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Description:
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17β -Estradiol induces E2F -1 gene expression in ZR -75 and MCF -7
human breast cancer cells . Analysis of the E2F -1 gene promoter in MCF -7 cells
previously showed that hormone -induced transactivation required interactions
between estrogen receptor α (ERα ) /Sp1 bound to upstream GC -rich sites and
NFYA bound to downstream CCAAT sites within the -169 to -54 promoter
region . This promoter region was also E2 -responsive in ERα -positive ZR -75
cells ; however , further analysis of the promoter showed that cooperative
ERα /Sp1 /NFY interactions were not necessary for hormone -induced
transactivation in ZR -75 cells . The upstream GC -rich motifs are activated
independently by ERα /Sp1 in ZR -75 but not MCF -7 cells , and the downstream
CCAAT sites were also E2 -responsive . E2 also induced reporter gene activity in
ZR -75 cells transfected with an expression plasmid containing the yeast GAL4
DNA binding domain fused to pM -NFYA and a construct containing five tandem
GAL4 response elements . Subsequent studies showed that hormonal activation
of pE2F -1jm1 and pM -NFYA are dependent on non -genomic pathways in which
E2 activates cAMP /protein kinase A . Hormone -dependent regulation of E2F -1
gene expression in ZR -75 and MCF -7 involves different mechanisms ,
demonstrating the importance of cell context on transactivation pathways , even
among ER -positive breast cancer cell lines .
TCDD inhibited ERα -mediated responses in MCF -7 and ZR -75 cells . E2 -
induced E2F -1protein and mRNA levels in MCF -7 and ZR -75 cells and this
response was inhibited by TCDD . Constructs containing GC -rich sites alone or
in combination with the downstream NFY sites were used in transactivation
studies to investigate the mechanism of inhibitory AhR -ERα crosstalk . Although
TCDD inhibited E2 -induced mRNA , protein and reporter gene actitivity , it was
not possible to determine if the inhibitory response was due to limiting ERα
protein levels due to proteasome degradation since proteaome inhibitors alone
blocke hormone -dependent responses . TCDD also inhibited the cAMP /PKA
pathway by inhibiting adenyl cyclase activity . In Drosophila SL -2 cells
cotransfected with the GC -rich -169 to -54 region , ERα and Sp1 plasmids E2
induced transactivation in cells cotransfected with AhR /Arnt expression plasmids
suggesting that the AhR complex suppressed ERα /Sp1 action . These results
demonstrate that TCDD inhibits E2 -dependent activation of both non -genomic
and genomic pathways of ER -mediated E2F -1 gene expression .
17β -Estradiol induces E2F -1 gene expression in ZR -75 and MCF -7
human breast cancer cells . Analysis of the E2F -1 gene promoter in MCF -7 cells
previously showed that hormone -induced transactivation required interactions
between estrogen receptor α (ERα ) /Sp1 bound to upstream GC -rich sites and
NFYA bound to downstream CCAAT sites within the -169 to -54 promoter
region . This promoter region was also E2 -responsive in ERα -positive ZR -75
cells ; however , further analysis of the promoter showed that cooperative
ERα /Sp1 /NFY interactions were not necessary for hormone -induced
transactivation in ZR -75 cells . The upstream GC -rich motifs are activated
independently by ERα /Sp1 in ZR -75 but not MCF -7 cells , and the downstream
CCAAT sites were also E2 -responsive . E2 also induced reporter gene activity in
ZR -75 cells transfected with an expression plasmid containing the yeast GAL4
DNA binding domain fused to pM -NFYA and a construct containing five tandem
GAL4 response elements . Subsequent studies showed that hormonal activation
of pE2F -1jm1 and pM -NFYA are dependent on non -genomic pathways in which
E2 activates cAMP /protein kinase A . Hormone -dependent regulation of E2F -1
gene expression in ZR -75 and MCF -7 involves different mechanisms ,
demonstrating the importance of cell context on transactivation pathways , even
among ER -positive breast cancer cell lines .
TCDD inhibited ERα -mediated responses in MCF -7 and ZR -75 cells . E2 -
induced E2F -1protein and mRNA levels in MCF -7 and ZR -75 cells and this
response was inhibited by TCDD . Constructs containing GC -rich sites alone or
in combination with the downstream NFY sites were used in transactivation
studies to investigate the mechanism of inhibitory AhR -ERα crosstalk . Although
TCDD inhibited E2 -induced mRNA , protein and reporter gene actitivity , it was
not possible to determine if the inhibitory response was due to limiting ERα
protein levels due to proteasome degradation since proteaome inhibitors alone
blocke hormone -dependent responses . TCDD also inhibited the cAMP /PKA
pathway by inhibiting adenyl cyclase activity . In Drosophila SL -2 cells
cotransfected with the GC -rich -169 to -54 region , ERα and Sp1 plasmids E2
induced transactivation in cells cotransfected with AhR /Arnt expression plasmids
suggesting that the AhR complex suppressed ERα /Sp1 action . These results
demonstrate that TCDD inhibits E2 -dependent activation of both non -genomic
and genomic pathways of ER -mediated E2F -1 gene expression . |