Distribution and functional characterization of pituitary adenylate cyclase-activating polypeptide receptors in the brain of non-human primates

The distribution and density of pituitary adenylate cyclase-activating polypeptide (PACAP) binding sites have been investigated in the brain of the primates Jacchus callithrix (marmoset) and Macaca fascicularis (macaque) using [(125)I]-PACAP27 as a radioligand. PACAP binding sites were widely expressed in the brain of these two species with particularly high densities in the septum, hypothalamus and habenula. A moderate density of recognition sites was seen in all subdivisions of the cerebral cortex with a heterogenous distribution, the highest concentrations occurring in layers I and VI while the underlying white matter was almost devoid of binding sites. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed intense expression of the mRNAs encoding the short and hop-1 variants of pituitary adenylate cyclase-activating polypeptide-specific receptor (PAC1-R) in the cortex of both marmoset and macaque, whereas vasoactive intestinal polypeptide/pituitary adenylate cyclase-activating polypeptide mutual receptor, subtype 1 (VPAC1-R) and vasoactive intestinal polypeptide/pituitary adenylate cyclase-activating polypeptide mutual receptor, subtype 2 (VPAC2-R) mRNAs were expressed at a much lower level. In situ hybridization histochemistry showed intense expression of PAC1-R and weak expression of VPAC1-R mRNAs in layer IV of the cerebral cortex. Incubation of cortical tissue slices with PACAP induced a dose-dependent stimulation of cyclic AMP formation, indicating that PACAP binding sites correspond to functional receptors. Moreover, treatment of primate cortical slices with 100 nM PACAP significantly reduced the activity of caspase-3, a key enzyme of the apoptotic cascade. The present results indicate that PACAP should exert the same neuroprotective effect in the brain of primates as in rodents and suggest that PAC1-R agonists may have a therapeutic value to prevent neuronal cell death after stroke or in specific neurodegenerative diseases.

Gene expression profiles in psoriasis: analysis of impact of body site location and clinical severity

BACKGROUND

Psoriasis is characterized by symmetry of plaques and modulation of multiple genes within those plaques.

OBJECTIVES

We compared gene expression profiles of plaques of psoriasis at different anatomical sites for both symmetrical and asymmetrical disease to ascertain whether the same genes were expressed.

METHODS

Gene expression profiles were analysed in biopsies from lesional and uninvolved skin from two groups of patients with either predominantly symmetrical or truncal plaques of psoriasis vulgaris, and from normal skin of healthy volunteers. Genomic analyses were performed using cDNA array and kinetically monitored reverse transcriptase-initiated polymerase chain reaction (kRT-PCR) approaches. A cluster of genes upregulated in involved psoriasis skin as compared with normal skin was identified using each of these two technologies.

RESULTS

Clustering of patients based on their gene expression profile did not reveal any correlation with family history of psoriasis, age at onset or association of psoriasis with arthritis. There was no difference in gene expression profile between the type (symmetrical vs. truncal) or location (left vs. right side of body) of psoriatic plaques. Gene expression profiles of involved psoriatic skin analysed by kRT-PCR analysis did correlate with both global (Psoriasis Area and Severity Index) and local (erythema, desquamation and plaque elevation) clinical severity.

CONCLUSIONS

These results indicate that it may be feasible to analyse the molecular effects of pharmacological agents on psoriatic skin in 'minizone' protocols, that the obtained data can be correlated with clinical severity and that plaques of psoriasis in the same individual express the same genes.

Effects of retinoic acid receptor-selective agonists on human nasal epithelial cell differentiation

Retinoids play a critical role in the maintenance of the mucociliary phenotype of epithelial cells in the upper respiratory tract. To determine the role of retinoic acid receptors (RARs) in the regulation of epithelial differentiation, we tested the effect of the synthetic retinoids CD336, CD2019, and CD666, selective agonists for RARalpha, RARbeta, and RARgamma, respectively, during differentiation of human nasal epithelial (HNE) cells in vitro. Using glutamylated tubulin and transglutaminase I (Tg I) as markers of ciliated cell and squamous cell differentiation, respectively, we showed that retinoic acid (RA) stimulated mucociliary differentiation and, in parallel, inhibited squamous cell differentiation. The agonists of the three RARs independently induced ciliogenesis and inhibited squamous cell differentiation by downregulating Tg I expression in a dose- and time-dependent manner. Antagonists specific for the three RARs abolished the effects of the corresponding agonists, demonstrating an RAR-specific mediated effect. Moreover, treatment of retinoid-deficient cultures with RAR agonists induced conversion of the squamous-like phenotype into a ciliated phenotype. In conclusion, all three RARs are potentially involved in the differentiating effects of RA in respiratory epithelial cells.

