v-erbA overexpression is required to extinguish c-erbA function in erythroid cell differentiation and regulation of the erbA target gene CAII.
The v-erbA oncoprotein represents a retrovirus-transduced oncogenic version of the thyroid hormone (T3/T4) receptor c-erbA (type alpha). It contributes to virus-induced erythroleukemia by efficiently arresting differentiation of red cell progenitors and by suppressing transcription of erythrocyte-specific genes. Here, we show that v-erbA and c-erbA bind directly to sequences within the promoter of the erythrocyte-specific carbonic anhydrase II (CAII), a gene whose transcription is efficiently suppressed by v-erbA. This erbA-binding site confers thyroid hormone responsiveness to a heterologous promoter in transient expression experiments and is a target for efficient down-regulation of CAII transcription by the v-erbA oncoprotein. In stably transformed erythroblasts coexpressing the v-erbA oncoprotein and the c-erbA/T3 receptor at an approximately equimolar ratio, c-erbA activity is dominant over v-erbA. T3 efficiently induced erythroid differentiation in these cells, thus overcoming the v-erbA-mediated differentiation arrest. Likewise, T3 activated CAII transcription as well as transient expression of a T3-responsive reporter gene containing the CAII-specific erbA-binding site. The c-erbA-dependent activation of this CAII reporter construct could only be suppressed by very high amounts of v-erbA. Our results suggest that overexpression of v-erbA is required for its function as an oncoprotein.
Disela
C
C
Institute for Molecular Pathology, Wien, Austria.
Glineur
C
C
Bugge
T
T
Sap
J
J
Stengl
G
G
Dodgson
J
J
Stunnenberg
H
H
Beug
H
H
Zenke
M
M
D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D015152:Blotting, Northern; D002256:Carbonic Anhydrases / Q000235:genetics*; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics*; D002461:Cell Line, Transformed; D004351:Drug Resistance / Q000235:genetics; D004900:Erythroblasts / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D005786:Gene Expression Regulation / Q000235:genetics*; D015750:Genes, gag / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D008156:Luciferases / Q000235:genetics; D008969:Molecular Sequence Data; D009355:Neomycin / Q000494:pharmacology; D018774:Oncogene Proteins v-erbA; D010957:Plasmids / Q000235:genetics; D011233:Precipitin Tests; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D011988:Receptors, Thyroid Hormone / Q000235:genetics; D015682:Retroviridae Proteins, Oncogenic / Q000235:genetics*; D014284:Triiodothyronine / Q000494:pharmacology; D014616:Vaccinia virus / Q000235:genetics
D018774:Oncogene Proteins v-erbA; D011518:Proto-Oncogene Proteins; D011988:Receptors, Thyroid Hormone; D015682:Retroviridae Proteins, Oncogenic; D014284:Triiodothyronine; D008156:Luciferases; D002256:Carbonic Anhydrases; D009355:Neomycin