Tc. Ganguly et al., REGULATION OF THE RAT-LIVER SODIUM-DEPENDENT BILE-ACID COTRANSPORTER GENE BY PROLACTIN - MEDIATION OF TRANSCRIPTIONAL ACTIVATION BY STAT5, The Journal of clinical investigation, 99(12), 1997, pp. 2906-2914
The intracellular mechanism(s) underlying the upregulation of the hepa
tic Na+/taurocholate cotransporting polypeptide (ntcp) by prolactin (P
RL) are unknown. In this report, we demonstrate a time-dependent incre
ase in nuclear translocation of phosphorylated liver Stat5 (a member o
f the Signal Transducers and Activators of Transcription family) that
correlated with suckling-induced increases in serum PRL levels. In ele
ctrophoretic mobility gel shift assays, nuclear Stat5 exhibited specif
ic DNA-binding ability towards IFN-gamma-activated sequence (GAS)-like
elements (GLEs; 5'-TTC/A-PyNPu-G/TAA-3') located in the -937 to -904
bp region of the ntcp promoter. Transient cotransfections in HepG2 cel
ls revealed that PRL inducibility (2.5-3-fold) required coexpression o
f the long form of the PRL receptor (PRLRL and Stat5. Deletion analysi
s mapped the PRL-inducible region to -1237 to -758 bp of the ntcp prom
oter. Linking this 0.5-kb region to a heterologous thymidine kinase (t
k) promoter, or linking multimerized ntcp GLEs either upstream of the
ntcp minimal promoter (-158 to +47 bp) or the heterologous promoter co
nferred dose-dependent PRL responsiveness. The short form of the PRL r
eceptor failed to transactivate ntcp GLEs. These results indicate that
PRL acts via the PRLRL to facilitate Stat5 binding to ntcp-GLEs and t
o transcriptionally regulate ntcp.