Lipopolysaccharide induces the expression of an autocrine prolactin loop enhancing inflammatory response in monocytes

Abstract

BackgroundProlactin from pituitary gland helps maintain homeostasis but it is also released in immune cells where its function is not completely understood. Pleiotropic functions of prolactin (PRL) might be mediated by different isoforms of its receptor (PRLr).MethodsThe aim of this study was to investigate the relationship between the eventual synthesis of PRL and PRLr isoforms with the inflammatory response in monocytes. We used THP-1 and monocytes isolated from healthy subjects stimulated with lipopolysaccharide (LPS). Western blot, real time PCR and immunocytochemistry were performed to identify both molecules. The bioactivity of the PRL was assessed using a bioassay and ELISA to detect pro inflammatory cytokines.ResultsPRLr mRNA and PRL mRNA were synthesized in THP-1 monocytes activated with LPS with peaks of 300-fold and 130-fold, respectively. The long (100 kDa) and the intermediate (50 kDa) isoforms of PRLr and big PRL (60 kDa) were time-dependent upregulated for monocytes stimulated with LPS. This expression was confirmed in monocytes from healthy subjects. The PRLr intermediate isoform and the big PRL were found soluble in the culture media and later in the nucleus in THP-1 monocytes stimulated with LPS. Big PRL released by monocytes showed bioactivity in Nb2 Cells, and both PRL and PRLr, synthesized by monocytes were related with levels of nitrites and proinflammatory citokines.ConclusionsOur results suggest the expression of a full-autocrine loop of PRL enhances the inflammatory response in activated monocytes. This response mediated by big PRL may contribute to the eradication of potential pathogens during innate immune response in monocytes but may also contribute to inflammatory disorders.

A 60 kDa prolactin variant secreted by cervical cancer cells modulates apoptosis and cytokine production

“…The concentration of hormones and time of stimulus had been standardized in previous studies published by our group (24).…”

“…This PRL variant has been previously identified in peripheral blood mononuclear cells (PBMC) from patients with SLE and THP-1 monocytes (24,25).…”

“…In a previous study we provided evidence that the cell lines and tissues of cervical cancer synthesize a 60 kDa PRL variant unlike the non-tumorigenic keratinocytes (HaCaT) (23,24). This PRL variant has been previously identified in peripheral blood mononuclear cells (PBMC) from patients with SLE and THP-1 monocytes (24,25).…”

Prolactin and Prolactin Receptor Expression in Cervical Intraepithelial Neoplasia and Cancer

“…This large isoform of PRL has been previously characterized in serum, plasma, PBMC, lymphocytes and monocytes from human subjects [18][19][20]. The large PRL is a dimer of covalently-linked glycosylated subunits (25 kDa) [19] and has been formerly correlated with the course of several inflammatory disorders [21,22]. Different investigations in breast and prostate cancer suggest that autocrine prolactin may play an important role in the development of cancer [23,24].…”

The prolactin receptor is expressed in rheumatoid arthritis and psoriatic arthritis synovial tissue and contributes to macrophage activation

“…This may suggest that systemic levels of PRL (originating from the pituitary) may have a minor role in the pathology of RA, while an autocrine/paracrine loop of PRL acting in the ST may be more important. Of note, an autocrine loop of PRL could enhance the inflammatory response of activated monocytes at the site of inflammation [47]. …”