title: Latent transforming growth factor beta1 activation in situ: quantitative and functional evidence after low-dose gamma-irradiation.
abstract: The biological activity of transforming growth factor beta1 (TGF-beta) is controlled by its secretion as a latent complex in which it is noncovalently associated with latency-associated peptide (LAP). Activation is the extracellular process in which TGF-beta is released from LAP, and is considered to be a primary regulatory control. We recently reported rapid and persistent changes in TGF-beta immunoreactivity in conjunction with extracellular matrix remodeling in gamma-irradiated mouse mammary gland. Our hypothesis is that these specific changes in immunoreactivity are indicative of latent TGF-beta activation. In the present study, we determined the radiation dose response and tested whether a functional relationship exists between radiation-induced TGF-beta and collagen type III remodeling. After radiation exposures as low as 0.1 Gy, we detected increased TGF-beta immunoreactivity in the mammary epithelium concomitant with decreased LAP immunostaining, which are events consistent with activation. Quantitative image analysis demonstrated a significant (P=0.0005) response at 0.1 Gy without an apparent threshold and a linear dose response to 5 Gy. However, in the adipose stroma, loss of LAP demonstrated a qualitative threshold at 0.5 Gy. Loss of LAP paralleled induction of collagen III immunoreactivity in this tissue compartment. We tested whether TGF-beta mediates collagen III expression by treating animals with TGF-beta panspecific monoclonal antibody, 1D11.16, administered i.p. shortly before irradiation. Radiation-induced collagen III staining in the adipose stroma was blocked in an antibody dose-dependent manner, which persisted through 7 days postirradiation. RNase protection assay revealed that radiation-induced elevation of total gland collagen III mRNA was also blocked by neutralizing antibody treatment. These data provide functional confirmation of the hypothesis that radiation exposure leads to latent TGF-beta activation, support our interpretation of the reciprocal shift in immunoreactivity as evidence of activation, and implicate TGF-beta as a mediator of tissue response to ionizing radiation. The sensitivity of activation to low radiation doses points to a potential role for TGF-beta in orchestrating tissue response to oxidative stress. As such, radiation may be useful as a probe to delineate the consequences of latent TGF-beta activation in situ.
authors.affiliation: Radiological Health Sciences, Colorado State University, Ft. Collins 80523, USA.
authors.forename: E J
authors.initials: EJ
authors.lastname: Ehrhart
authors.forename: P
authors.initials: P
authors.lastname: Segarini
authors.forename: M L
authors.initials: ML
authors.lastname: Tsang
authors.forename: A G
authors.initials: AG
authors.lastname: Carroll
authors.forename: M H
authors.initials: MH
authors.lastname: Barcellos-Hoff
mesh_terms: D000818:Animals; D003037:Cobalt Radioisotopes; D003094:Collagen / Q000096:biosynthesis / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D004848:Epithelium / Q000378:metabolism / Q000528:radiation effects; D005260:Female; D005720:Gamma Rays; D008321:Mammary Glands, Animal / Q000378:metabolism / Q000528:radiation effects*; D051379:Mice; D008807:Mice, Inbred BALB C; D010446:Peptide Fragments; D011498:Protein Precursors; D011506:Proteins / Q000378:metabolism / Q000528:radiation effects*; D016212:Transforming Growth Factor beta / Q000096:biosynthesis / Q000528:radiation effects*; D053773:Transforming Growth Factor beta1
chemical_list: D003037:Cobalt Radioisotopes; D010446:Peptide Fragments; D011498:Protein Precursors; D011506:Proteins; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D003094:Collagen