Parathyroid hormone stimulates protein kinase C but not adenylate cyclase in mouse epidermal keratinocytes

Effects of recombinant human parathyroid hormone (1-34)on cell proliferation, chemokine expression and the Hedgehog pathway in keratinocytes

Psoriasis is an autoimmune disease involving the excessive proliferation of keratinocytes mediated by T‑cells. Parathyroid hormone (PTH) has been identified as an essential factor in the treatment of psoriasis. In the present study, the mechanism underlying the effect of recombinant human parathyroid hormone (rhPTH) (1‑34) in keratinocytes was investigated. The effects of rhPTH (1‑34) on cell proliferation, cell cycle, and the secretion and expression of C‑X‑C motif chemokine 11 (CXCL11) and components of the Hedgehog signaling pathway were examined in HaCaT cells by MTT assay, flow cytometric analysis, ELISA and gene chip analysis. The data showed that rhPTH (1‑34) significantly inhibited keratinocyte proliferation at concentrations >8x10‑7 mol/l. rhPTH (1‑34) induced G1 phase arrest of the cell cycle in the keratinocytes. The secretion of CXCL11 in tumor necrosis factor (TNF)‑α‑induced keratinocytes was downregulated by rhPTH (1‑34) in a dose‑dependent manner, compared with that in keratinocytes treated with TNF‑α alone. It was also found that rhPTH (1‑34) inhibited the expression of CXCL11 in the HaCaT cells. rhPTH (1‑34) also affected the Hedgehog signaling pathway specifically by regulating the expression of associated genes. In conclusion, these data suggested that rhPTH (1‑34) inhibited cell proliferation, and the secretion and expression of CXCL11 in HaCaTs. rhPTH (1‑34) also altered the expression of associated genes in the Hedgehog pathway. Therefore, rhPTH (1‑34) can be considered as a novel therapeutic agent for the treatment of psoriasis.

PTH and Vitamin D

PTH and Vitamin D are two major regulators of mineral metabolism. They play critical roles in the maintenance of calcium and phosphate homeostasis as well as the development and maintenance of bone health. PTH and Vitamin D form a tightly controlled feedback cycle, PTH being a major stimulator of vitamin D synthesis in the kidney while vitamin D exerts negative feedback on PTH secretion. The major function of PTH and major physiologic regulator is circulating ionized calcium. The effects of PTH on gut, kidney, and bone serve to maintain serum calcium within a tight range. PTH has a reciprocal effect on phosphate metabolism. In contrast, vitamin D has a stimulatory effect on both calcium and phosphate homeostasis, playing a key role in providing adequate mineral for normal bone formation. Both hormones act in concert with the more recently discovered FGF23 and klotho, hormones involved predominantly in phosphate metabolism, which also participate in this closely knit feedback circuit. Of great interest are recent studies demonstrating effects of both PTH and vitamin D on the cardiovascular system. Hyperparathyroidism and vitamin D deficiency have been implicated in a variety of cardiovascular disorders including hypertension, atherosclerosis, vascular calcification, and kidney failure. Both hormones have direct effects on the endothelium, heart, and other vascular structures. How these effects of PTH and vitamin D interface with the regulation of bone formation are the subject of intense investigation.

Role of PDZ proteins in regulating trafficking, signaling, and function of GPCRs: means, motif, and opportunity

PDZ proteins, named for the common structural domain shared by the postsynaptic density protein (PSD95), Drosophila disc large tumor suppressor (DlgA), and zonula occludens-1 protein (ZO-1), constitute a family of 200-300 recognized members. These cytoplasmic adapter proteins are capable of assembling a variety of membrane-associated proteins and signaling molecules in short-lived functional units. Here, we review PDZ proteins that participate in the regulation of signaling, trafficking, and function of G protein-coupled receptors. Salient structural features of PDZ proteins that allow them to recognize targeted GPCRs are considered. Scaffolding proteins harboring PDZ domains may contain single or multiple PDZ modules and may also include other protein-protein interaction modules. PDZ proteins may impact receptor signaling by diverse mechanisms that include retaining the receptor at the cell membrane, thereby increasing the duration of ligand binding, as well as importantly influencing GPCR internalization, trafficking, recycling, and intracellular sorting. PDZ proteins are also capable of modifying the assembled complex of accessory proteins such as β-arrestins that themselves regulate GPCR signaling. Additionally, PDZ proteins may modulate GPCR signaling by altering the G protein to which the receptor binds, or affect other regulatory proteins that impact GTPase activity, protein kinase A, phospholipase C, or modify downstream signaling events. Small molecules targeting the PDZ protein-GPCR interaction are being developed and may become important and selective drug candidates.

Na/H exchanger regulatory factors control parathyroid hormone receptor signaling by facilitating differential activation of G(alpha) protein subunits

The Na/H exchanger regulatory factors, NHERF1 and NHERF2, are adapter proteins involved in targeting and assembly of protein complexes. The parathyroid hormone receptor (PTHR) interacts with both NHERF1 and NHERF2. The NHERF proteins toggle PTHR signaling from predominantly activation of adenylyl cyclase in the absence of NHERF to principally stimulation of phospholipase C when the NHERF proteins are expressed. We hypothesized that this signaling switch occurs at the level of the G protein. We measured G protein activation by [(35)S]GTPgammaS binding and G(alpha) subtype-specific immunoprecipitation using three different cellular models of PTHR signaling. These studies revealed that PTHR interactions with NHERF1 enhance receptor-mediated stimulation of G(alpha)(q) but have no effect on stimulation of G(alpha)(i) or G(alpha)(s). In contrast, PTHR associations with NHERF2 enhance receptor-mediated stimulation of both G(alpha)(q) and G(alpha)(i) but decrease stimulation of G(alpha)(s). Consistent with these functional data, NHERF2 formed cellular complexes with both G(alpha)(q) and G(alpha)(i), whereas NHERF1 was found to interact only with G(alpha)(q). These findings demonstrate that NHERF interactions regulate PTHR signaling at the level of G proteins and that NHERF1 and NHERF2 exhibit isotype-specific effects on G protein activation.

Regulation of parathyroid hormone type 1 receptor dynamics, traffic, and signaling by the Na+/H+ exchanger regulatory factor-1 in rat osteosarcoma ROS 17/2.8 cells

The effects of the expression of the Na+/H+ exchanger regulatory factor-1 (NHERF1) on the distribution, dynamics, and signaling properties of the PTH type 1 receptor (PTH1R) were studied in rat osteosarcoma cells ROS 17/2.8. NHERF1 had a dramatic effect on the subcellular distribution of PTH1R, promoting a substantial relocation of the receptor to regions of the plasma membrane located in very close proximity to cytoskeletal fibers. Direct interactions of NHERF1 with the PTH1R and the cytoskeleton were required for these effects, because they were abolished by 1) PTH1R mutations that impair NHERF1 binding, and 2) NHERF1 mutations that impair binding to the PTH1R or the cytoskeleton. NHERF1 reduced significantly the diffusion of the PTH1R by a mechanism that was also dependent on a direct association of NHERF1 with the PTH1R and the cytoskeleton. NHERF1 increased ligand-dependent production of cAMP and induced ligand-dependent rises in intracellular calcium. These effects on calcium were due to increased calcium uptake, as they were blocked by calcium channel inhibitors and by the addition of EGTA to the medium. These calcium effects were abolished by protein kinase A inhibition but phospholipase C inhibition was without effect. Based on these analyses, we propose that, in ROS cells, the presence of NHERF1 induces PTH-dependent calcium signaling by a cAMP-mediated mechanism that involves local protein kinase A-dependent activation of calcium channels.

