Cytokine regulation of adult human osteoblast-like cell prostaglandin biosynthesis

Prostaglandin (PG) biosynthesis by cytokine stimulated normal adult human osteoblast-like (hOB) cells was evaluated by thin layer chromatography, high performance liquid chromatography, and specific immunoassays. PGE2 was the predominant PG formed under all incubation conditions tested. Control samples produced measurable amounts of PGE2, and the measured level of this metabolite increased by 22-fold (from 7 to 152 ng/ml) following a 20 h treatment with the combination of TGF beta and tumor necrosis factor-alpha(TNF). The production of 6-keto-PGF1 alpha (the stable metabolite of prostacyclin) and of PGF2 alpha were each increased by about five-fold (from about 0.5 to 2.5 ng/ml) in samples treated with the cytokines. Thus, TGF beta and TNF exerted a regulation of hOB cell PG biosynthesis that was principally directed towards an increased PGE2 biosynthesis, with lesser effects on the production of other PG metabolites. COX-2 mRNA levels were increased within 2 h of cytokine stimulation, reached a maximum at 6-12 h, and levels had appreciably diminished by 24 h after treatment. Both TGF beta and TNF could independently increase COX-2 mRNA levels and PG biosynthesis. However, the increased production of PGE2 resulting from TNF stimulation was blocked by the addition of an interleukin-1 beta (IL-1 beta) neutralizing antibody, suggesting that TNF regulation of hOB cell PG synthesis was secondary to its capacity to increase hOB cell IL-1 beta production. TGF beta regulation of PG production was not affected by the addition of the neutralizing antibody. These studies support the proposition that PGs can be important autocrine/paracrine mediators of bone biology, whose production by hOB cells is responsively regulated by osteotropic cytokines.

Regulation of collagenase-3 by bone morphogenetic protein-2 in bone cell cultures

Bone morphogenetic protein-2 (BMP-2), a member of the transforming growth factor superfamily of peptides, induces ectopic bone formation in vivo. The actions of BMP-2 on osteoblastic cells include stimulation of collagen synthesis, but the role of BMP-2 on collagen degradation is not known. We examined whether BMP-2 affects the expression of collagenase-3, an enzyme that degrades type I collagen at neutral pH, and that of tissue inhibitors of matrix metalloproteinases (TIMPs) in primary osteoblast-enriched cells from 22-day-old fetal rat calvariae. BMP-2 suppressed collagenase messenger RNA (mRNA) and immunoreactive protein levels. BMP-2 did not affect collagenase mRNA stability, but it reduced collagenase heterogeneous nuclear RNA levels and decreased the rate of transcription of the collagenase gene. BMP-2 also stimulated TIMP 1 and TIMP 3 mRNA levels, but failed to alter TIMP 2 expression. In conclusion, our studies indicate that BMP-2 suppresses collagenase-3 gene transcription and stimulates TIMP 1 and TIMP 3 expression in osteoblasts. The regulation of collagenase and TIMPs by BMP-2 in osteoblasts may play a role in osteoinduction.

Transforming growth factor beta1 inhibits collagenase 3 expression by transcriptional and post-transcriptional mechanisms in osteoblast cultures

Transforming growth factor (TGF) beta1 is an autocrine regulator of bone cell function. We demonstrated that TGF beta1 enhances bone collagen synthesis, but its effects on collagen degradation are not well characterized. We tested the effects of TGF beta1 on rat collagenase 3 expression in cultures of osteoblast-enriched cells from fetal rat calvariae (Ob cells). Treatment with TGF beta1 at 0.4 nM decreased steady state collagenase mRNA levels after 2 to 24 h. This dose-dependent effect was observed at TGF beta1 concentrations of 4 pM to 1.2 nM, and was accompanied by decreased levels of immunoreactive procollagenase. The protein synthesis inhibitor cycloheximide increased collagenase transcripts, but did not prevent the effect of TGF beta1 on collagenase mRNA levels. TGF beta1 accelerated the decay of collagenase mRNA in transcriptionally arrested Ob cells. In addition, TGF beta1 decreased the levels of collagenase heterogeneous nuclear RNA and the rate of collagenase gene transcription in Ob cells. TGF beta1 enhanced the expression of tissue inhibitors of metalloproteinases (TIMP) 1 and 3 and caused a modest decrease of TIMP 2 mRNA levels. In conclusion, TGF beta1 decreases interstitial collagenase transcripts and protease levels in Ob cells by transcriptional and post-transcriptional mechanisms, and this effect may contribute to its actions on bone matrix.

