On the Transforming Growth Factor β-Like Activity of Synthetic Polypeptides Comprising the Amino-Terminal Sequence of Human Parathyroid Hormone-Related Peptide

Abstract

Purified native forms of human parathyroid hormone-related peptide (PTHrp) have recently been reported to display biological activities characteristic of transforming growth factor beta (TGF-beta). The TGF-beta-like property of PTHrp may reside within the amino N-terminal PTH-receptor binding region of the polypeptide, since a synthetic analog corresponding to amino acids 1-36 of human PTHrp is as active as purified native PTHrp in bioassays specific to TGF-beta. Complete lack of structural similarity between PTHrp and TGF-beta prompted us to address the question whether copresence of the TGF-beta-like and PTH-like biological activities in the N-terminal sequence of the PTHrp molecule is a general phenomenon observable with different N-terminal PTHrp peptides of varying amino acid chain length in a variety of target cells that respond in defined ways to TGF-beta in vitro. Two forms of synthetic N-terminal human PTHrp, PTHrp-(1-34) and [Tyr40]PTHrp-(1-40), which are fully active in conventional assays for PTH/PTHrp, were tested for effects in three in vitro bioassay systems for TGF-beta: 1) stimulation, and 2) inhibition, respectively, of epidermal growth factor-dependent soft-agar colony formation of either normal rat kidney-derived fibroblasts (NRK 49F) or human lung carcinoma cells (A549); and 3) biosynthesis of metabolically labeled fibronectin in both NRK 49F cells and clonal osteoblastic rat osteosarcoma cells (ROS 17/2.8). Human TGF-beta over the dose range of 2.5-80 pM significantly stimulated or inhibited soft-agar colony formation of either NRK 49F or A549 cells, respectively, and caused a severalfold increase in biosynthetically labeled [35S]fibronectin in NRK 49F and ROS 17/2.8 cells. In contrast, none of PTHrp-(1-34), [Tyr40]PTHrp-(1-40), and synthetic human PTH-(1-34), each tested at 0.1-10 nM, displayed detectable biological activity in any of the three assay systems. In addition, covalent cross-linking of intact NRK 49F and ROS 17/2.8 cells with either [125I]TGF-beta or 125I-[Tyr40] PTHrp-(1-40) revealed the presence of several distinct affinity-labeled receptor species for TGF-beta in both cell types and the 80K PTH/PTHrp receptors in ROS 17/2.8 cells. The affinity-labeled TGF-beta receptor species were insensitive to excess PTHrp and PTH peptides, and the 80K PTH/PTHrp receptors were insensitive to excess TGF-beta, indicating that PTHrp and TGF-beta do not cross-react with respect to receptor binding for interaction with these cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Parathyroid hormone-related protein ameliorates death receptor-mediated apoptosis in lung cancer cells

“…PTHrP might contribute to cancer progression by stimulating cancer cell growth and/or inhibiting apoptosis. PTHrP-(1-34) is a growth stimulant in many malignant cell lines, including human lung cancer cells (4,19), and it inhibits apoptosis in various cells, including growth plate chondrocytes, pancreatic ␤-cells, LNCaP prostate carcinoma cells, MCF-7 breast carcinoma cells, cerebellar neurons, cytotrophoblasts, and coronary endothelial cells (5,8,14,26,29). The effects of PTHrP on lung cancer cell apoptosis are unknown.…”