The role of nitric oxide in the biological activity of prolactin in the mouse mammary gland

Activation of RAW264.7 mouse macrophage cells in vitro through treatment with recombinant ricin toxin-binding subunit B: involvement of protein tyrosine, NF-κB and JAK-STAT kinase signaling pathways

Ricin toxin-binding subunit B (RTB) is a galactose-binding lectin protein. In the present study, we investigated the effects of RTB on inducible nitric oxide (NO) synthase (iNOS), interleukin (IL)-6 and tumor necrosis factor (TNF)-α, as well as the signal transduction mechanisms involved in recombinant RTB-induced macrophage activation. RAW264.7 macrophages were treated with RTB. The results revealed that the mRNA and protein expression of iNOS was increased in the recombinant RTB-treated macrophages. TNF-α production was observed to peak at 20 h, whereas the production of IL-6 peaked at 24 h. In another set of cultures, the cells were co-incubated with RTB and the tyrosine kinase inhibitor, genistein, the phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002, the p42/44 inhibitor, PD98059, the p38 inhibitor, SB203580, the JNK inhibitor, SP600125, the protein kinase C (PKC) inhibitor, staurosporine, the JAK2 inhibitor, tyrphostin (AG490), or the NOS inhibitor, L-NMMA. The recombinant RTB-induced production of NO, TNF-α and IL-6 was inhibited in the macrophages treated with the pharmacological inhibitors genistein, LY294002, staurosporine, AG490, SB203580 and BAY 11-7082, indicating the possible involvement of protein tyrosine kinases, PI3K, PKC, JAK2, p38 mitogen-activated protein kinase (MAPK) and nuclear factor (NF)-κB in the above processes. A phosphoprotein analysis identified tyrosine phosphorylation targets that were uniquely induced by recombinant RTB and inhibited following treatment with genistein; some of these proteins are associated with the downstream cascades of activated JAK-STAT and NF-κB receptors. Our data may help to identify the most important target molecules for the development of novel drug therapies.

Growth hormone receptor deficiency in mice results in reduced systolic blood pressure and plasma renin, increased aortic eNOS expression, and altered cardiovascular structure and function

To study the role of the growth hormone receptor (GHR) in the development of cardiovascular structure and function, female GHR gene-disrupted or knockout (KO) and wild-type (WT) mice at age 18 wk were used. GHR KO mice had lower plasma renin levels (12 +/- 2 vs. 20 +/- 4 mGU/ml, P < 0.05) and increased aortic endothelial NO synthase (eNOS) expression (146%, P < 0.05) accompanied by a 25% reduction in systolic blood pressure (BP, 110 +/- 4 vs. 147 +/- 3 mmHg, P < 0.001) compared with WT mice. Aldosterone levels were unchanged, whereas the plasma potassium concentration was elevated by 14% (P < 0.05) in GHR KO. Relative left ventricular weight was 14% lower in GHR KO mice (P < 0.05), and cardiac dimensions as analyzed by echocardiography were similarly reduced. Myograph studies revealed a reduced maximum contractile response in the aorta to norepinephrine (NE) and K(+) (P < 0.05), and aorta media thickness was decreased in GHR KO (P < 0.05). However, contractile force was normal in mesenteric arteries, whereas sensitivity to NE was increased (P < 0.05). Maximal acetylcholine-mediated dilatation was similar in WT and GHR KO mice, whereas the aorta of GHR KO mice showed an increased sensitivity to acetylcholine (P < 0.05). In conclusion, loss of GHR leads to low BP and decreased levels of renin in plasma as well as increase in aortic eNOS expression. Furthermore, GHR deficiency causes functional and morphological changes in both heart and vasculature that are beyond the observed alterations in body size. These data suggest an important role for an intact GH/IGF-I axis in the maintenance of a normal cardiovascular system.

Production of nitric oxide by murine peritoneal macrophages in vitro on treatment with prolactin and growth hormone: Involvement of protein tyrosine kinases, Ca++, and MAP kinase signal transduction pathways

Prolactin (PRL) and growth hormone (GH) (somatotropin) have been known to possess immunomodulatory properties. In the present studies we have investigated the production of nitric oxide (NO) and TNF-alpha by murine peritoneal macrophages in vitro on treatment with PRL and GH and the signal transduction mechanism involved. It is observed that significantly enhanced production of NO is induced in macrophages on treatment with PRL and GH. It is further observed that protein tyrosine kinases, MAP kinases and Ca(++) channeling are involved in NO production by macrophages on in vitro treatment with PRL and GH. GH and PRL induced nitric oxide did not have any effect on the expression and production of TNF-alpha. PRL or GH induced TNF-alpha production by murine macrophages was insensitive in the presence of competitive inhibitor of NOS, L-NMMA. Similarly, there is no autocrine or paracrine effect of TNF-alpha on GH or PRL induced NO production and iNOS expression.