Transcriptional and posttranscriptional regulation of interstitial collagenase by platelet-derived growth factor BB in bone cell cultures

Platelet-derived growth factor (PDGF), a bone cell mitogen, stimulates bone collagen degradation and does not enhance bone matrix apposition rates. The mechanism of the effect on collagen degradation is unknown, and it could involve changes in interstitial collagenase synthesis. We tested the effects of PDGF on interstitial collagenase expression in cultures of osteoblast-enriched cells from fetal rat calvariae (Ob cells). After 4-8 h of treatment, PDGF BB at 0.3 nM increased steady state collagenase messenger RNA (mRNA), whereas PDGF AA had no effect. The effect of PDGF BB on collagenase transcripts was dose dependent. PDGF BB increased the levels of immunoreactive collagenase after 6 h, whereas the levels were decreased after 16 h. Stimulation of collagenase mRNA by PDGF BB was dependent on de novo protein synthesis and activation of protein kinase C. PDGF BB prolonged the half-life of collagenase mRNA in transcriptionally arrested cells. PDGF BB initially increased and subsequently decreased the rate of collagenase gene transcription and the levels of collagenase heterogeneous nuclear RNA. In conclusion, PDGF BB regulates interstitial collagenase in Ob cells by transcriptional and posttranscriptional mechanisms, and this effect may contribute to its stimulatory actions on bone collagen degradation.

Pemphigus herpetiformis

A 70-year old Indian lady with a two year history of a blistering eruption is described. This eruption clinically resembled dermatitis herepetiformis and responded to dapsone, however, histological and immunological investigations showed features of pemphigus herepetiformis.

Basic fibroblast growth factor stimulates expression of interstitial collagenase and inhibitors of metalloproteinases in rat bone cells

Basic fibroblast growth factor (bFGF) is a bone cell mitogen that affects osteoblastic function by suppressing type I collagen synthesis. The investigators in this study examined whether bFGF also regulates interstitial collagenase and tissue inhibitors of metalloproteinases (TIMPs) in osteoblast-enriched cells isolated from 22-day fetal rat calvariae. After exposure to 600 pM bFGF, interstitial collagenase messenger RNA (mRNA) levels, as determined by Northern hybridization analysis, increased after 2 h and were maximally stimulated to approximately 13-fold at 6 h. Exposure of osteoblast-enriched cells to 0.06-6 nM bFGF increased collagenase mRNA in a dose-dependent manner, and bFGF also increased immunoreactive collagenase measured in the culture medium by Western blot analysis. The protein synthesis inhibitor cycloheximide, as well as two inhibitors of protein kinase C, staurosporine and sangivamycin, prevented the bFGF induction of collagenase transcripts, whereas indomethacin, an inhibitor of prostaglandin synthesis, decreased the effect of bFGF on collagenase mRNA levels by about 50%. After exposure to 600 pM bFGF, levels of TIMP 1 and TIMP 3 mRNAs were also maximally stimulated to approximately 6-fold at 16 h and 4-fold at 6 h. bFGF did not modify TIMP 2 expression. In conclusion, bFGF may modulate degradation of collagenous bone matrix by inhibiting collagen as well as stimulating collagenase and TIMPs by osteoblasts.