Parathyroid hormone and leptin--new peptides, expanding clinical prospects

There are three injectable and one oral bone-building (i.e., bone anabolic) parathyroid hormone (PTH) peptides. One of the four, Lilly's injectable teriparatide (Forteo), is currently being used, and the other three are in clinical trials. They are being used or assessed only for treating postmenopausal osteoporosis. However, their potential clinical targets now extend far beyond osteoporosis. They can accelerate the mending of even severe non-union fractures; they will probably be used to strengthen the anchorage of pros-theses to bone; they have been shown to treat psoriasis that has resisted other treatments; they can increase the size of haematopoietic stem cell proliferation and accelerate the endogenous repopulation or repopulation by donor transplants of bone marrow depleted by chemotherapeutic drugs; and they may prevent vascular ossification. Leptin, a member of the cytokine superfamily has a PTH-like osteogenic activity and may even partly mediate PTH action. But leptin has two drawbacks that cloud its therapeutic future. First, apart from directly stimulating osteoblastic cells, it targets cells in the hypothalamic ventromedial nuclei and through them it reduces oestrogenic activity by promoting osteoblast-suppressing adrenergic activity. Second, it stimulates vascular and heart valve ossification, which leads to such events as heart failure and diabetic limb amputations.

PTH revisited11This paper is dedicated to Professor Thomas E. Andreoli. Pigmæi gigantum humeris impositi plusquam ipsi gigantes vident.22Original studies were supported by National Institutes of Health grant DK-54171

Recent investigations of parathyroid hormone (PTH) have advanced our understanding of its circulating forms as well as its action. It is now clear that first-generation immunoradiometric assays of so-called intact "PTH" not only measured full-length PTH(1-84) but also recognized large PTH fragments lacking the amino-terminus. New, second generation assays detect only full-length PTH. Under diverse pathological settings, second generation assays display lower levels of PTH (1-84). By measuring full-length PTH (bioactive PTH) and the combined full-length plus amino-terminal PTH fragments, the amount of non-PTH(1-84) in circulation can be estimated. The primary amino-terminal fragment is likely to be PTH(7-84). A considerable controversy surrounds the pathological significance of PTH(7-84) and its relation to adynamic bone disease. While these findings were emerging, other work uncovered the apparent basis by which PTH receptors signal through cAMP in some instances but through Ca/inositol phosphate in others. This signaling switch is dictated by the cytoplasmic adapter protein NHERF1 (EBP50), which is expressed in a cell-selective fashion. Other provocative findings may provide a means of unifying determinations of PTH(7-84) with the effects of NHERF1 on PTH receptor signaling. These latter studies reveal that in cells expressing NHERF1, PTH(7-84) has no effect on PTH receptor signaling or internalization. However, in cells lacking or expressing low levels of NHERF1, PTH(7-84) internalizes the PTH receptor without accompanying activation. Together, these findings suggest that the accumulation of PTH(7-84) in renal failure may lead to PTH resistance by internalizing and down-regulating PTH receptors.

PTH-1R responses to PTHrP and regulation by vitamin D in keratinocytes and adjacent fibroblasts

Vitamin D and PTHrP are essential for the differentiation of keratinocytes and epidermal development. The action of PTHrP on skin is mediated via its PTH-1R receptors present in both epidermal and dermal cells. This suggests that PTHrP may have a paracrine/autocrine role, and its receptors may act in association or in negative cooperativity. We compared the intracellular signaling pathways in response to PTHrP (1-34) and to various PTHrP peptides, the N-terminal (1-34), Mid region (67-89), and C-terminal (107-139) fragments, and the possible modulation of PTHrP and its receptor mRNA expressions by vitamin D. Adjacent dermal fibroblasts as freshly isolated keratinocytes expressed both PTHrP and PTH-1R mRNAs, and responded to the various PTHrP fragments. bPTH and PTHrP(1-34) increased both cellular cAMP and [Ca(2+)]i in keratinocytes and fibroblasts. In contrast, PTHrP (107-139) increased [Ca(2+)]i but not cAMP in the two cell types. PTHrP (67-89) had no effect in keratinocytes, and only increased [Ca(2+)]i in fibroblasts. Vitamin D deficiency in weaned rats increased the expression of PTHrP mRNA in keratinocytes, and decreased it in fibroblasts and kidneys. Vitamin D deficiency increased PTH-1R mRNA expression in keratinocytes and kidneys, but not in fibroblasts. Although keratinocytes and skin fibroblasts are target cells for PTHrP and express PTH-1R, the two adjacent cell types differ as regards their intracellular signaling in response to PTHrP peptides. Moreover vitamin D regulates PTHrP and PTH-1R in a cell-specific manner.

Taming psoriatic keratinocytes?PTHs' uses go up another notch

The native parathyroid hormone (PTH) and several of its N-terminal adenylyl cyclase-activating fragments and their analogs have become the star stimulators of bone growth for treating osteoporosis, accelerating fracture healing, and strengthening the anchorage of prosthetic bone implants and one of them (Lilly's Forteo--recombinant hPTH-(1-34) has recently arrived in the clinic. But something entirely different has been lurking in the background-the ability of the adenylyl cyclase stimulating hPTH-(1-34) to calm hyperproliferating keratinocytes and reduce psoriatic lesions. By contrast PTH-(7-34) which cannot stimulate adenylyl cyclase actually stimulates keratinocyte proliferation. Normal keratinocytes make PTHrP after they lift off the basal lamina and have stopped cycling. But they have an unconventional PTH/PTHrP receptor which is not coupled to adenylyl cyclase. Psoriatic keratinocytes do not make PTHrP and have only a broken-down, proliferation-limiting terminal differentiation-driving Notch-Notch ligand mechanism. Putting these and other facts together produces a possible picture of an exogenously applied adenylyl cyclase-activating PTH pinch hitting for the missing PTHrP and restoring normal keratinocyte proliferative activity epidermal structure by stimulating dermal fibroblasts which do have the conventional adenylyl cyclase-linked PTHR1 and in response directly or indirectly restore the overlying basal keratinocytes' Notch-Notch ligand terminal differentiation-driving mechanism and consequently a normal epidermal structure.

Regulation of the 25-hydroxyvitamin D-1alpha-hydroxylase gene and its splice variant

The 25-hydroxyvitamin D-1alpha-OHase (1alpha-OHase) is responsible for producing the active form of vitamin D, 1alpha,25-dihydroxyvitamin D. The enzyme not only is expressed in kidneys, but also is expressed in many nonrenal tissues, including skin. In this study, we compared the regulation of the 1alpha-OHase expression in kidney cells and keratinocytes. Using transfected luciferase reporter gene constructs, we compared the activity and regulatory features of the human 1alpha-OHase gene promoter in C-21 human kidney cells (PTH/PTHrP receptor positive) and cultured human keratinocytes (NHKs). We found that two regions, -1,100 bp and -396 bp from the ATG, were highly sensitive to parathyroid hormone (PTH) in C-21 cells but not in NHK. Furthermore, three CRE-like sequences (CLS) were identified within this PTH-sensitive area of the 1alpha-OHase promoter and when deleted they reduced induction of PTH by 50%-95% in C-21 cells. To further investigate the differential regulation profile, we examined the protein products of 1alpha-OHase in kidney and skin. Western blot analysis of whole cell extracts from these tissues with a 1alpha-OHase-specific antibody revealed the predicted 1alpha-OHase protein product of 56 kDa in kidney and a larger protein product of 59 kDa in skin. Using RT-PCR for the 1alpha-OHase in skin and kidney, we detected an insertion between exons 2 and 3 in skin but not in kidney. These results suggest that the regulation of renal and skin 1alpha-OHase gene expression may be tissue specific and possibly produce different splice variants, and that this specificity is likely conferred by differential expression of CRE-binding proteins in different cell types. In conclusion, the differential tissue expression of 1alpha-OHase gene variants and the tissue-specific regulation profile open up a new paradigm in the understanding of the role of 25-hydroxyvitamin D3 1alpha-hydroxylase gene in the regulation of vitamin D physiology.