The compartmentalization of prolactin signaling in the mouse mammary gland

In mammary epithelial cells, prolactin (PRL) activates at least two signaling pathways: Jak/Stat and nitric oxide (NO). The former induces differentiation as measured by alpha-lactalbumin accumulation, while experiments with sodium nitroprusside (SNP) show that NO inhibits differentiation. In order to resolve this apparent contradiction, the kinetics, inducibility, and cellular localization of NO production and sensitivity in mammary cells were examined. First, mammary cells remained responsive to PRL throughout the incubation with respect to NO production. Second, although desensitization occurred with continuous PRL exposure, recovery began as quickly as 30 min after PRL withdrawal. Since PRL is secreted in pulses in vivo, complete desensitization was not a likely explanation for the cells' escape from NO inhibition. Finally, the cellular site of transduction was examined using the caveolar disrupting agent, methyl-beta-cyclodextrin (MBCD). MBCD inhibited the accumulation of PRL-induced NO but not alpha-lactalbumin. This finding was confirmed by membrane fractionation studies where the PRL-induced NO production occurred primarily in caveolae and PRL-stimulated tyrosine phosphorylation of Stat5, which transcribes the alpha-lactalbumin gene, occurred predominantly in noncaveolar membranes. Finally, endogenous elevations of NO by arginine did not inhibit differentiation. As such, the inhibition seen with SNP appeared to be an artifact of the ubiquitous generation of NO from SNP. Physiologically, PRL induces NO only in caveolae and this restricted distribution does not interfere with differentiation.

Constitutive Coexpression of Nitric Oxide Synthase-1 and Soluble Guanylyl Cyclase in Myoepithelial Cells of Mammary Glands in Mice

An impact of nitric oxide (NO) on lactation and milk secretion in mammary glands has previously been documented, but the underlying molecular mechanisms for this modulatory effect remain unclear. Therefore, we investigated the expression patterns of NO synthase (NOS)-1, NOS-3 and the NO receptor soluble guanylyl cyclase (sGC) in mammary glands of lactating and non-lactating female C57/Bl6 mice. RT-PCR demonstrated the existence of NOS-1-mRNA and NOS-3-mRNA in both lactating and resting mammary tissue. Immunoblots loaded with equal amounts of homogenate proteins from lactating and resting mammary tissues revealed comparable intensities of NOS-1 and sGC bands. Performing catalytic NADPH diaphorase histochemistry and immunohistochemistry, NOS-1 was only detected in myoepithelial cells (MEC), while sGC was localized in alveolar epithelial cells (lactocytes) and MEC in both lactating and non-lactating mammary glands. The non-modulated co-expression of both enzymes suggests that NOS-1 and sGC contribute to the constitutive regulation of tone in MEC.

Maternal behaviors: central integration or independent parallel circuits? Theoretical comment on Popeski and Woodside (2004)

N. Popeski and B. Woodside (2004) report that the injection of L-NAME into the 3rd ventricle, which would suppress the synthesis of nitric oxide, disrupts both maternal retrieval of pups and maternal aggression in postpartum rats. These findings are discussed around the question of whether a single central integrative site regulates retrieval and maternal aggression or whether independent neural mechanisms, each dependent upon nitric oxide, regulate the 2 behaviors. A case is made for each point of view. Future research utilizing direct injections of L-NAME into specific neural sites is needed to resolve this important question.

The mechanisms by which nitric oxide affects mammary epithelial growth and differentiation

Nitric oxide (NO) enhances prolactin-stimulated DNA synthesis and inhibits prolactin-induced differentiation in mouse mammary epithelium. The molecular pathways used by NO were determined by employing specific inhibitors of the transducers utilized by NO. Inhibitors of the Jun N-terminal kinase (JNK) blocked the effect of NO on DNA synthesis, although this appeared to involve a protein kinase G (PKG)-independent pathway. In contrast, inhibitors of the extracellular signal-regulated kinase (ERK) prevented NO from suppressing alpha-lactalbumin accumulation and this effect was PKG-dependent. NO can also elevate cAMP through the inhibition of phosphodiesterase 3 and cAMP mimicks the actions of NO on both DNA synthesis and differentiation. However, suppression of cAMP levels did not prevent the effects of NO. Therefore, NO uses two separate pathways to affect mammary epithelium: it stimulates growth via JNK and inhibits differentiation through ERK.