


METHODS
Pancreatic carcinoid (BON) cells were transduced in a stable manner with an estrogen inducible raf-1 fusion protein (creating "BON-raf cells"). BON and BON-raf cells were then treated with either control or 1 micromol/L estradiol (E2). Western blots were used to confirm the phosphorylation of extracellular signal-regulated kinase 1/2. Morphologic changes were evaluated using light and electron microscopy.


RESULTS
Western blots using antibodies against phosphorylated and unphosphorylated extracellular signal-regulated kinase 1/2. confirmed that phosphorylation was only present in the BON-raf E2 cells. BON cells treated with control and E2 and BON-raf cells treated with control all looked identical in culture. After treatment with E2 to induce raf-1, the BON-raf cells underwent dramatic morphologic changes. Under light and electron microscopy the cells became flatter and developed much sharper cellular borders mimicking cellular differentiation.


CONCLUSIONS
Activation of the ras/raf-1 signal transduction pathway leads to prominent phenotypic changes that resemble differentiation of gastrointestinal carcinoid cells in vitro.
Sippel
Rebecca S
RS
Department of Surgery, The University of Wisconsin Medical School, H4/750 Clinical Science Center, 600 Highland Avenue, Madison, WI 53792, USA.
Chen
Herbert
H
D002276:Carcinoid Tumor; D002454:Cell Differentiation; D006801:Humans; D020935:MAP Kinase Signaling System / Q000502:physiology*; D008854:Microscopy, Electron; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010190:Pancreatic Neoplasms; D010766:Phosphorylation; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000378:metabolism / Q000648:ultrastructure; D018631:ras Proteins / Q000378:metabolism*
D019908:Proto-Oncogene Proteins c-raf; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D018631:ras Proteins