Cell death in HIV pathogenesis and its modulation by retinoids

Patients infected with the human immunodeficiency virus exhibit a progressive decline in the CD4 T-cell number, resulting in immunodeficiency and increased susceptibility to opportunistic infections and malignancies. Although CD4 T cell production is impaired in patients infected with HIV, there is now increasing evidence that the primary basis of T cell depletion is accelerated apoptosis of CD4 and CD8 T cells. The rate of lymphocyte apoptosis in HIV infection correlates inversely with the progression of the disease: it is low in long-term progressors and in patients undergoing highly active antiretroviral therapy. Interestingly, only a minor fraction of apoptotic lymphocytes are infected by HIV, indicating that the enhanced apoptosis does not necessarily always serve to remove the HIV+ cells and results from mechanisms other than direct infection. Thus, understanding and influencing the mechanisms of HIV-associated lymphocyte apoptosis may lead to new therapies for HIV disease. In this paper the potential effects of retinoids on CD4 T cell apoptosis is discussed.

Activation-induced apoptosis and cell surface expression of Fas (CD95) ligand are reciprocally regulated by retinoic acid receptor alpha and gamma and involve nur77 in T cells

It has been previously shown that CD4+ T cells enter the apoptotic suicide program via the Fas ligand (FasL)/Fas-mediated pathway upon T cell receptor (TCR) stimulation. In Jurkat cells TCR stimulation regulates the de novo synthesis of FasL, while in the influenza hemagglutinin-specific CD4+ murine T cell hybridoma (IP-12-7) the cell surface appearance of a preformed FasL is initiated. Both processes are dependent on new mRNA and protein synthesis, involve up-regulation of nur77, and can be inhibited by retinoic acids (RA). Two groups of nuclear receptors for RA have been identified: retinoic acid receptors (RAR) and retinoid X receptors (RXR). In this study various synthetic retinoids were used to define which receptors regulate TCR-mediated apoptosis. It is demonstrated that the inhibition is mediated via RARalpha, while RARgamma enhances TCR-mediated apoptosis, and when both receptors are stimulated, the costimulation by RXR will promote the effect of RARalpha. Evidence is presented that these receptors affect the transcriptional activity of nur77 and consequently the expression of FasL. Our data suggest a complex interaction between the various isoforms of retinoid receptors in regulating T cell death and demonstrate that the target through which retinoids regulate TCR-mediated apoptosis is nur77.

Activation-induced apoptosis and cell surface expression of Fas (CD95) ligand are reciprocally regulated by retinoic acid receptor alpha and gamma and involve nur77 in T cells

It has been previously shown that CD4+ T cells enter the apoptotic suicide program via the Fas ligand (FasL)/Fas-mediated pathway upon T cell receptor (TCR) stimulation. In Jurkat cells TCR stimulation regulates the de novo synthesis of FasL, while in the influenza hemagglutinin-specific CD4+ murine T cell hybridoma (IP-12-7) the cell surface appearance of a preformed FasL is initiated. Both processes are dependent on new mRNA and protein synthesis, involve up-regulation of nur77, and can be inhibited by retinoic acids (RA). Two groups of nuclear receptors for RA have been identified: retinoic acid receptors (RAR) and retinoid X receptors (RXR). In this study various synthetic retinoids were used to define which receptors regulate TCR-mediated apoptosis. It is demonstrated that the inhibition is mediated via RARalpha, while RARgamma enhances TCR-mediated apoptosis, and when both receptors are stimulated, the costimulation by RXR will promote the effect of RARalpha. Evidence is presented that these receptors affect the transcriptional activity of nur77 and consequently the expression of FasL. Our data suggest a complex interaction between the various isoforms of retinoid receptors in regulating T cell death and demonstrate that the target through which retinoids regulate TCR-mediated apoptosis is nur77.

