Domain-specific Mutations of a Transforming Growth Factor (TGF)-β1 Latency-associated Peptide Cause Camurati-Engelmann Disease Because of the Formation of a Constitutively Active Form of TGF-β1

Abstract

Transforming growth factor (TGF)-␤1 is secreted as a latent form, which consists of its mature form and a latency-associated peptide (␤1-LAP) in either the presence or the absence of additional latent TGF-␤1-binding protein. We recently reported that three different missense mutations (R218H, R218C, and C225R) of ␤1-LAP cause the Camurati-Engelmann disease (CED), an autosomal dominant disorder characterized by hyperosteosis and sclerosis of the diaphysis of the long bones. Pulse-chase experiments using fibroblasts from CED patients and expression experiments of the mutant genes in an insect cell system suggest that these mutations disrupt the association of ␤1-LAP and TGF-␤1 and the subsequent release of the mature TGF-␤1. Furthermore, the cell growth of fibroblasts from a CED patient and mutant gene-transfected fibroblasts was suppressed via TGF-␤1. The growth suppression observed was attenuated by neutralizing antibody to TGF-␤1 or by treatment of dexamethasone. On the other hand, the proliferation of human osteoblastic MG-63 cells was accelerated by coculture with CED fibroblasts. These data suggest that the domain-specific mutations of ␤1-LAP result in a more facile activation of TGF-␤1, thus causing CED. Transforming growth factor-␤1 (TGF-␤1)1 is a multifunctional protein acting on cell growth, differentiation, and morphogenesis of many different-type cells. In skeletal tissue, TGF-␤1 serves as a systematic regulator that couples bone formation and resorption by regulating the function of the osteoblasts and osteoclasts (1-5).The mature form of TGF-␤1 is proteolytically cleaved from the N-terminal remnant of the TGF-␤1 precursor, designated as TGF-␤1 latency-associated peptide (␤1-LAP) but remains non-covalently associated with the rest of the complex, which plays a role in latency of TGF-␤1 (6). TGF-␤1 is ubiquitously distributed, and the activation of the latent form is likely an important step, because it exists as either a large latent form, composed of ␤1-LAP, TGF-␤1, and latent TGF-␤1-binding protein (LTBP), or a small latent form, which is devoid of LTBP (7). Under normal conditions, activation of the latent TGF-␤1 is strictly controlled as follows. The large latent form is temporarily converted to the small latent form, which is then cleaved by plasmin or the plasmin-like protease to give the mature TGF-␤1 (6, 8, 9).Camurati-Engelmann disease (CED) or progressive diaphyseal dysplasia (DPD1) is an autosomal dominant disorder that is characterized by hyperosteosis and sclerosis of the diaphysis of the long bones (10). The onset of CED is often during early childhood with severe pain in the legs, muscle weakness, a waddling gait, and easy fatigability. The patients occasionally suffer from systemic manifestations, such as anemia, leukopenia, or hepatosplenomegaly (11). We, as well as two other groups, previously assigned the locus for CED to chromosome 19q13. 1-q13.3 (12-14). By a positional candidate gene approach and haplotype analyses, three different missense mutations (R218H, R218C, and C225R), wh...

TGF-β Family Signaling in Connective Tissue and Skeletal Diseases

“…Clinical manifestations do not include fibrosis or aneurysm, and no evidence for increased TGF-b signaling has been described in the aortic wall or other tissues, suggesting that these mutations have tissue-specific effects on TGF-b activity. It appears that patients with CED have increased rates of bone resorption as well as bone formation, with the overall balance shifted toward bone formation, possibly because of increased proliferation of osteoblasts (Hernandez et al 1997;Saito et al 2001;McGowan et al 2003). CED can be successfully treated with glucocorticosteroids, which decrease proliferation, maturation and ECM synthesis in osteoblasts and osteocytes, and also increase the rate of apoptosis of these cells, thus resulting in a net decrease in bone mass (Low et al 1985;Naveh et al 1985).…”

Medical Applications of Transforming Growth Factor-

“…Patients with CamuratiEngelmann have a missense mutation in the latency associated peptide which changes one of three different amino acids, producing constitutively active TGF-β. 12,42 This results in disregulation of TGF-β synthesis, uncoupling bone formation and resorption at the level of the osteoblasts and osteoclasts.…”

“…Mutations preventing TGF-β function are also causal for hereditary hemorrhagic telangiectasia, 10 and corneal dystrophy. 11 Over activity of TGF-β leads to Camurati-Engelmann Disease of bone, 12 glomerulonephritis, 13 scar formation, 14 keloids, 15 pulmonary fibrosis, 16 and liver cirrhosis. 17 The TGF-β proteins are synthesized as pre-pro-peptides which are secreted from cells in a primarily inactive form called latent TGF-β 18 consisting of a 25 kD mature region surrounded by the pro region, which is also called the latency associated peptide (figure 1).…”

LRP5, low-density-lipoprotein-receptor-related protein 5, is a determinant for bone mineral density

“…Analysis of a monogenic disorder, Camurati-Engelmann disease (MIM #131300), uncovered TGF-b1 as one regulatory factor of bone metabolism (Kinoshita et al 2000;Saito et al 2001). A T-to-C transition at the nucleotide position +29 in the signal sequence region of the TGF-b1 gene (TGFB1) showed a significant association with bone mass at the lumbar spine in Japanese postmenopausal women (Yamada et al 1998).…”