Parathyroid hormone-related peptide modulates signal pathways in skin and hair follicle cells

Parathyroid hormone-related protein (PTHrP) is secreted by skin epithelial cells and is thought to play an important role in the development and function of the hair follicle. It was hypothesized that PTHrP binds to receptors in dermal papilla cells and modulates intracellular signaling systems in these cells. We tested the effects of PTHrP on protein synthesis, protein kinase A (PKA) and protein kinase C (PKC) activities as well as tyrosine phosphorylation in rat vibrissa dermal papilla and capsular fibroblast cells. Cells were cultured in the presence or absence of the N-terminal peptide PTHrP1-34 for 48 h and detergent extracts prepared. Proteins were separated by electrophoresis. Phosphotyrosine and the PTH/PTHrP receptor immunoreactivity was identified by Western blot analysis. PKC and PKA activities in the cells were measured using colorimetric enzyme assays. Extracts of both dermal papilla cells and capsular fibroblasts displayed immunoreactivity to the PTH/PTHrP receptor. Electrophoresis showed that PTHrP treatment reduced the density of a 50-kDa protein in dermal papilla cells but not in capsular fibroblasts. Media conditioned by the cells showed similar changes, indicating that the PTHrP-modulated 50-kDa protein was secreted. Furthermore, 2-D gel electrophoresis indicated that the protein had a number of phosphorylation sites. Western analysis with antiphosphotyrosine antibodies confirmed a significant decrease in the intensity of a phosphorylated 50-kDa protein in papilla cells and papilla cell-conditioned medium. PKC and PKA activities of papilla cells were unaffected by PTHrP. However, activities of PKC were increased and PKA reduced in capsular fibroblasts following peptide treatment. These cell-specific effects showed that endogenous PTHrP may activate different intracellular pathways in mesenchymal cells of skin and elicit changes in levels of locally secreted proteins that specifically modulate normal follicular function.

Functional type I PTH/PTHrP receptor in freshly isolated newborn rat keratinocytes: identification by RT-PCR and immunohistochemistry

The presence of identical or distinct type I parathyroid hormone (PTH)/parathyroid hormone-related peptide (PTHrP) receptors in keratinocytes is still a matter of debate. We studied the expression and functionality of PTHrP receptors in freshly isolated keratinocytes from newborn rat skin. Four overlapping primers, amplifying different regions in the rat PTH receptor, were used for reverse transcriptase-polymerase chain reaction (RT-PCR). The first region corresponded to the N-terminal extracellular region and the first transmembrane domain (S/M1), the second region amplified the connecting intracellular and extracellular loops transmembrane domain (E2/M5), the third spanned the range from the transmembrane to the intracellular domain (M4/T), and the fourth region amplified the C-terminal tail (M6/7/T). The PCR products from the keratinocyte RNA were identical to those from kidney RNA of the same rats. The cloned four transcripts showed 100% of homologies with the cDNA sequence from bone ROS cells. Keratinocytes, freshly isolated or present in situ in the epidermis, recognized an anti-PTH receptor antibody (PTH-II) directed against the receptor extracellular domain. Western blotting showed the same protein patterns in keratinocytes, kidney, and ROS cell extracts. Low doses of PTHrP(1-34) (10(-12)-10(-9) M) increased the cell number studied by [3H]thymidine incorporation and DNA content. Treatment with the PTH/PTHrP receptor antagonist [Asn10, Leu11, D Trp12] PTHrP(7-34) or two different PTH receptor antibodies inhibited the increase in cell proliferation induced by PTHrP(1-34). All these findings indicate that newborn rat epidermis and keratinocytes express functional PTHrP receptors, which are identical to type I PTH/PTHrP receptor and are recognized by PTHrP(1-34).

Expression of parathyroid hormone (PTH)/PTH-related peptide receptor messenger ribonucleic acid in mice hair cycle

There is increasing evidence that parathyroid hormone (PTH) and PTH-related peptide (PTHrP) are involved in normal skin cell growth, influence the proliferation and differentiation of the epidermis and hair follicle. PTHrP and PTH/PTHrP receptor show prominent cutaneous expression, may exert important paracrine and/or autocrine functions. The expression of PTH/PTHrP receptor in different stages of hair cycle is unknown. Therefore, we examined the amount of PTH/PTHrP mRNA in C57BL/6 mice skin at different stages of hair cycle by relatively quantitative reverse transcription-polymerase chain reaction (RT-PCR), and investigated the localization of this receptor in mice skin by in situ hybridization. The expression of PTH/PTHrP receptor mRNA were higher in anagen, but significantly lower in catagen and telogen. Then, the PTH/PTHrP receptor mRNA was located in the inner root sheath (IRS) in anagen and catagen, but was not detected in telogen hair follicles, although it was expressed weakly in dermis. The variety of the PTH/PTHrP receptor mRNA expression during hair cycling suggest that PTH, PTHrP and their receptors might participate in the regulation of hair cycle in mice skin.

Parathyroid hormone-related peptide regulation of chick tibial growth plate chondrocyte maturation requires protein kinase A

Regulation of phenotype in chick tibial growth plate chondrocytes (GPCs) by parathyroid hormone-related peptide (PTHrP) is facilitated via signaling through three pathways: protein kinase A (PKA), protein kinase C (PKC) and inositol-1,4,5-trisphosphate-induced Ca2+ transients. To establish the underlying signaling specificity for PTHrP-regulation of chondrocyte maturation, we examined the separate involvement of each of these three pathways in the PTHrP regulation of key hallmarks of GPC phenotype: stimulation of proliferation and proteoglycan synthesis and reduction of alkaline phosphatase activity and type X collagen expression. Mimicking the PTHrP stimulation either of PKC with 1-oleoyl 2-acetyl glycerol or of a Ca2+ pulse with 65 mM KCl did not lead to PTHrP-like effects on any of the four markers examined. Also, inhibition of PKC with myr-psiPKC or blockade of Ca2+ signals with an intracellular chelator did not inhibit PTHrP action. However, PKA activation with dibutyryl cAMP mimicked PTHrP and blockade of PTHrP stimulation of PKA with H-89 inhibited the regulatory action of the factor. These data demonstrate that although activation of PKC or Ca2+ signals is not required, the cylic AMP-dependent A kinase is required for PTHrP to regulate key hallmarks of GPC phenotype.

