A canonical nerve growth factor-induced gene-B response element appears not to be involved in the cyclic adenosine monophosphate-dependent expression of differentiation in thyrocytes.
The expression of transcriptionally active nerve growth factor-induced gene-B (NGFI-B) is rapidly induced in thyroid follicular cells in response to cAMP stimulation. As the transcription of thyrocyte-specific genes is controlled by the cAMP cascade, we have investigated a possible involvement of NGFI-B in this control. Recombinant adenoviruses driving the expression of either the intact NGFI-B protein or a truncated form of it that lacks the capacity to transactivate a NBRE-dependent promoter, were used to infect dog thyrocytes maintained in primary culture. Northern blot analysis of total RNA from infected cells revealed that the expression of NGFI-B was not sufficient to induce a significant accumulation of specific transcripts (thyroglobulin, thyroperoxidase, sodium-iodide symporter) in unstimulated thyrocytes. The overproduction of the transcriptionally inactive form of NGFI-B in thyrocytes maintained in the presence of forskolin after infection did not impair the accumulation of the thyroid-specific transcripts. These data show that NGFI-B does not control the expression of differentiation in thyrocytes by acting through a canonical NBRE. As a consequence, we must consider that either the expression of NGFI-B in cAMP-stimulated thyrocytes is not critically linked to the expression of differentiation or that NGFI-B is implicated in a regulatory mechanism which differs from its known action at the level of a NBRE.
Pichon
B
B
I.R.I.B.H.N., Faculté de Médecine, U.L.B., Bruxelles, Belgium.
Vassart
G
G
Christophe
D
D
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000494:pharmacology; D004274:DNA, Recombinant; D004268:DNA-Binding Proteins / Q000235:genetics; D004285:Dogs; D017353:Gene Deletion; D015870:Gene Expression; D005786:Gene Expression Regulation / Q000187:drug effects*; D020932:Nerve Growth Factor / Q000235:genetics*; D057105:Nuclear Receptor Subfamily 4, Group A, Member 1; D010544:Peroxidases / Q000235:genetics; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D020218:Response Elements; D013954:Thyroglobulin / Q000235:genetics; D013961:Thyroid Gland / Q000166:cytology* / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects; D014161:Transduction, Genetic; D014162:Transfection
D004274:DNA, Recombinant; D004268:DNA-Binding Proteins; D057105:Nuclear Receptor Subfamily 4, Group A, Member 1; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D014157:Transcription Factors; D013954:Thyroglobulin; D020932:Nerve Growth Factor; D000242:Cyclic AMP; D010544:Peroxidases