Conditional expression of RET/PTC induces a weak oncogenic drive in thyroid PCCL3 cells and inhibits thyrotropin action at multiple levels.
Chromosomal rearrangements linking the promoter(s) and N-terminal domain of unrelated gene(s) to the C terminus of RET result in constitutively activated chimeric forms of the receptor in thyroid cells (RET/PTC). RET/PTC rearrangements are thought to be tumor-initiating events; however, the early biological consequences of RET/PTC activation are unknown. To explore this, we generated clonal lines derived from well-differentiated rat thyroid PCCL3 cells with doxycycline-inducible expression of either RET/PTC1 or RET/PTC3. As previously shown in other cell types, RET/PTC1 and RET/PTC3 oligomerized and displayed constitutive tyrosine kinase activity. Neither RET/PTC1 nor RET/PTC3 conferred cells with the ability to grow in the absence of TSH, likely because of concomitant stimulation of both DNA synthesis and apoptosis, resulting in no net growth in the cell population. Effects of RET/PTC on DNA synthesis and apoptosis did not require direct interaction of the oncoprotein with either Shc or phospholipase Cgamma. Acute expression of the oncoprotein decreased TSH-mediated growth stimulation due to interference of TSH signaling by RET/PTC at multiple levels. Taken together, these data indicate that RET/PTC is a weak tumor-initiating event and that TSH action is disrupted by this oncoprotein at several points, and also predict that secondary genetic or epigenetic changes are required for clonal expansion.
Wang
Jianwei
J
Division of Endocrinology and Metabolism, University of Cincinnati College of Medicine, Ohio 45267-0547, USA.
Knauf
Jeffrey A
JA
Basu
Saswata
S
Puxeddu
Efisio
E
Kuroda
Hiroaki
H
Santoro
Massimo
M
Fusco
Alfredo
A
Fagin
James A
JA
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics; D002455:Cell Division / Q000187:drug effects / Q000235:genetics; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis; D004318:Doxycycline / Q000494:pharmacology; D009154:Mutation; D056918:Nuclear Receptor Coactivators; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D015514:Oncogene Proteins, Fusion / Q000235:genetics / Q000378:metabolism; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D051096:Proto-Oncogene Proteins c-ret; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D011989:Receptors, Thyrotropin / Q000235:genetics; D015398:Signal Transduction; D013961:Thyroid Gland / Q000166:cytology* / Q000187:drug effects; D013972:Thyrotropin / Q000494:pharmacology*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
C111382:NCOA4 protein, human; D056918:Nuclear Receptor Coactivators; D015513:Oncogene Proteins; D015514:Oncogene Proteins, Fusion; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D011989:Receptors, Thyrotropin; D014157:Transcription Factors; D013972:Thyrotropin; D004247:DNA; D000242:Cyclic AMP; D011505:Protein-Tyrosine Kinases; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases; C495001:Ret protein, rat; C093573:ret-PTC fusion oncoproteins, human; D000262:Adenylyl Cyclases; D004318:Doxycycline