To understand the molecular bases for cytokine redundancy and pleiotropy, we have compared the Stat proteins activated in peripheral blood lymphocytes (PBLs) by cytokines with shared and distinct actions. Interleukin-2 (IL-2) rapidly activated Stat5 in fresh PBL, and Stat3 and Stat5 in preactivated PBL. IL-7 and IL-15 induced the same complexes as IL-2, a feature explained by the existence of similar tyrosine-phosphorylated motifs in the cytoplasmic domains of IL-2R beta and IL-7R that can serve as docking sites for Stat proteins. IL-13 Induced the same complexes as IL-4, a finding explained by our studies implicating IL-4R as a shared component of the receptors. These studies demonstrate that a single cytokine can activate different combinations of Stat proteins under different physiological conditions, and also indicate two mechanisms by which distinct cytokines can activate the same Stat protein.

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The biological activity of TGF-fl, an important modulator of cell proliferation and extracellular matrix formation, is governed by dissociation of mature TGF-t6 from an inactive, latent TGF-f complex in a process that is critical to its role in vivo. So far, it has not been possible to monitor activation in vivo since conventional immunohistochemical detection does not accurately discriminate latent versus active TGF-fl, nor have events associated with activation been defined well enough to serve as in situ markers of this process. We describe here a modified immunodetection method using differential antibody staining that allows the specific detection of active versus latent TGF-fl.Under these conditions, we report that an antibody raised to latency-associated peptide detects latent TGF-j6, and we demonstrate that LC(1-30) antibodies specifically recognize active TGF-#1 in tumor xenografts overproducing active TGF-fil, without cross-reactivity in tumors expressing similar levels of latent TGF-fl1. We previously reported that TGF-ft immunoreactivity increases in murine mammary gland after whole-body 'Co-'y radiation exposure. Using differential antibody staining we now show that radiation exposure specifically generates active TGF-f1. While latent TGF-,61 was widely distributed in unirradiated tissue, active TGF-ftl distribution was restricted.Active TGF-#1 increased significantly within 1 h of irradiation concomitant with decreased latent TGF-ft immunoreactivity.This rapid shift in immunoreactivity provides the first evidence for activation of TGF-ft in situ. This reciprocal pattern of expression persisted for 3 d and was accompanied by decreased recovery of latent TGF-#1 from irradiated tissue. Radiation-induced activation of TGF-ft may have profound implications for understanding tissue effects caused by radiation therapy. (J.

The three-dimensional structure of a member of the β subfamily of chemokines, human macrophage inflammatory protein-1β (hMIP-1β), has been determined with the use of solution multidimensional heteronuclear magnetic resonance spectroscopy. Human MIP-1β is a symmetric homodimer with a relative molecular mass of ∼16 kilodaltons. The structure of the hMIP-1β monomer is similar to that of the related α chemokine interleukin-8 (IL-8). However, the quaternary structures of the two proteins are entirely distinct, and the dimer interface is formed by a completely different set of residues. Whereas the IL-8 dimer is globular, the hMIP-1β dimer is elongated and cylindrical. This provides a rational explanation for the absence of cross-binding and reactivity between the α and β chemokine subfamilies. Calculation of the solvation free energies of dimerization suggests that the formation and stabilization of the two different types of dimers arise from the burial of hydrophobic residues.

The topological similarity of IL-10 to IFN gamma was totally unexpected, and may be a reflection of the close relationship between the biological effects of these two cytokines. The structure of IL-10 provides insights into the possible modes of conversion of the dimer into monomers, and of putative sites of receptor interactions. The good level of refinement and high resolution of this structure show that the internal disorder often associated with other helical cytokines is not an essential feature of this class of proteins.