Human recombinant transforming growth factor alpha stimulates bone resorption and inhibits formation in vitro.

Abstract

Human recombinant transforming growth factor a (TGFa), which binds to the epidermal growth factor (EGF) receptor and causes several biological effects similar to those caused by EGF, was compared with murine EGF for its effects on a number of parameters of bone cell metabolism. TGFa stimulated bone resorption in two organ culture systems, the fetal rat long bone and neonatal mouse calvarial systems. TGFa stimulated bone resorption at concentrations as low as 0.1 ng/ml. TGFa effects on bone resorption in mouse calvariae were inhibited by indomethacin, suggesting that, like EGF, its effects were mediated by prostaglandin synthesis. TGFa had a different time course of action on bone resorption from that of EGF, causing more rapid release of previously incorporated 45Ca from bone cultures, suggesting that TGFa does not function on bone as a simple EGF analogue. TGFa also caused effects on osteoblast function resembling those of EGF. It inhibited alkaline phosphatase activity in cultured rat osteosarcoma cells with the osteoblast phenotype and inhibited collagen synthesis in fetal rat calvaria at concentrations of 1.0 ng/ml. The lowest concentration of TGFa (expressed as nanogram equivalents of EGF per ml) required to produce a response in all of the systems tested was about 1/10th of that needed for EGF to produce a similar effect. These results indicate that TGFa is a potent stimulator of bone resorption and inhibitor of bone formation as assessed by inhibition of collagen synthesis and alkaline phosphatase activity and are consistent with the hypothesis that TGFa may be responsible, at least in part, for the bone resorption associated with some tumors.Transforming growth factor alpha (TGFa) is secreted by a variety of human and rodent tumor cells and binds to the epidermal growth factor (EGF) receptor. TGFa causes many of the known biological effects of EGF (1-3). Multiple peptides of different molecular weights with TGFa activity (as assessed by inhibition of EGF binding and stimulation of anchorage-independent growth) have been detected in culture media and extracts of tumor cells. A small species of 50 amino acids has been purified (4, 5). It is about 40% homologous with EGF (4, 6). Cloning of the cDNA reveals that it is initially synthesized as a larger precursor, which undergoes subsequent posttranslational cleavage. Proper engineering of the sequence coding for the 50 amino acid TGFa has allowed the expression of biologically active human TGFa in Escherichia coli (6).EGF causes osteoclastic bone resorption (7,8) and inhibits bone formation as assessed by collagen synthesis in organ cultures of fetal rat calvariae (7-9) and alkaline phosphatase activity in osteoblast-like cells (10). Since EGF stimulates osteoclastic bone resorption and TGFa competes with EGF for the same receptor, it has been suggested that tumor production of TGFa could be responsible for the bone destruction that is associated with some neoplasms (11,12). Partially purified bone-resorbing activity associated with an animal tumor co...

Epidermal growth factor signalling and bone metastasis

“…Early in vitro studies showed that addition of TGF-a and EGF to bone marrow culture, foetal rat long bone and neonatal mouse calvaria stimulated osteoclast formation and bone resorption (Ibbotson et al, 1986;Lorenzo et al, 1986;Takahashi et al, 1986). Phenotypes from genetically modified mice confirmed the important role of EGF signalling in bone formation.…”

Production and response of a human prostatic cancer line to transforming growth factor-like molecules

“…TGFas have significant sequence and structural homology to EGF and show a variety of biological actions similar to EGF. Their biological activities when assayed in cell culture systems are almost identical (Bascom et al, 1989), although in some cases TGFs are more potent than EGF (Stern et al, 1985;Ibbotson et al, 1986).…”

Breaking down bone: new insight into site-specific mechanisms of breast cancer osteolysis mediated by metalloproteinases: Figure 1.

“…EGFR family members have long been known to stimulate bone resorption (Ibbotson et al 1986;Lorenzo et al 1986;Takahashi et al 1986). Recent investigation showed that the increased osteoclastogenesis is due to alterations of osteoblast-expressed RANKL and OPG (Zhu et al 2007), as osteoclasts do not express EGRF.…”

“…The differential expression of these EGF family members was not regulated at the mRNA level, as assessed by Northern blot analysis, but rather at the post-translational level. Indeed, ADAMTS1 was shown by others to release membrane-bound EGF-like ligands (Liu et al 2006) and Lu et al (2009) showed that MMP-1 could proteolytically cleave AREG, HB-EGF, and TGF-a.EGFR family members have long been known to stimulate bone resorption (Ibbotson et al 1986;Lorenzo et al 1986;Takahashi et al 1986). Recent investigation showed that the increased osteoclastogenesis is due to alterations of osteoblast-expressed RANKL and OPG (Zhu et al 2007), as osteoclasts do not express EGRF.…”