The role of human achaete-scute homolog-1 in medullary thyroid cancer cells.
BACKGROUND
Human achaete-scute homolog-1 (hASH1) is a transcription factor that is expressed highly in neuroendocrine tumors such as medullary thyroid cancer (MTC). Thyroid C-cells do not develop in hASH1 knockout mice, which suggests that hASH1 is essential for normal C-cell development.


METHODS
To determine the effect of raf-1 induction on hASH1 and hormone production, we used an estrogen inducible raf-1 construct in MTC cell line (TT) cells (TT-raf cells). TT or TT-raf cells were treated with control or 1 microM estradiol. After 48 hours, the cells were analyzed for levels of hASH1 and chromogranin A by Western blotting and for calcitonin production by enzyme-linked immunosorbent assay.


RESULTS
Activation of raf-1 in the TT-raf cells resulted in high levels of phosphorylated MEK and ERK1/2, a morphologic transdifferentiation, and a decrease in chromogranin A and calcitonin levels that are associated with a reduction in hASH1 production. Furthermore, using MEK inhibitors, we demonstrated that these raf-1-mediated changes are dependent on MEK but not ERK1/2 activation.


CONCLUSIONS
hASH1 down-regulation by raf-1 in MTC cells is associated with a significant decrease in hormone production. Thus, hASH1 appears to be important in the endocrine phenotype of MTC tumors and may serve as a molecular target for the treatment of patients with MTC.
Sippel
Rebecca S
RS
Department of Surgery, The University of Wisconsin Medical School and the University of Wisconsin Comprehensive Cancer Center, 600 Highland Avenue, Madison, WI 53792, USA.
Carpenter
Jennifer E
JE
Kunnimalaiyaan
Muthusamy
M
Chen
Herbert
H
D051792:Basic Helix-Loop-Helix Proteins; D002116:Calcitonin / Q000378:metabolism; D018276:Carcinoma, Medullary / Q000378:metabolism* / Q000473:pathology; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000502:physiology*; D015536:Down-Regulation; D006801:Humans; D010641:Phenotype; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D013964:Thyroid Neoplasms / Q000378:metabolism* / Q000473:pathology; D014157:Transcription Factors / Q000502:physiology*
D051792:Basic Helix-Loop-Helix Proteins; D002116:Calcitonin; D004268:DNA-Binding Proteins; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D014157:Transcription Factors; C065500:ASCL1 protein, human