Studies on the prolactin-releasing mechanism of histones H2A and H2B

Characterization, localization and possible anti-inflammatory function of rat histone H4 mRNA variants

Two histone H4 mRNA variants, H4-v.1 and histogranin mRNAs, were detected in the rat genome and measured in various tissues and isolated alveolar macrophages. Medium to high levels of both mRNAs were present in the liver, adrenal glands, thymus, bone marrow and alveolar macrophages. H4-v.1 cDNA contained an open reading frame that coded for unmodified whole histone H4, whereas histogranin cDNA lacked the first ATG codon and contained an open reading frame that coded for modified (Thr89) H4-(84-102). The two genes displayed a sequence homologous (> 80%) to the open reading frame of core H4 somatic (H4s) and H4 germinal (H4g) and their variant nature was supported by the absence of histone consensus palindromic and purine-rich sequences in the proximal 3'UTR, and the presence of a polyadenylation signal in the distal 3'UTR and of specific upstream transcription factor-binding sites. H4-v.1 and histogranin transcripts, but not H4s transcript, were selectively induced by lipopolysaccharide and/or interferon gamma in alveolar macrophages. In vitro transcription/translation experiments with H4-v.1 and histogranin cDNA pCMV constructs produced peptides with the molecular mass (2 kDa) of the alternative histone H4 translation product which, like synthetic H4-(86-100) and [Thr89]H4-(86-100) or rat histogranin, inhibited lipopolysaccharide-induced prostaglandin E(2) release from rat alveolar macrophages. The synthetic peptides also inhibited the secretion of the CXC chemokine interleukin-8 (GRO/CINC-1) in response to lipopolysaccharide. The presence of H4-v.1 and histogranin mRNAs in tissues wherein immune reactions take place and the inhibitory effects of their translation products on prostaglandin E(2) and interkeukin-8 secretion by activated alveolar macrophages suggest an anti-inflammatory function.

Calmodulin is a critical regulator of osteoclastic differentiation, function, and survival

Increased osteoclastic resorption and subsequent bone loss are common features of many debilitating diseases including osteoporosis, bone metastases, Paget's disease, and rheumatoid arthritis. While rapid progress has been made in elucidating the signaling pathways directing osteoclast differentiation and function, a comprehensive picture is far from complete. Here, we explore the role of the Ca(2+)-activated regulator calmodulin in osteoclastic differentiation, functional bone resorption, and apoptosis. During active bone resorption, calmodulin expression is increased, and calmodulin concentrates at the ruffled border, the organelle utilized for acid transport and bone dissolution. Pharmacologic inhibitors of calmodulin, several of which are already used clinically as anti-cancer and anti-psychotic agents, inhibit osteoclastic acid transport, suggesting their potential as bone-sparing drugs. Recent studies also implicate calmodulin in osteoclast apoptosis through a mechanism involving its direct interaction with the death receptor Fas. During osteoclastogenesis, RANKL-induction stimulates a rise in intracellular Ca2+, which in turn activates calmodulin and its downstream effectors. In particular, the Ca(2+)/calmodulin-dependent phosphatase calcineurin and its targets, the NFAT family of transcription factors, have been posited as the master regulators of osteoclastogenesis. However, recent in vivo and in vitro studies demonstrate that another Ca(2+)/calmodulin-regulated effector protein, CaMKII, is also involved. CaMKII(+/-) mutant mice have reduced osteoclast numbers, and CaMKII antagonists inhibit osteoclastogenesis in vitro. Furthermore, CaMKII is known to activate AP-1 transcription factors, which are also required for RANKL-induced osteoclast gene transcription, and recent findings suggest that CaMKII can down-regulate gp130, a cytokine receptor involved in bone remodeling and implicated in numerous osteo-articular diseases.

The role of calmodulin in the regulation of osteoclastogenesis

Calmodulin plays an important role in regulating the function of mature osteoclasts. However, its role in osteoclastogenesis has not been investigated. In the present study, we examined the role of calmodulin in osteoclastogenesis using in vivo and in vitro systems. Calmodulin antagonists, trifluoperazine (TFP), W7, and tamoxifen, dose-dependently inhibited osteoclast formation, which occurred only in the last 24 h of a 4-d osteoclastogenesis culture using mouse bone marrow macrophages. Inhibitory effects were quantitated by measuring tartrate-resistant acid phosphatase activity and counting osteoclast numbers. In contrast, bis indolylmaleimide, a protein kinase C inhibitor, showed no such inhibitory effect even when applied at a concentration that was 10-fold greater than its IC50. Overexpressing calmodulin by recombinant retrovirus reversed the inhibitory effect of TFP on osteoclast-like differentiation in RAW264.7 cells. Furthermore, administration of TFP to mice was as effective as estrogen in abolishing the ovariectomy-induced increment of osteoclastogenesis as determined by quantitative assessment of tartrate-resistant acid phosphatase activity in tibias, which led to the recovery of the ovariectomy-induced decrement in trabecular bone volume. To investigate potential cellular and molecular mechanisms by which calmodulin antagonists inhibit osteoclastogenesis, Z-VAD-FMK, a broad caspase inhibitor, failed to block the inhibitory effect of TFP on mouse osteoclast formation, indicating that apoptosis is not the underlying mechanism. Pretreatment of RAW264.7 cells with different concentrations of TFP dose-dependently inhibited receptor activator of nuclear factor kappaB ligand-stimulated phosphorylation of c-Jun N-terminal kinase and inhibitory kappaBalpha but not that of p38. Taken together, our data indicate that calmodulin mediates osteoclast differentiation, possibly via modulating specific receptor activator of NF-kappaB-signaling pathways.

Hypophysiotropic activity of histone H3 in vitro

To assess the effect of histone H3 on pituitary hormone secretion, rat anterior pituitary (AP) cells were used and growth hormone, prolactin, thyrotropin, luteinizing hormone and follicle stimulating hormone measured by radioimmunoassay. Incubation of cells with H3 (1, 6, and 30 microM) stimulated the release of all five hormones in a dose-dependent manner. This effect was blocked by preincubation of H3 with an anti-H3 antibody. Incubation of AP cells with 6 microM H3 in the presence of specific AP hormone secretagogues (GRP-6, thyrotropin-releasing hormone (TRH), gonadotropin-releasing hormone (GnRH)) showed additive effects on hormone secretion. Pharmacological experiments suggested that calcium- and diacylglycerol- (DAG) associated pathways, but not cAMP, participate in the hypophysiotropic activity of H3. Our results confirm previous evidence that histones may act as hypophysiotropic signals.