A Pit-1 phosphorylation mutant can mediate both basal and induced prolactin and growth hormone promoter activity.
The transcription factor Pit-1 has been shown to be important for both the developmental and homeostatic regulation of expression of the PRL and GH genes in pituitary cells. However, little is known about possible covalent modifications in Pit-1 that might mediate its transactivational properties. Previous studies showing that Pit-1 is a phosphorylation substrate for either protein kinase A or C, or their cellular inducers, led us to investigate whether phosphorylation of Pit-1 is required for its function in either basal or induced cellular activity of either the PRL or GH promoters. The transactivational properties of wild type Pit-1 were compared with those of Pit-1(A3), mutated in the three known phosphorylation sites. At saturating levels of Pit-1 expression vectors, activation of transient basal expression in HeLa cells of constructs (-1957)PRL-CAT or (-244)GH-CAT by RSV-Pit-1(A3) was, respectively, about 50% and 65% as strong as by RSV-Pit-1. Hence, phosphorylation at the sites mutated in Pit-1(A3) is not critically required for basal transactivation of either promoter but may modulate this activity. RSV-Pit-1 and RSV-Pit-1(A3) were equally effective in mediating estrogen receptor stimulation of (-1957)PRL-CAT expression in HeLa cells, thus revealing no phosphorylation requirement for the prerequisite for Pit-1 in estrogen receptor action on the PRL estrogen response element.(ABSTRACT TRUNCATED AT 250 WORDS)
Fischberg
D J
DJ
Department of Physiology and Biophysics, Mount Sinai School of Medicine, City University of New York, New York 10029.
Chen
X H
XH
Bancroft
C
C
D000818:Animals; D001483:Base Sequence; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004742:Enhancer Elements, Genetic / Q000502:physiology; D005809:Genes, Regulator / Q000235:genetics* / Q000502:physiology*; D013006:Growth Hormone / Q000096:biosynthesis / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010903:Pituitary Gland, Anterior; D017354:Point Mutation / Q000235:genetics; D011388:Prolactin / Q000096:biosynthesis / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000502:physiology*; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D011960:Receptors, Estrogen / Q000502:physiology; D050817:Transcription Factor Pit-1; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; C494187:POU1F1 protein, human; C494186:Pou1f1 protein, rat; D011960:Receptors, Estrogen; D050817:Transcription Factor Pit-1; D014157:Transcription Factors; D011388:Prolactin; D013006:Growth Hormone; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C