Quantitation of TGF-β proteins in mouse tissues shows reciprocal changes in TGF-β1 and TGF-β3 in normal vs neoplastic mammary epithelium

Transforming growth factor-beta s (TGF-beta s) regulate tissue homeostasis, and their expression is perturbed in many diseases. The three isoforms (TGF-beta 1, -beta 2, and -beta 3) have similar bioactivities in vitro but show distinct activities in vivo. Little quantitative information exists for expression of TGF-beta isoform proteins in physiology or disease. We developed an optimized method to quantitate protein levels of the three isoforms, using a Luminex (R) xMAP (R)-based multianalyte assay following acid-ethanol extraction of tissues. Analysis of multiple tissues and plasma from four strains of adult mice showed that TGF-beta 1 is the predominant isoform with TGF-beta 2 being similar to 10-fold lower. There were no sex-specific differences in isoform expression, but some tissues showed inter-strain variation, particularly for TGF-beta 2. The only adult tissue expressing appreciable TGF-beta 3 was the mammary gland, where its levels were comparable to TGF-beta 1. In situ hybridization showed the luminal epithelium as the major source of all TGF-beta isoforms in the normal mammary gland. TGF-beta 1 protein was 3-8-fold higher in three murine mammary tumor models than in normal mammary gland, while TGF-beta 3 protein was 2-3-fold lower in tumors than normal tissue, suggesting reciprocal regulation of these isoforms in mammary tumorigenesis.