Effect of parathyroid hormone-related protein on fibroblast proliferation and collagen metabolism in human skin

The parathyroid hormone-related protein (PTHrp), structurally similar to the parathyroid hormone (PTH) in its NH(2)-terminal part, was first identified as a tumour-derived peptide responsible for a paraneoplastic syndrome known as humoral hypercalcemia of malignancy. The PTHrp gene is expressed not only in cancer but also in normal tissues during adult and/or fetal life, where it plays predominantly paracrine and/or autocrine roles. In the skin PTHrp produced by keratinocytes acts on fibroblasts by complex cooperative circuits involving cytokines and growth factors. In this report, we studied the direct effects of synthetic PTHrp 1-40 on proliferation and collagen synthesis and matrix metalloproteinase-2 (MMP-2) activity in cultures of fibroblasts isolated from normal human skin. Fibroblasts exposure to varying doses of PTHrp for 48 h, significantly and dose-dependently inhibited proliferation evaluated by [(3)H]-thymidine incorporation into DNA. A dose-dependent stimulation of cAMP released into the medium was concomitantly observed. In contrast, PTHrp had no effect on collagen synthesis evaluated either by [(3)H]-proline incorporation or by radioimmunoassay (RIA) of the carboxyterminal fragment of type I procollagen (PICP). MMP-2 activity, evaluated by quantitative zymographic analysis, was significantly increased by PTHrp treatment at doses of 160 and 320 nM. These findings indicate that PTHrp may play a role in normal dermal physiology by controlling both fibroblast proliferation and extracellular matrix degradation.

Stimulation of protein kinase C activity in cells expressing human parathyroid hormone receptors by C- and N-terminally truncated fragments of parathyroid hormone 1-34

The parathyroid hormone (PTH) fragment PTH(1-34) stimulates adenylyl cyclase, phospholipase C (PLC), and protein kinase C's (PKCs) in cells that express human, opossum, or rodent type 1 PTH/PTH-related protein (PTHrP) receptors (PTHR1s). Certain carboxyl (C)-terminally truncated fragments of PTH(1-34), such as human PTH(1-31) [hPTH-(1-31)NH2], stimulate adenylyl cyclase but not PKCs in rat osteoblasts or PLC and PKCs in mouse kidney cells. The hPTH(1-31)NH2 peptide does fully stimulate PLC in HKRK B7 porcine renal epithelial cells that express 950,000 transfected hPTHR1s per cell. Amino (N)-terminally truncated fragments, such as bovine PTH(3-34) [bPTH(3-34)], hPTH(3-34)NH2, and hPTH(13-34), stimulate PKCs in Chinese hamster ovary (CHO) cells expressing transfected rat receptors, opossum kidney cells, and rat osteoblasts, but an intact N terminus is needed to stimulate PLC via human PTHR1s in HKRK B7 cells. We now report that the N-terminally truncated analogs bPTH(3-34)NH2 and hPTH(13-34)OH do activate PKC via human PTHR1s in HKRK B7 cells, although less effectively than hPTH(1-34)NH2 and hPTH(1-31)NH2. Moreover, in a homologous human cell system (normal foreskin fibroblasts), these N-terminally truncated fragments stimulate PKC activity as strongly as hPTH(1-34)NH2 and hPTH(1-31)NH2. Thus, it appears that unlike their opossum and rodent equivalents, hPTHR1s can stimulate both PLC and PKCs when activated by C-terminally truncated fragments of PTH(1-34). Furthermore, hPTHR1s, like the PTHR1s in rat osteoblasts, opossum kidney cells, and rat PTHR1-transfected CHO cells also can stimulate PKC activity by a mechanism that is independent of PLC. The efficiency with which the N-terminally truncated PTH peptides stimulate PKC activity depends on the cellular context in which the PTHR1s are expressed.

New members of the parathyroid hormone/parathyroid hormone receptor family: the parathyroid hormone 2 receptor and tuberoinfundibular peptide of 39 residues

The parathyroid hormone (PTH) family currently includes three peptides and three receptors. PTH regulates calcium homeostasis through bone and kidney PTH1 receptors. PTH-related peptide, probably also through PTH1 receptors, regulates skeletal, pancreatic, epidermal, and mammary gland differentiation and bladder and vascular smooth muscle relaxation and has a CNS role that is under investigation. Tuberoinfundibular peptide of 39 residues (TIP39) was recently purified from bovine hypothalamus based on selective PTH2 receptor activation. PTH2 receptor expression is greatest in the CNS, where it is concentrated in limbic, hypothalamic, and sensory areas, especially hypothalamic periventricular neurons, nerve terminals in the median eminence, superficial layers of the spinal cord dorsal horn, and the caudal part of the sensory trigeminal nucleus. It is also present in a number of endocrine cells. Thus TIP39 and PTH2 receptor-influenced functions may range from pituitary and pancreatic hormone release to pain perception. A third PTH-recognizing receptor has been found in zebrafish.

Neuroendocrinology of the skin

The classical observations of the skin as a target for melanotropins have been complemented by the discovery of their actual production at the local level. In fact, all of the elements controlling the activity of the hypothalamus-pituitary-adrenal axis are expressed in the skin including CRH, urocortin, and POMC, with its products ACTH, alpha-MSH, and beta-endorphin. Demonstration of the corresponding receptors in the same cells suggests para- or autocrine mechanisms of action. These findings, together with the demonstration of cutaneous production of numerous other hormones including vitamin D3, PTH-related protein (PTHrP), catecholamines, and acetylcholine that share regulation by environmental stressors such as UV light, underlie a role for these agents in the skin response to stress. The endocrine mediators with their receptors are organized into dermal and epidermal units that allow precise control of their activity in a field-restricted manner. The skin neuroendocrine system communicates with itself and with the systemic level through humoral and neural pathways to induce vascular, immune, or pigmentary changes, to directly buffer noxious agents or neutralize the elicited local reactions. Therefore, we suggest that the skin neuroendocrine system acts by preserving and maintaining the skin structural and functional integrity and, by inference, systemic homeostasis.

Identification of a novel parathyroid hormone-responsive gene in human osteoblastic cells

Parathyroid hormone (PTH) is a potent stimulator of osteoblastic cell function in vitro and bone resorption and formation in vivo; however, the details of the molecular mechanism(s) responsible for PTH action and the regulation of gene expression in response to PTH remain unknown. In this study, we employed an mRNA differential display (DRD) approach to examine the initial events in gene expression in human osteoblast-like SaoS-2/B10 cells exposed to 10(-7) mol/L bPTH(1-34). This approach identified several differentially regulated mRNA species, including a novel paired-class homeobox protein, osteoblast-specific factor-2 (OSF-2), and a unique clone with no known sequence homology (clone G18). G18 is a previously unidentified human gene, expressed in a wide variety of human tissues, including heart, brain, placenta, skeletal muscle, and kidney, and is regulated by PTH in osteoblastic cells in vitro. This mRNA appears to be the product of a single gene, which is alternatively spliced to produce multiple transcript sizes observed in several tissues, except bone and bone-derived cells, in which a single predominant approximately 1.8 kb transcript is observed. Our study has identified several genes that have expression altered significantly by treatment with bPTH(1-34), and which may provide insight into the immediate effects of PTH on osteoblast-like cells and ultimately on the mechanism of action and bioactivity of PTH.

Stimulation of membrane-associated protein kinase-C activity in spleen lymphocytes by hPTH-(1-31)NH2, its lactam derivative, [Leu27]-cyclo(Glu22-Lys26)-hPTH-(1-31)NH2, and hPTH-(1-30)NH2

Human parathyroid hormone, hPTH-(1-34), stimulates adenylyl cyclase and phosphatidylinositol-bisphosphate-specific phospholipase-C (PIP2-PLC), as indicated by increased membrane-associated protein kinase C (PKC) activity in ROS 17/2 rat osteosarcoma cells. The C-terminally truncated hPTH-(1-31)NH2 stimulates adenylyl cyclase as strongly as hPTH-(1-34) in these cells, but it does not stimulate PKC activity. Even [Leu27]-cyclo(Glu22-Lys26)-hPTH-(1-31)NH2, a 6-fold stronger adenylyl cyclase stimulator than hPTH-(1-34), cannot stimulate PKC activity in ROS cells. Therefore PTH required its 32-34 region to stimulate PIP2-PLC/PKCs in this osteosarcoma line. In contrast, hPTH-(1-31)NH2 [Leu27]-cyclo(Glu22-Lys26)-hPTH-(1-31)NH2 and even hPTH-(1-30)NH2 can stimulate PKC activity in freshly isolated rat spleen lymphocytes as strongly as hPTH-(1-34)NH2. The difference in the ability of membrane-associated PKC activity in spleen lymphocytes, but not in ROS cells, to be stimulated by C-terminally truncated PTH fragments might be due to different receptor densities or to the lymphocyte's atypical PTH/PTHrP receptor.

