Autocrine mechanisms of action of insulin-like growth factor-I (IGF-I) and hormonal regulation of expression of IGF-finding proteins in mammary epithelial cells

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dc.contributor.authorRomagnolo, Donatoen
dc.contributor.committeechairAkers, Robert Michaelen
dc.contributor.committeememberWong, Eric A.en
dc.contributor.committeememberGwazdauskas, Francisen
dc.contributor.committeememberJohnson, J.L.en
dc.contributor.committeememberTurner, J.D.en
dc.contributor.committeememberVinson, William E.en
dc.contributor.departmentAnimal Scienceen
dc.date.accessioned2014-03-14T21:14:32Zen
dc.date.adate2008-06-06en
dc.date.available2014-03-14T21:14:32Zen
dc.date.issued1993en
dc.date.rdate2008-06-06en
dc.date.sdate2008-06-06en
dc.description.abstractLimited information is available concerning the molecular and cellular mechanisms that regulate expression of insulin-like growth factor-I (IGF-I) and IGF-binding proteins (IGFBPs) genes in mammary epithelial cells. To test the hypothesis that IGF-I affects growth of bovine mammary epithelial cells through an autocrine and/or paracrine pathway, several cell lines were developed expressing an ovine exon-2 containing IGF-I cDNA under the control of the mouse mammary tumor virus-long terminal repeat (pMMTV-IGF-I), early simian virus (pSV40-IGF-I), and herpes simplex thymidine kinase (pTK-IGF-I) promoters. Stably transfected clones were generated by cotransfection of clonal MAC-T cells with the IGF-I expression vectors and a plasmid conferring resistance to hygromycin-B (HYG-B), using a calcium phosphate precipitation procedure. Induction of the MMTV-LTR with the glucocorticoid dexamethasone (DEX) was required for enhanced expression of IGF-I in MD-IGF-I (MD=Mammary Derived) cells, whereas SV40-IGF-I cells constitutively expressed the highest levels of IGF-I, followed by TK-IGF-I cells. Activity of the MMTV promoter in MD-IGF-I cells was coordinately regulated by lactogenic hormones and extracellular matrix. Acute secretion of DEX-induced recombinant IGF-I by MD-IGF-I cells stimulated cell proliferation through an autocrine/paracrine pathway and triggered the expression of IGFBP-3. Neither acute nor constitutive expression of IGF-I affected expression of type 1 IGF receptor mRNAs, but down-regulated cell surface receptor levels, in the order SV40-> TK- > MD-IGF-I. Secretion of IGF-I-induced IGFBP-3 potentiated the mitogenic actions of IGF-I as evidenced by enhancement of [³H]thymidine uptake into DNA of parental MAC-T cells. This study provides evidence that local production of IGF-I can stimulate cell proliferation of bovine mammary epithelial cells through an autocrine/paracrine mode of action. We suggest that secretion of IGF-I-induced IGFBP-3 by bovine mammary epithelial cells enhances cell responsiveness to IGF-I, but does not prevent down-regulation of the IGF-I receptor in cells constitutively expressing IGF-I.en
dc.description.degreePh. D.en
dc.format.extentxi, 206 leavesen
dc.format.mediumBTDen
dc.format.mimetypeapplication/pdfen
dc.identifier.otheretd-06062008-171517en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-06062008-171517/en
dc.identifier.urihttp://hdl.handle.net/10919/38476en
dc.language.isoenen
dc.publisherVirginia Techen
dc.relation.haspartLD5655.V856_1993.R652.pdfen
dc.relation.isformatofOCLC# 29179597en
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subject.lccLD5655.V856 1993.R652en
dc.subject.lcshAutocrine mechanismsen
dc.subject.lcshCellular control mechanismsen
dc.subject.lcshEpithelial cellsen
dc.subject.lcshInsulin-like growth factor-binding proteinsen
dc.titleAutocrine mechanisms of action of insulin-like growth factor-I (IGF-I) and hormonal regulation of expression of IGF-finding proteins in mammary epithelial cellsen
dc.typeDissertationen
dc.type.dcmitypeTexten
thesis.degree.disciplineAnimal Scienceen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.namePh. D.en

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