|Authors||Chen H, Carson-Walter EB, Baylin SB, Nelkin BD, Ball DW|
|Journal||Surgery Volume: 120 Issue: 2 Pages: 168-72; discussion 173|
|Publish Date||1996 Aug|
Human achaete-scute homolog-1 (hASH1), a fetal neural transcription factor, is highly expressed in neuroendocrine tumors such as medullary thyroid cancer (MTC). Although hASH1 probably plays a part in the growth and development of these tumors, its precise role and mechanism are unknown.To further elucidate the function and regulation of hASH1 in neuroendocrine tumor differentiation, we used a model of MTC tumor differentiation mediated by the ras/raf-1 signaling pathway. The MTC TT cells alone or transduced with a beta-estradiol activatable raf-1 construct (TT: delta Raf-1:ER) were treated with beta-estradiol or carrier. Northern analysis and nuclear run-off assays were performed to determine the hASH1 messenger RNA (mRNA) levels and transcription rate, respectively.The TT: delta Raf-1:ER cells treated with beta-estradiol underwent marked biochemical and morphologic changes, including cell rounding, increase in calcitonin transcription, loss of RET proto-oncogene expression, and cessation of cell growth. During this differentiation process expression of hASH1 mRNA was silenced. Nuclear run-off experiments revealed that this decrease in steady-state hASH1 mRNA by raf-1 activation resulted predominantly from transcriptional inhibition.Silencing of hASH1 in parallel with loss of RET is associated with development of a mature C-cell differentiation pattern. Mechanisms leading to transcriptional silencing of hASH1 may be crucial in regulating the proliferative capacity or differentiation status of MTC. Downstream targets of hASH1 could play a role in C-cell proliferation and progression to MTC.