Under normal physiological conditions, PTH-related protein (PTHrP) is produced in a wide variety of tissues and is thought to act locally in an autocrine or paracrine fashion more analogous to cytokines than to classic hormones such as PTH. In addition, we have recently shown that, like cytokines, PTHrP is induced in the spleen during the response to sublethal doses of endotoxin [lipopolysaccharide (LPS)] an effect that is mediated by tumor necrosis factor (TNF). As complex cytokine cascades are induced in response to infectious or inflammatory stimuli, the effects of other prototypical inflammatory [interferon-gamma (IFN gamma)] or antiinflammatory [interleukin-4 (IL-4)] cytokines on PTHrP gene expression were studied. Paradoxically, IFN gamma (50 micrograms), a cytokine that usually synergizes with TNF, inhibited LPS induction of splenic PTHrP messenger RNA (mRNA) levels in LPS-sensitive C3H/OuJ (OuJ) and LPS-resistant C3H/HeJ (HeJ) mice. The stimulation of splenic PTHrP mRNA levels caused by the administration of TNF alpha or interleukin-1 beta was similarly inhibited by IFN gamma, a type II interferon. In contrast, IFN alpha (50 micrograms), a type I interferon, stimulated splenic levels of PTHrP mRNA. IL-4, a prototypical antiinflammatory cytokine, also had a paradoxical effect on LPS induction of splenic PTHrP mRNA levels. Instead of inhibiting LPS induction of splenic PTHrP mRNA levels in OuJ or HeJ mice, IL-4 (200 ng) actually stimulated PTHrP mRNA levels. These complex cytokine interactions suggest that the expression of PTHrP in response to infectious or inflammatory stimuli depends on the counterbalancing effects of the specific cytokine networks induced by each stimulus.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.