Activation-induced apoptosis and cell surface expression of Fas (CD95) ligand are reciprocally regulated by retinoic acid receptor alpha and gamma and involve nur77 in T cells

It has been previously shown that CD4+ T cells enter the apoptotic suicide program via the Fas ligand (FasL)/Fas-mediated pathway upon T cell receptor (TCR) stimulation. In Jurkat cells TCR stimulation regulates the de novo synthesis of FasL, while in the influenza hemagglutinin-specific CD4+ murine T cell hybridoma (IP-12-7) the cell surface appearance of a preformed FasL is initiated. Both processes are dependent on new mRNA and protein synthesis, involve up-regulation of nur77, and can be inhibited by retinoic acids (RA). Two groups of nuclear receptors for RA have been identified: retinoic acid receptors (RAR) and retinoid X receptors (RXR). In this study various synthetic retinoids were used to define which receptors regulate TCR-mediated apoptosis. It is demonstrated that the inhibition is mediated via RARalpha, while RARgamma enhances TCR-mediated apoptosis, and when both receptors are stimulated, the costimulation by RXR will promote the effect of RARalpha. Evidence is presented that these receptors affect the transcriptional activity of nur77 and consequently the expression of FasL. Our data suggest a complex interaction between the various isoforms of retinoid receptors in regulating T cell death and demonstrate that the target through which retinoids regulate TCR-mediated apoptosis is nur77.

Adapalene 0.1% gel and adapalene 0.1% cream stimulate retinoic acid receptor mediated gene transcription without significant irritative effects in the skin of healthy human volunteers

A randomized, investigator masked, intra individual comparative study was conducted in 30 healthy volunteers to compare the cutaneous effects of adapalene 0.1% gel and adapalene 0.1% cream with their respective vehicles, using tretinoin 0.05% cream (n = 21) or tretinoin 0.1% cream (n = 9) and a tretinoin cream vehicle (n = 30) as controls. The products were applied to hip/buttock skin for 4 days under occlusive conditions. Cytosolic retinoic acid binding protein-II (CRABP-II) mRNA levels were measured using the RT-PCR technique in punch biopsies taken from 10 subjects. Epidermal thickness was assessed using image analysis of haematoxylin and eosin stained sections from another 11 subjects. Erythema was assessed in all subjects both by a visual scoring system and by chromameter. Adapalene 0.1% gel and adapalene 0.1% cream produced similar significant increases in CRABP-II mRNA levels compared to their vehicles (P < 0.01). The two tretinoin formulations also resulted in similar significant increases in CRABP-II compared to the cream vehicle (P < 0.001). However, only the two tretinoin formulations resulted in an increase in epidermal thickness and only the tretinoin 0.1% cream resulted in significant erythema. Adapalene 0.1% gel and adapalene 0.1% cream induce RAR-mediated gene expression to a similar degree in this model, without the irritant effects of tretinoin.

Induction of apoptosis by retinoids and retinoic acid receptor gamma-selective compounds in mouse thymocytes through a novel apoptosis pathway

Retinoic acids are morphogenic signaling molecules that are derived from vitamin A and involved in a variety of tissue functions. Two groups of their nuclear receptors have been identified: retinoic acid receptors (RARs) and retinoic acid X receptors (RXRs). All-trans retinoic acid is the high affinity ligand for RARs, and 9-cis retinoic acid also binds to RXRs with high affinity. In cells at high concentrations, all-trans retinoic acid can be converted to 9-cis retinoic acid via unknown mechanisms. It was previously shown that retinoic acids prevents activation-induced death of thymocytes. Here, we report that both all-trans and 9-cis retinoic acid induce apoptosis of mouse thymocytes and purified CD4+CD8+ cells in ex vivo cultures, with 9-cis retinoic acid being 50 times more effective. The induction of apoptosis by retinoic acids is mediated by RARgamma because (a) the phenomenon can be reproduced only by RARgamma-selective retinoic acid analogs, (b) the cell death induced by either retinoic acids or RARgamma analogs can be inhibited by RARgamma-specific antagonists, and (c) CD4+CD8+ thymocytes express RARgamma. In vivo administration of an RARgamma analog resulted in thymus involution with the concomitant activation of the apoptosis-related endonuclease and induction of tissue transglutaminase. The RARgamma pathway of apoptosis is RNA and protein synthesis dependent, affects the CD4+CD8+ double positive thymocytes, and can be inhibited by the addition of either Ca2+ chelators or protease inhibitors. Using various RAR- and RXR-specific analogs and antagonists, it was demonstrated that stimulation of RAR alpha inhibits the RARgamma-specific death pathway (which explains the lack of apoptosis stimulatory effects of all-trans retinoic acid at physiological concentrations) and that costimulation of the RXR receptors (in the case of 9-cis retinoic acid) can neutralize this inhibitory effect. It is suggested that formation of 9-cis retinoic acid may be a critical element in regulating both the positive selection and the "default cell death pathway" of thymocytes.

