Regulation of c-fos protooncogene expression in human breast cancer cells /
l7β-Estradiol (E2) induces c-fos protooncogene expression in MCF-7 human breast cancer cells. Previous studies in HeLa cells identified an imperfect palindromic estrogen responsive element (ERE) (-1212 to -1200) required for transactivation. In contrast, this ERE was not required for E2-responsivene...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1999.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=730318991&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | l7β-Estradiol (E2) induces c-fos protooncogene expression in MCF-7 human breast cancer cells. Previous studies in HeLa cells identified an imperfect palindromic estrogen responsive element (ERE) (-1212 to -1200) required for transactivation. In contrast, this ERE was not required for E2-responsiveness in MCF-7 cells, and transfection studies showed that a Go-rich motif (-1168 to -1161), which bound Sp1 protein in gel shift assays, was required for E2-inducibility. Both wild-type (wt) ER and HE11 enhanced Sp1-DNA binding and are functional to mediate E2-inducibility. Thus, induction of c-fos gene expression by E2 in MCF-7 cells is dependent on formation of a transcriptionally-active ER/Sp1 complex that binds to a GC-rich enhancer element. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) inhibited the E2-induced c-fos mRNA levels in MCF-7 cells. Transient transfection studies using pFC2-CAT (-1400 to +41) showed that the AhR complex was required for the inhibitory effect of TCDD. The E2-responsive sequence (-1220 to -1155) contains two core dioxin responsive elements (DREs) at -1206 to -1202 and -1163 to -1159. In transient transfection assays, the downstream core DRE (at -1163 to -1159) was identified as a functional inhibitory DRE. The results of photoinduced crosslinking, gel shift and in vitro DNA footprinting assays showed that the AhR complex interacted with the core DRE that also overlapped the E2-responsive GC-rich site (-116t to -1161) suggesting that the mechanism for AhR-mediated antiestrogenicity may be due to quenching or masking at the Sp1 binding site. Growth factors such as EGF, IGF-I and TGF-α stimulate c-fos gene expression in MCF-7 cells. The results suggest that IGF-I activate c-fos gene expression via ER-dependent and -independent pathways, whereas EGF and TGF-α transactivate c-fos gene expression through serum response element (SRE) via MAPK pathway MCF-7 cells. Induction of pSS (-354 to -296) and pSRE (-325 to -296) by E2 was observed using wt ER or HE11 and was inhibited by ICI 182,780. Overexpression of dominant negative Ras and MAPK expression plastics and the MAPKK inhibitor PD 98059 inhibited E2 responsiveness in MCF-7 cells. Gel shift assays showed that E2 enhanced formation of a ternary complex composed of SRF and Elk-1. Thus, this study revealed a novel mechanism of Elk-dependent transactivation through the SRE in the c-fos promoter. |
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| Item Description: | Vita. "Major Subject: Toxicology". |
| Physical Description: | xiii, 226 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 161-225). |