Insulin-like growth factors inhibit interstitial collagenase synthesis in bone cell cultures

Insulin-like growth factor-I (IGF-I) and IGF-II are among the most prevalent growth factors secreted by bone cells and are presumed to act as autocrine regulators of bone formation. We recently demonstrated that IGFs inhibit bone collagen degradation, and we postulated that they may either inhibit the expression of interstitial collagenase or stimulate the synthesis of tissue inhibitors of metalloproteinase-1 (TIMP-1), -2, or -3. We tested the effects of IGF-I and -II on collagenase and TIMP-1, -2, and -3 expression in cultures of osteoblast-enriched cells from 22-day-old fetal rat calvariae (Ob cells). Steady state messenger RNA (mRNA) levels were determined by Northern blot analysis, and collagenase concentrations were determined in the culture medium by a specific immunoassay. After 2-6 h of treatment, IGF-I and -II decreased collagenase transcripts by up to 80%. IGF-I was a more potent inhibitor than IGF-II, because it was active at doses as low as 10 nM, whereas a dose of 100 nM was required to observe the IGF-II effect. In addition, IGF-I and -II opposed the stimulatory effect of retinoic acid on collagenase transcripts. Immunoreactive collagenase levels were not detectable in control or IGF-treated cultures, but IGF-I and -II decreased the levels induced by retinoic acid by 70-90%. The protein synthesis inhibitor cycloheximide superinduced collagenase transcripts, and IGF-I or -II decreased this mRNA induction to levels similar to, but not lower than, those observed in control cultures. The effects of IGF-I and -II on collagenase transcripts were not modified by the DNA synthesis inhibitor hydroxyurea at 1 mM. Neither IGF-I nor IGF-II modified the expression of TIMP-1, -2, or -3 mRNA in Ob cells. TIMP protein levels were not determined, and our study does not exclude a translational or posttranslational effect of IGF. In conclusion, IGF-I and -II decrease interstitial collagenase transcripts as well as induced protease levels in Ob cells, and this effect may contribute to their inhibitory actions on bone collagen degradation.

Transformation of human epidermal keratinocytes with fission neutrons

The biological effects of exposures to high LET radiations have particular relevance to radiation protection and risk assessment. Since most cancers are of epithelial origin, it is important to obtain a better understanding of radiation-induced oncogenic transformation in this cell type. Accordingly we have initiated studies to determine whether immortalized human epidermal keratinocytes (RHEK) can be transformed with high LET radiations. Exponentially growing RHEK cells were treated with single doses (1, 10, 25, 50 and 100 cGy) of 0.85 MeV fission neutrons from the Janus reactor. Neutron exposure led to the development of morphologically altered cells and foci formation after 6 weeks at confluence. These transformed cultures grew with an increased saturation density, exhibited anchorage-independent growth and formed tumors in athymic mice. Single-strand conformational polymorphism analysis and DNA sequencing demonstrated the absence of point mutations in codons 12/13 and 61 in the Ha-ras, Ki-ras, or N-ras genes and exons 4-9 of the p53 tumor suppressor gene. These studies demonstrate that high LET radiations (fission neutrons) can transform immortalized human epithelial cells to a malignant phenotype that does not appear to involve mutations in either the cellular p53 or ras genes.

Infant crying patterns in Manali and London

This study sought to assess the generalizability of the crying 'peak' previously found in Western infants at around 6 weeks of age. To this end, maternal reports and audiorecordings were used to compare the crying patterns of 2, 6 and 12-week-old infants in two cultures expected to differ in their approaches to babycare. As anticipated, Manali mothers were less inclined to leave their babies to cry, took them into their own beds more often, were more likely to be breastfeeding and breastfed their babies to an older age. In spite of these differences, both Manali and London mothers reported their babies to have an evening crying peak, most pronounced at 6 weeks, during this age-range; indicating that this is a general feature of infant development rather than a reflection of Western methods of babycare. Although the maternal reports suggested lower incidences of crying in the Manali infants, the study failed to produce convergent, tape-recorded evidence that this was the case. The definitional and methodological implications of the findings are discussed.

