Both structural and inflammatory cells are capable of secreting transforming growth factor (TGF)-b and expressing TGF-b receptors. TGF-b can induce multiple cellular responses including differentiation, apoptosis, survival and proliferation, and has been implicated in the development of several pathogenic conditions including cancer and asthma. Elevated levels of TGF-b have been reported in the asthmatic airway. TGF-b binds to its receptor complex and activates multiple pathways involving proteins such as Sma and Mad homologues, phosphatidylinositol-3 kinase and the mitogen-activated protein kinases, leading to the transcription of several genes. Cell type, cellular condition, and microenvironment, all play a role in determining which pathway is activated, which, in turn, is an indication of which gene is to be transcribed. TGF-b has been shown to induce apoptosis in airway epithelial cells. A possible role for TGF-b in the regulation of epithelial cell adhesion properties has also been reported. Enhancement of goblet cell proliferation by TGF-b suggests a role in mucus hyper-secretion. Elevated levels of TGF-b correlate with subepithelial fibrosis. TGF-b induces proliferation of fibroblast cells and their differentiation into myofibroblasts and extracellular matrix (ECM) protein synthesis during the development of subepithelial fibrosis. TGF-b also induces proliferation and survival of and ECM secretion in airway smooth muscle cells (ASMCs), suggesting a possible cause of increased thickness of airway tissues. TGF-b also induces the production and release of vascular endothelial cell growth factor and plasminogen activator inhibitor, contributing to the vascular remodeling in the asthmatic airway. Blocking TGF-b activity inhibits epithelial shedding, mucus hyper-secretion, angiogenesis, ASMC hypertrophy and hyperplasia in an asthmatic mouse model. Reduction of TGF-b production and control of TGF-b effects would be beneficial in the development of therapeutic intervention for airway remodeling in chronic asthma.

DNA methylation is one of several epigenetic changes observed in cells. Aberrant methylation of tumor suppressor genes, proto-oncogenes, and vital cell cycle genes has led many scientists to investigate the underlying cellular mechanisms of DNA methylation under normal and pathological conditions. Although DNA methylation is necessary for normal mammalian embryogenesis, both hypo-and hypermethylation of DNA are frequently observed in carcinogenesis and other pathological disorders. DNA hypermethylation silences the transcription of many tumor suppressor genes, resulting in immortalization of tumor cells. The reverse process, demethylation and restoration of normal functional expression of genes, is augmented by DNA methylation inhibitors. Recent studies suggest that DNA hypomethylation may also control gene expression and chromosomal stability. However, the roles of and relationship between hypomethylation and hypermethylation are not well understood. This review provides a brief overview of the mechanism of DNA methylation, its relationship to extrinsic stimulation including dietary intake and aging, and of abnormally methylated DNA in breast and colorectal cancers, which could be used as prognostic and diagnostic markers.

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The temperature-dependent dissociation of /?-casein from the casein micelles of milk and from the soluble casein complexes of colloidal phosphate-free (CPF) milk was investigated by high-speed centrifugation and gel-filtration. The percentage of the total casein in supernatants prepared by high-speed centrifugation of mid-lactation milks increased from approximately 6 to 15% on cooling the milks from 30 to 5 °C; y?-casein accounted for about 46 % of this increase, while a 8 -and /c-casein constituted 30 and 23%, respectively. On gel-filtration both of skimmilk and CPF milk on Sepharose 2B at 0, 2, 5, 10 and 25 C C, maximum amounts of free /?-casein (c. 60 % of total) were obtained at 5 °C. The remainder of the yff-casein appeared to be more strongly bound to the a s -and /c-casein and may be involved in the internal cohesion of casein micelles. The free /?-casein of both milk preparations appeared to be in equilibrium with the bound /?-casein. On Sephadex G-200 columns at 5 °C, approximately 5 and 60 % of the yS-casein of skim-milk and CPF milk, respectively, was eluted in the free form in the expected position for a globular protein of molecular weight about 200000. At low temperatures, particularly at 5 °C, colloidal phosphate appeared to play an integrating role in the association of over half the total y?-casein with the other casein components of native micelles. However, when the equilibrium between micellar and free /?-casein was disturbed by gel-filtration on Sepharose 2B, the presence of colloidal phosphate did not prevent the release of most of the /?-casein from casein micelles. Some problems encountered in the use of densitometry for the estimation of individual caseins on electropherograms are described.It has been suggested (Sullivan et al. 1955) that /?-casein is removed from casein micelles when skim-milk is chilled. More recently Rose (1968) demonstrated that /?-casein constituted about 55 % of the total increase in serum casein obtained by storing milk overnight at 4 °C.In the present investigation the relative amounts of free and bound /?-casein present in milk and in CPF milk at various temperatures between 0 and 30 °C were determined by high-speed centrifugation and gel-filtration. The hypothesis (cf. Rose, 1969) that /?-casein constitutes the internal lattice or framework of casein micelles was further investigated by studying the effect of 23-2

Weakly polar interactions between aromatic rings of amino acids and hydrogens of backbone amides (Ar-HN) have been shown to support local structures in proteins. Their role in secondary structures, however, has not been elucidated. To investigate the relationship between Ar-HN interaction and the stability of local and secondary structures of polypeptides and to improve the prediction of this interaction based on amino acid sequence, the structures of 560 nonhomologous proteins, from the Protein Data Bank, were searched for Ar-HN interactions between the aromatic ring of each Phe, Tyr, and Trp residue at position i and the backbone amide group of any residue, except Pro, at the positions i, i - 1, i - 2, i - 3, i + 1, i + 2, and i + 3. Ar-HN interactions were identified by calculating the chemical shift of the amide hydrogen caused by the proximal aromatic ring. Ar(i)-HN(i + 1, i + 2 and i + 3) interactions were more common (7.10%, 2.08%, and 0.54%, respectively) than were Ar(i)-HN(i - 1, i - 2, and i - 3) interactions (0.66%, <0.1%, and 0.18%, respectively). The value of the chi(1) torsion angle of the aromatic residue in position i depended on the direction of the Ar-HN interaction. The position of the aromatic ring in Ar(i)-HN(i + 1, i + 2, and i + 3) interactions was mostly trans, in Ar(i)-HN(i - 1, i - 2, and i - 3) interactions mainly gauche(-), and in Ar(i)-HN(i) interactions mostly gauche(+). The analyses of the secondary structures of the protein fragments containing Ar-HN interactions showed that Ar-HN interactions were in all types of secondary structures. Search results suggest that Ar-HN interactions have a stabilizing effect on all types of secondary structures.