Mammary gland development requires syndecan-1 to create a beta-catenin/TCF-responsive mammary epithelial subpopulation.
Mice with a null mutation in the cell surface heparan sulfate (HS) proteoglycan, syndecan-1 (Sdc1), develop almost normally, but resist mammary tumor development in response to Wnt-1. Here, we test the hypothesis that Sdc1 promotes Wnt-1-induced tumor development by interacting with the Wnt cell surface signaling complex. Thus, the response of Sdc1-/- mammary epithelial cells (mecs) to the intracellular, activated Wnt signal transducer, DeltaNbeta-catenin, was assayed both in vitro and in vivo, to test whether beta-catenin/TCF transactivation was Sdc1-independent. Surprisingly, we found that the expression of a canonical Wnt pathway reporter, TOP-FLASH, was reduced by 50% in both unstimulated Sdc1-/- mecs and in stimulated cells responding to Wnt1 or DeltaNbeta-catenin. Tumor development in response to DeltaNbeta-catenin was also significantly delayed on a Sdc1-/- background. Furthermore, the average beta-catenin/TCF transactivation per cell was normal in Sdc1-/- mec cultures, but the number of responsive cells was reduced by 50%. Sdc1-/- mecs show compensatory changes that maintain the number of HS chains, hence these experiments cannot test the coreceptor activity of HS for Wnt signaling. We propose that TCF-dependent transactivational activity is suppressed in 50% of cells in Sdc1-/- glands, and conclude that the major effect of Sdc1 does not map to the activity of the Wnt signaling complex, but to another pathway to create or stabilize the beta-catenin/TCF-responsive tumor precursor cells in mouse mammary gland.
Liu
Bob Y
BY
McArdle Laboratory for Cancer Research, University of Wisconsin Medical School, 1400 University Ave, Madison, WI, USA.
Kim
Young Chul
YC
Leatherberry
Vicki
V
Cowin
Pam
P
Alexander
Caroline M
CM
D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D004848:Epithelium / Q000378:metabolism*; D005260:Female; D005434:Flow Cytometry; D005838:Genotype; D049452:Green Fluorescent Proteins; D008156:Luciferases / Q000378:metabolism; D008164:Luminescent Proteins / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000166:cytology / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008957:Models, Genetic; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011509:Proteoglycans / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D015398:Signal Transduction; D053668:Syndecan-1; D053667:Syndecans; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D051153:Wnt Proteins; D051155:Wnt1 Protein; D029961:Zebrafish Proteins; D051176:beta Catenin
C495267:CTNNB1 protein, mouse; D003598:Cytoskeletal Proteins; D008164:Luminescent Proteins; D008562:Membrane Glycoproteins; D011509:Proteoglycans; D011518:Proto-Oncogene Proteins; C508242:Sdc1 protein, mouse; D053668:Syndecan-1; D053667:Syndecans; D015534:Trans-Activators; D051153:Wnt Proteins; D051155:Wnt1 Protein; C495246:Wnt1 protein, mouse; D029961:Zebrafish Proteins; D051176:beta Catenin; D049452:Green Fluorescent Proteins; D008156:Luciferases