Regulation of interstitial collagenase expression and collagen degradation by retinoic acid in bone cells

In osteoblasts, retinoic acid (RA) modulates the synthesis of various proteins, including collagen. However, little is known about the effects of RA on the regulation of interstitial collagenase synthesis and collagen degradation. After treatment of primary osteoblast-enriched (Ob) cells from fetal rat calvariae with 100 nM all-trans-RA (tRA), collagenase mRNA levels, as determined by Northern blotting, did not change after 2 h, increased by 13- to 18-fold after 6 h, and remained elevated until 48 h. Exposure of Ob cells to 10 nM to 1 microM tRA, 13-cis-RA, and 9-cis-RA induced collagenase mRNA in a dose-dependent manner. Collagenase mRNA induction by RA was blocked by cycloheximide. RA increased the stability of collagenase mRNA in Ob cells, suggesting posttranscriptional regulation. Exposure of Ob cells to RA induced immunoreactive procollagenase in medium, as determined by enzyme-linked immunosorbent assay and Western blotting. RA action on collagen degradation was examined in [3H]proline-pulsed intact calvariae chased with and without tRA for 72 h. The release of [3H]hydroxyproline into culture medium was increased by 64% in the presence of 10 nM to 1 microM tRA. In conclusion, RA increases collagenase synthesis and collagen degradation in bone and is likely to play an important role in bone remodeling.

Growth factors regulate the synthesis of insulin-like growth factor-I in bone cell cultures

Insulin-like growth factor-I (IGF-I), a prevalent growth factor secreted by bone cells, has important effects on bone remodeling. Hormones are known to regulate the synthesis of skeletal IGF-I, but there is limited information about the actions of growth factors on IGF-I synthesis. We tested the effects of basic fibroblast growth factor (bFGF), transforming growth factor-beta 1 (TGF beta 1), and platelet-derived growth factors (PDGF) AA and BB on IGF-I mRNA expression and polypeptide concentrations in cultures of osteoblast-enriched (Ob) cells from 22-day-old fetal rat calvariae. Steady state IGF-I mRNA levels were determined by Northern blot analysis, and IGF-I concentrations were determined in acidified and fractionated culture medium by a specific RIA. Treatment of Ob cells with bFGF at 0.06-6 nM, TGF beta 1 at 0.04-4 nM, and PDGF BB at 0.3-3.3 nM caused a dose-dependent decrease in steady state IGF-I mRNA. A smaller effect was observed with PDGF AA. The effect was initially observed after 6-8 h of treatment and was maximal after 16 h. Treatment with bFGF at 0.6-6 nM, TGF beta 1 at 0.4-4 nM, and PDGF BB at 0.3-3.3 nM for 24 h decreased IGF-I polypeptide concentrations by 40-80%. The effects of bFGF, TGF beta 1, and PDGF BB and AA on IGF-I mRNA were independent of protein synthesis and cell division, as they were observed in the presence and absence of cycloheximide at 3.6 microM or hydroxyurea at 1 mM. Similarly, their inhibitory actions on immunoreactive IGF-I were not prevented by hydroxyurea. In conclusion, bFGF, TGF beta 1, PDGF BB, and, to a lesser extent, PDGF AA decrease skeletal IGF-I synthesis by reducing IGF-I transcript levels, and this effect may contribute to their actions on selected aspects of Ob cell function.

Role of platelet derived growth factor in bone cell function

PDGF is a mitogen for cells of the osteoblastic lineage. PDGF is present in the systemic circulation and is locally synthesized by skeletal cells. The systemic form primarily contains PDGF B chains, which are intrinsically more active than PDGF A subunits, the forms secreted by normal bone cells. PDGF AA is regulated by other growth factors and cytokines, which modulate its binding to osteoblastic receptors and its synthesis by skeletal cells. The exact role of PDGF in bone remodelling is still uncertain and current information suggests that this factor has a function in the response to inflammation and wound healing.

