Metastasis-inducing dna regulates the expression of the osteopontin gene by binding the transcription factor Tcf-4.
Small 1,000-bp fragments of genomic DNA obtained from human malignant breast cancer cell lines when transfected into a benign rat mammary cell line enhance transcription of the osteopontin gene and thereby cause the cells to metastasize in syngeneic rats. To identify the molecular events underlying this process, transient cotransfections of an osteopontin promoter-reporter construct and fragments of one metastasis-inducing DNA (Met-DNA) have identified the active components in the Met-DNA as the binding sites for the T-cell factor (Tcf) family of transcription factors. Incubation of cell extracts with active DNA fragments containing the sequence CAAAG caused retardation of their mobilities on polyacrylamide gels, and Western blotting identified Tcf-4, beta-catenin, and E-cadherin in the relevant DNA complexes in vitro. Transfection of an expression vector for Tcf-4 inhibited the stimulated activity of the osteopontin promoter-reporter construct caused by transiently transfected active fragments of Met-DNA or permanently transfected Met-DNA. This stimulated activity of the osteopontin promoter-reporter construct is accompanied by an increase in endogenous osteopontin mRNA but not in fos or actin mRNAs in the transfected cells. Permanent transfection of the benign rat mammary cell line with a 20-bp fragment from the Met-DNA containing the Tcf recognition sequence CAAAG caused an enhanced permanent production of endogenous osteopontin protein in vitro and induced the cells to metastasize in syngeneic rats in vivo. The corresponding fragment without the CAAAG sequence was without either effect. Therefore, the regulatory effect of the C9-Met-DNA is exerted, at least in part, by a CAAAG sequence that can sequester the endogenous inhibitory Tcf-4 and thereby promote transcription of osteopontin, the direct effector of metastasis in this system.
El-Tanani
M
M
Cancer and Polio Research Fund Laboratories, Life Sciences Building, School of Biological Sciences, University of Liverpool, Liverpool L69 3BX, United Kingdom.
Barraclough
R
R
Wilkinson
M C
MC
Rudland
P S
PS
D000818:Animals; D001483:Base Sequence; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D004273:DNA, Neoplasm / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D007150:Immunohistochemistry; D009362:Neoplasm Metastasis / Q000235:genetics* / Q000473:pathology; D053495:Osteopontin; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D012795:Sialoglycoproteins / Q000235:genetics* / Q000378:metabolism; D051820:TCF Transcription Factors; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured
D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; D011506:Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; C506895:SPP1 protein, human; D012795:Sialoglycoproteins; C506897:Spp1 protein, rat; D051820:TCF Transcription Factors; C544894:TCF7L2 protein, human; C553059:Tcf7l2 protein, rat; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors; D053495:Osteopontin; D015500:Chloramphenicol O-Acetyltransferase