TitleMolecular regulation of insulin-like growth factor binding protein-5 by signaling molecules downstream of the IGF-I receptor in mammary epithelial cells
NameBrandimarto, Jeffrey Alan (author), Cohick, Wendie (chair), Denhardt, David (internal member), Axelrod, David (internal member), Rutgers University, Graduate School - New Brunswick,
SubjectMicrobiology and Molecular Genetics,
Insulin-like growth factor-binding proteins,
DescriptionThe insulin-like growth factor binding proteins (IGFBP) are important regulators of mammary epithelial cell (MEC) growth and can either enhance or inhibit IGF-I action. IGF-I activates the IGF-I receptor (IGF-IR) to initiate two well-characterized signaling pathways; the phosphoinositide 3-kinase pathway (PI3K) and the mitogen activated protein kinase (MAPK) pathway. In the bovine MEC line MAC-T, the PI3K pathway is required for both basal and IGF-I stimulated IGFBP-5 expression. In contrast, inhibition of the MAPK pathway with the chemical inhibitor PD98059 leads to an increase in IGFBP-5 expression in both basal and IGF-I treated conditions. In the present study, we identified molecules downstream of the IGF-IR that might play a role in the inhibitory regulation of IGFBP-5 expression via the MAPK pathway.
The MAPK pathway terminates with the activation of ERK1/2. Activated ERK1/2 enters the nucleus where it affects numerous transcriptional factors. ERK1/2 has been shown to inhibit activation of the peroxisome proliferator-activated receptor gamma (PPARγ). Inhibition of PPARγ with the chemical inhibitor GW9662 led to a decrease in IGFBP-5 message in PD98059-treated MAC-T. Activation of PPARγ and PPARβ/δ via the agonists Rosiglitazone and GW0742, respectively, was found to increase basal IGFBP-5 mRNA expression in murine MEC but not in MAC-T cells.
While PPARγ contributed to the PD98059-stimulated increase in IGFBP-5 message, it was unable to account for the total increase. We therefore examined the promoter region of IGFBP-5 to identify factors that could be affected by mitogens. Both mouse and human IGFBP-5 promoters contain a consensus NFκB binding site. In the present study, phenethyl caffeiate, an inhibitor of NFκB, almost completely inhibited the increase in IGFBP-5 observed with PD98059 and IGF-I + PD98059-stimulated IGFBP-5 mRNA and protein expression in MAC-T cells. Interestingly, IGFBP-3 expression was inversely regulated by phenethyl caffeiate.
In conclusion the synergistic increase in IGFBP-5 expression observed with IGF-I and inhibition of the MAPK pathway may be due to the formation of a PPARγ NFκB complex that binds to the promoter region of IGFBP-5. Rapid ERK dephosphorylation has been reported in involution, therefore this regulation may be important in inducing IGFBP-5 during involution in the bovine mammary gland.
NoteIncludes bibliographical references (p. 51-61)
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
RightsThe author owns the copyright to this work.