Cell-specific signaling and structure-activity relations of parathyroid hormone analogs in mouse kidney cells

PTH is an 84-amino acid protein. Occupancy of its cognate receptor generally results in activation of adenylyl cyclase and/or phosphoinositide-specific phospholipase Cbeta (PLCbeta). In the kidney, PTH receptors are present on proximal and distal tubule cells. In proximal tubules, PTH induces calcium signaling, typified by a transient rise in intracellular calcium ([Ca2+]i) and inositol trisphosphate formation, but does not affect calcium absorption. By contrast, in distal tubules, PTH increases calcium absorption that is associated with a slow and sustained rise in [Ca2+]i, but does not stimulate phospholipase C (PLC) or cause inositol trisphosphate accumulation. Nonetheless, stimulation of distal calcium transport requires activation of protein kinase C (PKC) and protein kinase A. We now characterize the origin of the differential effects of ligand occupancy by using synthetic human PTH analogs that preferentially activate adenylyl cyclase and/or PLCbeta. We further tested the hypothesis that phospholipase D is responsible for PKC activation in distal tubule cells. PTH-(1-31) increased [Ca2+]i in distal tubule but not in proximal tubule cells, whereas PTH-(3-34) caused a partial increase in [Ca2+]i in proximal cells, but had no effect in distal cells. PTH-(7-34) blocked increases in [Ca2+]i in distal tubule cells stimulated by PTH-(1-34) and PTH-(1-31). The PLC inhibitor U73122 abolished the PTH-induced rise in [Ca2+]i and inositol trisphosphate formation by proximal tubule cells, but had no effect on PTH-stimulated Ca2+ uptake by distal tubule cells. These results support the view that activation of PKC by PTH in distal tubule cells does not involve PLCbeta. PTH did, however, activate phospholipase D with attendant formation of diacylglycerol in distal cells. As activation of PKC is required for induction of calcium transport by PTH, we conclude that PTH receptors are capable of activating multiple phospholipases and that the structural requirements for such activation differ in proximal and distal tubule cells.

Human keratinocytes express transcripts for three isoforms of parathyroid hormone-related protein (PTHrP), but not for the parathyroid hormone/PTHrP receptor: effects of 1,25(OH)2 vitamin D3

Parathyroid hormone-related protein (PTHrP) is strongly expressed in the epidermis and has been implicated in the regulation of growth and differentiation of keratinocytes. PTHrP has N-terminal sequence homology with parathyroid hormone (PTH) and binds to the type I PTH/PTHrP receptor, but earlier reports suggest that keratinocytes do not possess this cell surface receptor. In order to determine which PTHrP mRNA isoforms are expressed by keratinocytes and whether the type I receptor mRNA is present, we designed specific primers for reverse transcriptase-polymerase chain reaction. The interaction of PTHrP with other promoters of keratinocyte differentiation is unclear. In particular, 1,25(OH)2D3 is also fundamental in calcium homeostasis and induces changes in intracellular calcium. We therefore investigated the effect of 1,25(OH)2D3 on PTHrP mRNA expression and protein production in cultured human keratinocytes. Cells were incubated for 3 days at concentrations of 1.25(OH)2D3 of 10(-10)-10(-6) mol/L. PTHrP in culture supernatant, measured by two site immunoradiometric assay, was 915 +/- 98 PTHrP fmol/mg of cell layer protein in untreated cultures decreasing to 570 +/- 113 with 10(-8) mol/L and 402 +/- 24 with 10(-6) mol/L 1,25(OH)2D3 (mean +/- SEM, P < 0.01, n = 6). Transcripts for all three PTHrP isoforms (139, 141 and 173 amino acids) were detectable in keratinocyte mRNA. Corresponding to the decrease in PTHrP protein we demonstrated a reduction in all three PTHrP mRNA transcripts after 3 days' incubation with 1,25(OH)2D3 over a concentration range 10(-10)-10(-6) mol/L. Repeated studies failed to detect type I PTH/PTHrP receptor mRNA in human keratinocytes, either in control cultures or in the presence of 1,25(OH)2D3. We have shown that keratinocytes produce abundant PTHrP and that this is modulated by 1,25(OH)2D3, suggesting a physiological role. Further studies are required to investigate the relative expression of PTHrP isoforms, their role in keratinocyte signalling and the receptors involved.

Functional expression and signaling properties of cloned human parathyroid hormone receptor in Xenopus oocytes. Evidence for a novel signaling pathway

Expression of human parathyroid hormone receptor (hPTHR) was obtained in Xenopus oocytes. Receptor function was detected by hormone stimulation of endogenous Ca2+-activated Cl- current. This current was blocked by injected, but not by extracellular, EGTA, confirming that the hPTHR activates cytosolic Ca2+ signaling pathways. PTH responses were acutely desensitized but were regained in 6 12 h. Injection of cAMP or analogues had no effect on either responsiveness or desensitization to hPTH. The hPTH response was more sluggish than seen with serotonin 5-hydroxytryptamine (5-HT2C) receptor. In oocytes co-expressing both hPTHR and 5-HT2C receptors, homologous desensitization was seen, but cross-desensitization was not observed. Injection of inositol 1,4,5-trisphosphate (InsP3) elicited a fast inward current similar to that induced by serotonin, and complete cross-desensitization occurred between the InsP3 and 5-HT2C responses. Desensitization by hPTH did not affect responses to either InsP3 or serotonin, but cells desensitized to injected InsP3 still responded strongly to PTH. Oocytes did not respond to either cADPR or NAADP+, but NADP+ and analogues were found to be potent inhibitors of PTH signaling. We suggest that PTH cytosolic Ca2+ signaling in oocytes either involves a novel signaling system or proceeds through a Ca2+ compartment whose responsiveness is regulated in a novel way.

Distribution and functions of parathyroid hormone-related protein in vertebrate cells

Parathyroid hormone-related protein (PTHrP) was isolated from tumors and identified as the agent of humoral hypercalcemia of malignancy (HHM) in 1987. Since then its gene structure in several mammalian and an avian species has been analyzed and its gene expression demonstrated in many adult and embryonic tissues derived from all three germ layers. The composition and structure of PTHrP peptide depends on both differential gene splicing and posttranslational processing, which result in a range of peptides of potentially diverse functions. This chapter describes the distribution of PTHrP in both normal and neoplastic adult and embryonic tissues. PTHrP is of fundamental importance to cell survival because the absence of the gene is fatal; this aspect of PTHrP function in cell physiology becomes overwhelmingly important in neoplasia. Intracrine or paracrine actions for PTHrP seem to be most likely in mammalian and avian physiology, but in fishes high circulating levels suggest classic endocrine functions as well. Much remains to be learned of the biology of this fascinating protein.

