A constitutively active form of CREB can activate expression of the rat prolactin promoter in non-pituitary cells.
The pituitary cell-specific transcription factor Pit-1 has been show to trans-activate expression of the prolactin (PRL) promoter in non-pituitary cells. However, the cyclic AMP response element (CRE)-binding protein CREB is known to play a major role in cell-specific expression of hepatocyte-specific genes. Since the PRL promoter contains an asymmetrical form of a cyclic AMP response element (termed the CLE), we investigated whether CREB could also induce PRL promoter activity in non-pituitary cells. Transient expression in rat glial C6 cells of a constitutively active CREB-VP16 fusion protein strongly trans-activated expression of a co-transfected rat PRL promoter construct, (-187)PRL-CAT. Analysis by 5'-deletion showed that this response requires PRL promoter sequences between positions -113/-75. CREB-VP16 did not stimulate expression in C6 cells of any of three control promoter-CAT constructs, implying that the strong response of the PRL promoter to activated CREB is both promoter-specific, and is not due to non-specific transcriptional effects of the potent VP16 moiety of CREB-VP16. Surprisingly, mutations in the CLE only slightly reduced activation by CREB-VP16 of construct (-204)PRL-CAT, implying that the major action of CREB-VP16 on the PRL promoter does not involve a direct interaction with the CLE. CREB-VP16 stimulated PRL-CAT activity in C6 cells as strongly as, and synergistically with, Pit-1. These results imply that CREB can strongly and specifically activate expression of the PRL promoter in non-pituitary cells, via a mechanism different from that employed by Pit-1.
Yan
G
G
Department of Physiology and Biophysics, Mount Sinai School of Medicine, City University of New York, NY 10029, USA.
Chen
X
X
Bancroft
C
C
D000818:Animals; D002460:Cell Line; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D009457:Neuroglia / Q000378:metabolism*; D011388:Prolactin / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics*; D051381:Rats
D017362:Cyclic AMP Response Element-Binding Protein; D011388:Prolactin