Multifunctional activity of the extracellular domain of the M-type (180 kDa) membrane receptor for secretory phospholipases A2

M-type (180 kDa) receptors for secretory phospholipases A2 (sPLA2s) are thought to mediate some of the physiological effects of group I sPLA2, including smooth muscle contraction and cell proliferation. The M-type sPLA2 receptor is a large glycoprotein composed of several distinct extracellular domains which belongs to the C-type lectin superfamily. This receptor binds with high affinity both pancreatic group I and inflammatory group II sPLA2s as well as various sPLA2s purified from snake venoms. This paper shows that the rabbit M-type sPLA2 receptor is a multifunctional protein which is able to promote cell adhesion on type I and IV collagens most probably via its N-terminal fibronectin-like type II domain. It also shows that binding of sPLA2s to a recombinant soluble form of this receptor is associated with a noncompetitive inhibition of phospholipase A2 activity.

The human 180-kDa receptor for secretory phospholipases A2. Molecular cloning, identification of a secreted soluble form, expression, and chromosomal localization

Secretory phospholipases A2 (sPLA2) are structurally related enzymes found in mammals as well as in insect and snake venoms. They have been associated with several physiological, pathological, and toxic processes. Some of these effects are apparently linked to the existence of specific receptors for both venom and mammalian sPLA2s. We report here the molecular cloning and expression of one of these sPLA2 receptors from human kidney. Two transcripts were detected. One encodes for a transmembrane form of the sPLA2 receptor and the other one is an alternatively processed transcript, caused by polyadenylation occurring at a site within an intron in the C terminus part of the transcriptional unit. This transcript encodes for a shortened secreted soluble sPLA2 receptor lacking the coding region for the transmembrane segment. Quantitative polymerase chain reaction experiments indicate a 1.6:1 ratio between the levels of transcripts encoding for the membrane-bound and soluble forms of the receptor, respectively. Soluble and membrane-bound human sPLA2 receptors both bind sPLA2 with high affinities. However, the binding properties of the human receptors are different from those obtained with the rabbit membrane-bound sPLA2 receptor. The 180-kDa human sPLA2 receptor gene has been mapped in the q23-q24 bands of chromosome 2.

Structural elements of secretory phospholipases A2 involved in the binding to M-type receptors

Specific membrane receptors for secretory phospholipases A2 (sPLA2s) have been initially identified with novel snake venom sPLA2s called OS1 and OS2. One of these sPLA2 receptors (muscle (M)-type, 180 kDa) has a very high affinity for OS1 and OS2 and a high affinity for pancreatic and inflammatory-type mammalian sPLA2s, which might be the natural endogenous ligands of PLA2 receptors. Primary structures of OS1 and OS2 were determined and compared with sequences of other sPLA2s that bind less tightly or do not bind to the M-type receptor. In addition, the binding properties of pancreatic sPLA2 mutants to the M-type receptor have been analyzed. Residues within or close to the Ca(2+)-binding loop of pancreatic sPLA2 are crucially involved in the binding step, although the presence of Ca2+ that is essential for the enzymatic activity is not required for binding to the receptor. These residues include Gly-30 and Asp-49, which are conserved in all sPLA2s. Leu-31 is also essential for binding of pancreatic sPLA2 to its receptor. Many other mutations have been considered. Those occurring in the N-terminal alpha helices and the pancreatic loop do not change binding to the M-type receptor. Conversion of pancreatic prophospholipase to phospholipase is essential for the acquisition of binding properties to the M-type receptor.

Cloning and expression of a membrane receptor for secretory phospholipases A2

Snake venom and mammalian secretory phospholipases A2 are structurally related enzymes that have been associated with several toxic (neurotoxicity, myotoxicity, etc.), pathological (inflammation, hypersensitivity, etc.), or physiological (contraction, proliferation, etc.) processes. We have previously shown that snake venom PLA2s have specific high affinity receptors. Here, we report the molecular cloning of one of these PLA2 receptors (molecular mass approximately 180 kDa), previously purified from rabbit skeletal muscle. It is a membrane protein with a N-terminal cysteine-rich domain, a fibronectin type II domain, eight repeats of a carbohydrate recognition domain, a unique transmembrane domain, and a intracellular C-terminal domain. The 1458-residue PLA2 receptor, expressed in transfected cells, binds svPLA2 with very high affinities (Kd values approximately 10-20 pM). It also tightly binds the two structural types of msPLA2s, i.e. pancreatic PLA2 and synovial PLA2 (Kd approximately 1-10 nM). This receptor might have a key role in normal and pathological actions of secretory PLA2s.