C-terminal fragment of parathyroid hormone-related protein, PTHrP-(107-111), stimulates membrane-associated protein kinase C activity and modulates the proliferation of human and murine skin keratinocytes

Low concentrations of the C-terminal parathyroid hormone-related protein (PTHrP) fragments, PTHrP-(107-111) and PTHrP-(107-139), stimulated membrane-associated protein kinase Cs (PKCs), but not adenylyl cyclase or an internal Ca2+ surge, in early passage human skin keratinocytes and BALB/MK-2 murine skin keratinocytes. The fragment maximally stimulated membrane-associated PKCs in BALB/MK-2 cells at 5 x 10(-9) to 10(-8) M. The maximally PKC-stimulating concentrations of PTHrP-(107-111) also stopped or stimulated BALB/MK-2 keratinocyte proliferation depending on whether the cells were, respectively, cycling or quiescent at the time of exposure. Thus, just one brief (30-minute) pulse of 10(-8) M PTHrP-(107-111) stopped the proliferation of BALB/MK-2 keratinocytes for at least 5 days. On the other hand, daily 30-minute pulses of 10(-8) M PTHrP-(107-111) started and then maintained the proliferation of initially quiescent BALB/MK-2 cells. Similarly PTHrP-(107-111) inhibited DNA synthesis by cycling primary adult human keratinocytes, but it stimulated DNA synthesis by quiescent human keratinocytes.

Mechanisms of 1S,3R-ACPD-induced neuroprotection in rat hippocampal slices subjected to oxygen and glucose deprivation

The efficacy and mechanisms of 1-amino-cyclopentyl-1S,3R-dicarboxylate (1S,3R-ACPD)-induced neuroprotection were investigated in rat hippocampal slices subjected to 10 min of oxygen and glucose deprivation. Neuronal viability was assessed by measuring both the amplitude of evoked population spike in the CA1 pyramidale and by imaging CA1 neurons using a live/dead fluorescence assay with confocal microscopy. CA1 pyramidal neurons in oxygen-glucose deprived slices remained viable for up to 120 min following the insult but were dead by 240 min. Pretreatment with 1S,3R-ACPD significantly protected the oxygen-glucose deprived slices in a concentration-dependent fashion. Oxygen-glucose deprived slices pretreated for the same period with the protein kinase C (PKC) activation phorbol 12-myristate 13-acetate (PMA; 1 microM) were significantly protected whereas oxygen-glucose deprived slices treated with the adenylyl cyclase activator, forskolin (30 microM) were not. Oxygen-glucose deprivation induced a rapid and persistent decrease (approximately 50%) in PKC activity and a > 6 fold increase in cyclic adenosine monophosphate (cAMP) levels in whole hippocampal slices. While 1S,3R-ACPD did not stimulate PKC activity and had no effect on basal cAMP in whole slices, it significantly enhanced the rate of return of cAMP to basal levels following reperfusion. Consistent with this observation, the 1S,3R-ACPD-induced neuroprotection was inhibited by forskolin (30 microM). These results suggest that in vitro neuroprotection of CA1 neurons by 1S,3R-ACPD involves metabotropic glutamate receptors negatively linked to cAMP and possibly those which increase PKC activity.

Ca2+ x calmodulin prevents myristoylated alanine-rich kinase C substrate protein phosphorylation by protein kinase Cs in C6 rat glioma cells

Ionomycin stimulated membrane-associated protein kinase Cs (PKCs) activity in C6 rat glioma cells as much as the potent PKCs stimulator 12-O-tetradecanoyl phorbol 13-acetate (TPA). However, while TPA, as expected, powerfully stimulated the phosphorylation of the PKCs' 85-kDa myristoylated alanine-rich protein kinase C substrate (MARCKS) protein, ionomycin unexpectedly did not. Instead, ionomycin reduced the basal MARCKS phosphorylation. Pretreating the glioma cells with ionomycin prevented TPA-stimulated PKCs from phosphorylating the MARCKS protein. The stimulation of membrane PKCs activity and the prevention of MARCKS phosphorylation by ionomycin required external Ca2+ because they were both abolished by adding 5 mM EGTA to the culture medium. Recently (Chakravarthy, B. R., Isaacs, R. J., Morley, P., Durkin, J. P., and Whitfield, J. F. (1995) J. Biol. Chem. 270, 1362-1368), we proposed that Ca2+ x calmodulin complexes block MARCKS phosphorylation by the activated PKCs in keratinocytes stimulated by raising the external Ca2+ concentration. In the present experiments calmodulin prevented MARCKS phosphorylation by TPA-stimulated PKCs in glioma cell lysates, and this blockade was lifted by a calmodulin antagonist, the calmodulin-binding domain peptide. But, physiologically more significant, pretreating intact glioma cells with a cell-permeable calmodulin antagonist, calmidazolium, prevented ionomycin from blocking MARCKS phosphorylation by PKCs in unstimulated and TPA-stimulated cells. The effect of ionomycin on MARCKS phosphorylation was not due to the stimulation of Ca2+ x calmodulin-dependent phosphoprotein phosphatase, calcineurin, because cyclosporin A, a potent inhibitor of this phosphatase, did not stop ionomycin from preventing MARCKS phosphorylation. The ability of ionomycin to prevent TPA-stimulated PKCs from phosphorylating MARCKS depended on whether ionomycin was added before, with, or after TPA. Maximum blockade occurred when ionomycin was added before TPA but was less effective when added with or after TPA. These results indicate that Ca2+ x calmodulin can profoundly affect PKCs' signaling at the substrate level.

Effect of parathyroid hormone and calcitonin on cholinergic markers in rat parathyroid gland

The effect of parathyroid hormone (PTH) and calcitonin on 3H-choline uptake and on 3H-acetylcholine synthesis by rat parathyroid glands were examined. Incubation of tissue for 120 min with PTH or calcitonin resulted in an inverted bell-shaped, dose-dependent inhibition of 3H-choline uptake, with a maximal effect at 10(-9) M concentration. The effect of PTH on parathyroid choline uptake was blunted by preincubation with the PTH antagonist NLe(8-18)-PTH (3-34) amide. PTH brought about a dose-dependent inhibition of 3H-choline conversion to 3H-acetylcholine, with significant effects at 10(-8) M concentration or higher. This inhibitory effect of PTH on 3H-acetylcholine synthesis was blocked by co-incubation with the PTH antagonist NLe(8-18)-PTH (3-34) amide. Only at a 10(-7) M concentration calcitonin was effective to impair the in vitro conversion of radioactive choline into 3H-acetylcholine by parathyroid fragments. The results indicate that, in vitro, PTH, and to a less extent, calcitonin, inhibit cholinergic activity in rat parathyroid glands.

Parathyroid hormone induces protein kinase C but not adenylate cyclase in adult cardiomyocytes and regulates cyclic AMP levels via protein kinase C-dependent phosphodiesterase activity

Adult ventricular cardiomyocytes have been identified as target cells for parathyroid hormone (PTH) but little is known about its signal transduction in these cells. In the present study the influence of PTH on cyclic AMP accumulation and the activity of protein kinase C (PKC) in cardiomyocytes was evaluated. A mid-regional synthetic fragment of PTH, PTH-(28-48), which exerts a hypertrophic effect on cardiomyocytes, increased the activity of membrane-associated PKC in a dose-dependent manner (1-100 nM). Activated membranous PKC was dependent on Ca2+ and sensitive to an inhibitor of Ca(2+)-dependent isoforms of PKC. When adenylate cyclase was stimulated by the addition of isoprenaline, a beta-adrenoceptor agonist, PTH-(28-48) antagonized cyclic AMP accumulation. This antagonistic effect of PTH-(28-48) could be mimicked by activation of PKC with a phorbol ester and inhibited by isobutylmethylxanthine, a phosphodiesterase inhibitor. An N-terminal synthetic fragment, PTH-(1-34), which includes an adenylate cyclase-activating domain, did not stimulate the accumulation of cyclic AMP in cardiomyocytes. The results demonstrate that in adult cardiomyocytes PTH (1) is able to stimulate PKC, (2) is not able to cause accumulation of cyclic AMP and (3) functionally antagonizes the effect of beta-adrenoceptor stimulation to increase cellular cyclic AMP concentrations via PKC-dependent phosphodiesterase activity.

