Human recombinant interferon-inducible protein-10: intact disulfide bridges are not required for inhibition of hematopoietic progenitors and chemotaxis of T lymphocytes and monocytes

The Solution Structure of CCL28 Reveals Structural Lability that Does Not Constrain Antifungal Activity

The chemokine CCL28 is constitutively expressed in mucosal tissues and is abundant in low-salt mucosal secretions. Beyond its traditional role as a chemoattractant, CCL28 has been shown to act as a potent and broad-spectrum antimicrobial agent with particular efficacy against the commensal fungus and opportunistic pathogen Candida albicans. However, the structural features that allow CCL28 to perform its chemotactic and antimicrobial functions remain unknown. Here, we report the structure of CCL28, solved using nuclear magnetic resonance spectroscopy. CCL28 adopts the canonical chemokine tertiary fold, but also has a disordered C-terminal domain that is partially tethered to the core by a non-conserved disulfide bond. Structure-function analysis reveals that removal of the C-terminal tail reduces the antifungal activity of CCL28 without disrupting its structural integrity. Conversely, removal of the non-conserved disulfide bond destabilizes the tertiary fold of CCL28 without altering its antifungal effects. Moreover, we report that CCL28 unfolds in response to low pH but is stabilized by the presence of salt. To explore the physiologic relevance of the observed structural lability of CCL28, we investigated the effects of pH and salt on the antifungal activity of CCL28 in vitro. We found that low pH enhances the antifungal potency of CCL28, but also that this pH effect is independent of CCL28's tertiary fold. Given its dual role as a chemoattractant and antimicrobial agent, our results suggest that changes in the salt concentration or pH at mucosal sites may fine-tune CCL28's functional repertoire by adjusting the thermostability of its structure.

Coupling of contact sensitizers to thiol groups is a key event for the activation of monocytes and monocyte-derived dendritic cells

Strong contact sensitizers are able to induce distinct signal transduction mechanisms in antigen-presenting cells by coupling to cell proteins. The predominant target structures of haptens are thought to be thiol and amino groups in cysteine and lysine residues. We studied whether coupling of small reactive chemicals to thiol or amino groups might be responsible for the activation of monocytes and mature monocyte-derived dendritic cells. Human peripheral blood mononuclear cells were stimulated in vitro with subtoxic concentrations of the strong haptens 5-chloro-2-methylisothiazolinone plus 2-methylisothiazolinone and 2, 4, 6-trinitrochlorobenzene, the thiol-reactive reagents N-hydroxymaleimide and N-ethylmaleimide, as well as the amino-reactive compounds sulfosuccinimidyl acetate and 2-iminothiolane. Flow cytometric quantification of tyrosine phosphorylation in CD14+ monocytes showed that 5-chloro-2-methylisothiazolinone plus 2-methylisothiazolinone, 2, 4, 6-trinitrochlorobenzene, N-hydroxymaleimide, and N-ethylmaleimide but not sulfosuccinimidyl acetate and 2-iminothiolane strongly induced this process. Tyrosine phosphorylation induced by 5-chloro-2-methylisothiazolinone plus 2-methylisothiazolinone and 2, 4, 6-trinitrochlorobenzene was completely prevented in the presence of cysteine but not lysine, suggesting a competitive mechanism between cysteine and sulfhydryl groups of cell proteins. Using the mouse ear swelling test N-hydroxymaleimide could be classified as a significant contact allergen in comparison to 2, 4, 6-trinitrochlorobenzene, whereas no sensitizing potential became apparent for sulfosuccinimidyl acetate and 2-iminothiolane. Western blot analysis on monocytes and mature monocyte-derived dendritic cells confirmed the flow cytometric data for tyrosine phosphorylation and demonstrated a selective capacity of haptens and thiol-reactive compounds to activate ERK1/2 mitogen-activated protein kinase. Our data show that strong affinity of a small reactive chemical toward thiol groups is important for the activation of monocytes and monocyte-derived dendritic cells and can support the process of sensitization.

Structure, function, and inhibition of chemokines

Chemokines are the largest family of cytokines in human immunophysiology. These proteins are defined by four invariant cysteines and are categorized based on the sequence around the first two cysteines, which leads to two major and two minor subfamilies. Chemokines function by activating specific G protein-coupled receptors, which results in, among other functions, the migration of inflammatory and noninflammatory cells to the appropriate tissues or compartments within tissues. Some of these proteins and receptors have been implicated or shown to be involved in inflammation, autoimmune diseases, and infection by HIV-1. The three-dimensional structure of each monomer is virtually identical, but the quaternary structure of chemokines is different for each subfamily. Structure-function studies reveal several regions of chemokines to be involved in function, with the N-terminal region playing a dominant role. A number of proteins and small-molecule antagonists have been identified that inhibit chemokine activities. In this review, we discuss aspects of the structure, function, and inhibition of chemokines.

Regulation of hematopoiesis by chemokine family members

Chemokines, originally designated as chemoattractant cytokines, comprise a large family of molecules that have been implicated in a number of different functions mediated through chemokine receptors. Among these functions are regulatory roles in hematopoiesis that encompass effects on the proliferation, survival, and homing/migration of myeloid progenitor cells. This article reviews the field of chemokine regulation of hematopoiesis at the level of myeloid progenitor cells.