Large-scale preparation and biological activity of recombinant human parathyroid hormone

Human parathyroid hormone (hPTH) has been bacterially expressed in bioreactors as cro-beta-galactosidase-hPTH fusion protein. We have developed a large-scale purification scheme that exploits the pH-dependent differential solubility of hPTH and a two-step chromatographic procedure. We demonstrate that in a number of assay systems, the recombinant material obtained by this procedure is biologically active.

Stimulation of protein kinase C during Ca(2+)-induced keratinocyte differentiation. Selective blockade of MARCKS phosphorylation by calmodulin

Raising the external Ca2+ concentration from 0.05 to 1.8 mM stimulated membrane-associated protein kinase Cs (PKCs) activity as strongly as the specific PKCs activator, 12-O-tetradecanoyl phorbol-13-acetate (TPA) in BALB/MK mouse keratinocytes. This was indicated by the increased phosphorylation of a PKC-selective peptide substrate, Ac-FKKSFKL-NH2, by membranes isolated from the Ca(2+)- or TPA-stimulated keratinocytes. Raising the external Ca2+ concentration to 1.8 mM also triggered a 4-fold rise in the intracellular free Ca2+ concentration. As reported elsewhere (Moscat, J. Fleming, T. P., Molloy, C. J. Lopez-Barahona, M., and Aaronson, S. A. (1989) J. Biol. Chem. 264, 11228-11235), TPA stimulated the phosphorylation of the PKCs substrate, the 85-kDa myristoylated alanine-rich kinase C substrate (MARCKS) protein, in intact keratinocytes, but Ca2+ did not. Furthermore, Ca(2+)-pretreatment reduced the TPA-induced phosphorylation of the 85-kDa protein in intact cells. There was no significant increase in MARCKS phosphorylation when keratinocytes were treated with a Ca2+.CaM-dependent phosphatase inhibitor, cyclosporin A, before stimulation with 1.8 mM Ca2+.Ca2+.calmodulin suppressed the ability of isolated membranes to phosphorylate the 85-kDa MARCKS holoprotein in vitro in the presence of phosphatase inhibitors such as fluoride, pyrophosphate, and vanadate, and this inhibition was overcome by a calmodulin antagonist, the calmodulin-binding domain peptide. Thus, the ability of 1.8 mM Ca2+ to strongly stimulate the membrane PKCs activity without stimulating the phosphorylation of the MARCKS protein in keratinocytes is consistent with the possibility of Ca2+.calmodulin complexes, formed by the internal Ca2+ surge, binding to, and blocking the phosphorylation of, this PKC protein substrate.

Inactive membrane protein kinase Cs: a possible target for receptor signalling

The activation of the multifunctional cell signalling enzymes, the protein kinase Cs (PKCs), is generally thought to result from the translocation of inactive cytosolic enzymes to activation sites in cell membranes. However, recent studies suggest that PKCs may also be stimulated in cells by processes independent of translocation. One possible mechanism is the modulation of the activity of PKCs already resident in membranes. A PKC assay that measures enzyme activity directly in isolated native membranes has revealed the presence of an activatable pool of PKCs resident in native membranes of various cells and tissues. In 3T3-L1 cells, some or all of this pool of membrane PKCs was stimulated within 10 min of exposing the cells to 10 ng/ml epidermal growth factor or 100 ng/ml fibroblast growth factor. Similar increases in PKC activity were observed in native membranes isolated from CTLL-2, WEHI-231 and S49 lymphoma cells that had been exposed to interleukin-2. These growth factors all stimulated membrane PKC activity without detectably translocating cytosolic enzymes to the membranes. In intact WEHI cells, low concentrations (5-10 microM) of a diacylglycerol, 1-oleoyl-2-acetyl-sn-glycerol (OAG), or low concentrations (2-10 nM) of phorbol 12-myristate 13-acetate sufficed to activate PKCs already resident in membranes, but much higher concentrations (50-100 microM and 50-100 nM respectively) were needed to detectably stimulate the translocation of cytosolic PKCs. A phosphatidylcholine-specific phospholipase C also selectively stimulated membrane PKCs in WEHI cells at concentrations that were much less than those needed to induce the translocation of cytosolic enzymes. Furthermore, interleukin-2 and low concentrations of OAG both stimulated the phosphorylation of the 85 kDa PKC-selective substrate protein in intact WEHI cells in which translocation of PKCs was not evident. These results suggest that the membranes of some cells maintain a pool of activatable PKCs that respond to lower levels of extracellular stimuli than cytosolic PKCs, and that can be stimulated by signals which produce diacylglycerols through the hydrolysis of phospholipids other than polyphosphoinositides.

Parathyroid hormone (PTH) and PTH-related protein stimulate surfactant phospholipid synthesis in rat fetal lung, apparently by a mesenchymal-epithelial mechanism

We examined the effects of parathyroid hormone (PTH) and PTH-related protein (PTHrP) on rat fetal lung fibroblast and pneumocyte cell signalling. We also studied the effects of PTH and PTHrP on surfactant phospholipid synthesis to determine whether these peptides can modulate pulmonary maturation. Exposure of fibroblasts (gestational days 18-21) to PTH(1-34) or PTHrP(1-34) produced time- and dose-dependent stimulations of cAMP and inositol phosphate accumulation. Maximal stimulation of cAMP accumulation occurred with 1 x 10(-8) M of either peptide. These effects upon cAMP accumulation were competitively inhibited by the PTH antagonist, [Nle8, Nle18, Tyr34]bPTH(3-34)amide. Maximal stimulation of fibroblast inositol phosphates was reached at 1 x 10(-7) M of either peptide. In contrast, PTH and PTHrP at these concentrations produced no changes in cAMP or inositol phosphate metabolism in isolated type II pneumocytes. When pneumocytes were exposed to PTH or PTHrP and pulse-labelled with [methyl-3H]choline chloride, no hormone-stimulated changes in saturated phosphatidylcholine (PC) synthesis were detected. However, PTH and PTHrP stimulated saturated PC synthesis in rat fetal lung explants (gestational day 19-20) by 46% and 106%, respectively. When fibroblasts and pneumocytes were co-cultured, PTH and PTHrP again stimulated saturated PC synthesis by 45% and 73%, respectively. Taken together, these findings suggest that PTH and PTHrP may be endocrine and/or paracrine regulators of fetal lung development.

Effect of parathyroid hormone and calcitonin on acetylcholine release in rat sympathetic superior cervical ganglion

The effects of parathyroid hormone (PTH) and calcitonin on acetylcholine release by rat superior cervical ganglion (SCG) were evaluated in vitro. SCG labeled with [3H]choline were exposed to four 5 min-long pulses of 40 mM K+, 35 min apart. PTH increased, and calcitonin inhibited, in a dose-dependent way, K(+)-elicited [3H]acetylcholine release, with apparent effective doses 50 of about 10(-9) M. The effect of PTH was inhibited by co-incubation with the PTH receptor antagonist NLe [8-18]-PTH (3-34) amide. Incubation of SCG for 120 min with PTH or calcitonin resulted in dose-dependent augmentation or inhibition of K(+)-induced increase of high affinity [3H]choline uptake, respectively, with a maximal effect at 10(-8) M concentration (PTH) and 10(-9) M concentration (calcitonin) and declining at higher concentrations. The increase in SCG [3H]choline uptake induced by PTH was blunted by preincubation with the PTH antagonist NLe [8-18]-PTH (3-34) amide. At 10(-7) M concentrations, PTH increased significantly the in vitro conversion of [3H]choline to [3H]acetylcholine, an effect inhibited by PTH receptor antagonist. Calcitonin did not modify SCG [3H]acetylcholine synthesis by rat SCG. The results indicate that, in vitro, PTH increases, and calcitonin inhibits, acetylcholine release in rat SCG.

Structure and protein kinase C stimulating activities of lactam analogues of human parathyroid hormone fragment

Five analogues of human parathyroid hormone (hPTH-(20-34)-NH2, I; cyclo[Lys26-Asp30]-hPTH-(20-34)-NH2, II; cyclo[Glu22-Lys26]-hPTH-(20-34)-NH2, III; cyclo[Lys27-Asp30]- hPTH-(20-34)-NH2, IV; and [Leu27]-hPTH-(20-34)-NH2 V) were tested for their ability to promote membrane-bound protein kinase C (PKC) activity in a rat osteosarcoma cell line (ROS 17/2). Analogues I, II and V stimulated PKC activity in the picomolar range, whereas analogues III and IV did not stimulate this activity at any concentration tested. The circular dichroism spectra in neutral, aqueous buffer showed an increase in alpha-helix in analogues II, III and V as compared to I; this increase appeared to be in the region of the cyclic lactam structure. Analogue IV did not adopt a helical structure, even in the presence of 40% trifluoroethanol, a helix-promoting solvent. The remaining analogues showed a three- to four-fold enhancement of alpha-helix in this solvent. Analogues II and III had increased retention times in reversed-phase chromatography, as compared to I and IV. This is consistent with a stabilization of amphiphilic helix in analogues II and III compared with I and IV. The data suggest that in the region bounded approximately by residues 24-32, an amphiphilic alpha-helix is important for correct functional binding to the PTH receptor.

Further definition of the protein kinase C activation domain of the parathyroid hormone

The protein kinase C (PKC) activation domain of the parathyroid hormone (PTH) was believed to be the 28-34 region of the molecule. We have now shown that PTH-(29-32) is the smallest PTH fragment that can stimulate significantly membrane-associated PKC activity in ROS 17/2 rat osteosarcoma cells. As was previously shown for full-length PTH-(1-84) and the fully bioactive PTH-(1-34) fragment, there were two peaks in the PKC response to PTH-(29-32): one peak was obtained with low picomolar concentrations and the other with much higher nanomolar concentrations of the fragment. The PKC-activating ability was unaffected by the loss of Asn33 and Phe34, but it was abolished by removing His32. Thus, the PTH-(28-31) and PTH-(29-31) fragments did not stimulate membrane-associated PKC activity. The much larger PTH-(1-31) fragment also did not stimulate membrane-associated PKC activity, although it stimulated adenylyl cyclase as strongly as PTH-(1-34). This functional sensitivity to the loss of the polar His32 was not caused by a specific need for His or another polar amino acid in this position because replacing it with the apolar Leu did not abolish adenylyl cyclase or PKC activation. It is concluded that the minimum, fully functional PKC activation domain of the PTH molecule is Gln29-Asp30-Val31-His32.

C-terminal fragments of parathyroid hormone-related protein, PTHrP-(107-111) and (107-139), and the N-terminal PTHrP-(1-40) fragment stimulate membrane-associated protein kinase C activity in rat spleen lymphocytes

Membrane-associated protein kinase C (PKC) activity in lymphocytes freshly isolated from rat spleen was stimulated by the C-terminal parathyroid hormone-related protein fragments, PTHrP-(107-111) and PTHrP-(107-139), at concentrations from 10(-3) to 10(4) pM. By contrast, the same concentrations of PTHrP-(120-139), without the 107-111 TRSAW (-Thr-Arg-Ser-Ala-Trp-) sequence of the other C terminal fragments, did not stimulate spleen lymphocyte PKC. Low concentrations of the N-terminal PTHrP-(1-40) fragment also stimulated membrane-associated PKC activity in the spleen lymphocytes. These results suggest that PTHrP might be an important physiological regulator of the immune response.

Protein kinase C-activating domains of parathyroid hormone-related protein

N-terminal fragments of PTH-related protein (PTHrP), PTHrP-(1-34), and PTHrP-(1-40) stimulated both adenylyl cyclase and a mechanism that increases membrane-associated protein kinase C (PKC) activity in ROS 17/2 rat osteosarcoma cells. There were two peaks in the PKC response to the N-terminal PTHrP fragments: one peak was obtained with picomolar and the other with nanomolar PTHrP concentrations. The PKC-stimulating picomolar concentrations of the PTHrP fragments did not detectably stimulate adenylyl cyclase, but the nanomolar concentrations did. Since a similar two-peak response of PKC activity was obtained with PTHrP-(28-34), the single, N-terminal PKC activation domain of the PTHrP is in the same 28-34 region of the molecule as that of PTH despite this region having different primary amino acid sequences in the two hormones. Unlike PTH, PTHrP has a second PKC activation domain, as indicated by the ability of picomolar concentrations of the PTHrP-(107-111) fragment to stimulate maximally membrane-associated PKC activity in the osteosarcoma cells.

Apical and basolateral Na/H exchange in cultured murine proximal tubule cells (MCT): effect of parathyroid hormone (PTH)

Kidney proximal tubule Na/H exchange is inhibited by PTH. To analyze further the cellular mechanisms involved in this regulation we have used MCT cells (a culture of SV-40 immortalized mouse cortical tubule cells) grown on permeant filter supports. Na/H exchange was measured using single cell fluorescence microscopy (BCECF) and phosphate transport (measured for comparisons) by tracer techniques. MCT cells express apical and basolateral Na/H exchangers which respond differently to inhibition by ethylisopropylamiloride and by dimethylamiloride, the basolateral membrane transporter being more sensitive. Apical membrane Na/H exchange was inhibited by PTH (10(-8) M; by an average of 25%); similar degrees of inhibition were observed when cells were exposed either to forskolin, 8-bromo-cAMP or phorbol ester. Basolateral membrane Na/H exchange was stimulated either by incubation with PTH (to 129% above control levels) or by addition of phorbol ester (to 120% above control levels); it was inhibited after exposure to either forskolin or 8-bromo-cAMP. The above effects of PTH and phorbol ester (apical and basolateral) were prevented by preincubation of cells with protein kinase C antagonists, staurosporine and calphostin C; both compounds did not affect forskolin or 8-bromo-cAMP induced effects. PTH also inhibited apical Na-dependent phosphate influx (29% inhibition at 10(-8) M); it had no effect on basolateral phosphate fluxes (Na-dependent and Na-independent). Incubation with PTH (10(-8) M) resulted in a rapid and transient increase in [Ca2+]i (measured with the fluorescent indicator, fura-2), due to stimulation of a Ca2+ release from intracellular stores. Exposure of MCT cells to PTH did not elevate cellular levels of cAMP. Taken together, these results suggest that PTH utilizes in MCT cells the phospholipase C/protein kinase C pathway to differently control Na/H exchangers (apical vs. basolateral) and to inhibit apical Na/Pi cotransport.