Rat thymosin beta 4 gene. Intron-containing gene and multiple retroposons

Thymosin beta 4 (T beta 4), a 43-residue peptide of uncertain function, is widely distributed in most tissues of vertebrates. Southern blot analysis demonstrated that the rat genome contains many closely related T beta 4 sequences. Two distinct T beta 4 sequences were isolated by screening a rat genomic DNA library. Analysis of these clones revealed that they represent T beta 4 retroposons; they lack introns and contain stretches of poly(A) sequence at their 3' ends and direct repeats flanking the cDNA-like sequences. In order to isolate a T beta 4 intron-containing gene, DNA fragments that include T beta 4 introns were generated by polymerase chain reaction, using rat genomic DNA as template. Subsequent Southern blot analysis of rat genomic DNA with intron-specific probes demonstrated the presence of a single T beta 4 intron-containing gene. Upon screening the rat genomic DNA library with an intron-specific probe, two overlapping clones of the T beta 4 intron-containing gene were isolated. Further characterization and sequence analysis showed that the rat T beta 4 intron-containing gene has a 2-kilobase pair-long transcription unit containing two introns. The transcription initiation site and putative regulatory elements of the promoter were identified.

Transcriptional regulation and chromosomal assignment of the mammalian calbindin-D28k gene

To determine whether 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] regulates transcription of the rat renal calbindin-D28k gene, the rate of calbindin-D28k mRNA synthesis was measured directly in nuclei using the in vitro nuclear transcription assay. Nuclei were prepared from kidneys of vitamin D-deficient rats at various times after a single ip injection of 1,25-(OH)2D3, and transcription was allowed to proceed in vitro in the presence of [32P]UTP for 30 min at 29 C, at which time the incorporation of UTP into trichloroacetic acid-precipitable material was optimal. Incorporation of UTP was decreased by 64.6% by alpha-amanitin, which selectively inhibits polymerase II. Purified [32P]RNA was analyzed for newly synthesized calbindin-D-28k gene transcripts by hybridization to calbindin-D28k cDNA immobilized on nitrocellulose filters. Using this assay we found that the first significant increase in calbindin-D28k gene transcription occurred at 1 h, and the peak of transcriptional activity occurred at 2 h. Within 12 h of 1,25-(OH)2D3 treatment, calbindin-D28k gene transcription returned to control levels. Using Northern blot analysis, a significant increase in calbindin-D RNA was first observed 2 h after hormone administration, reaching a maximum at 12 h. Renal calbindin-D28k protein levels are significantly increased by 3 h and reach a maximum value 48 h after hormone administration. Our results suggest that the early increase in renal calbindin-D28k may be due to transcriptional regulation. The long time lag between transcription and the peak of calbindin mRNA and calbindin protein accumulation may reflect the involvement of post-transcriptional mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular cloning of mammalian 28,000 Mr vitamin D-dependent calcium binding protein (calbindin-D28K): expression of calbindin-D28K RNAs in rodent brain and kidney

We report the isolation of a cloned cDNA for the mammalian 28,000 Mr vitamin D-dependent calcium binding protein (calbindin-D28K; CaBP28K) by immunological screening of a lambda gt11 bacterial expression library. The library contained cDNAs copied from poly(A)RNA of adult mouse cerebellum. We confirmed the identity of the CaBP28K cDNA by comparing its DNA sequence with that of chick CaBP28K cDNA. In the coding region, 79% of the mouse cDNA sequence was identical to the reported sequence of CaBP28K cDNA derived from chicken intestine. Rat brain and kidney each contain three species of poly(A)RNA that hybridize to CaBP28K cDNA--a major species of 1.9 kb, and rarer components of 2.8 kb and 3.2 kb. All three RNAs appear to be transcribed from a single gene. The ratios of these CaBP28K RNAs were the same in brain and kidney. In the cerebellum, in situ hybridization reveals that CaBP28K RNAs are confined to Purkinje neurons.

Analysis of rat vitamin D-dependent calbindin-D28k gene expression

We report the use of a cloned cDNA for mammalian calbindin-D28k (28-kDa vitamin D-dependent calcium-binding protein) to study the expression of the rat calbindin gene. Tissue distribution studies, using Northern analysis, indicated that calbindin-D28k-mRNA is detected in rat kidney and brain but is not detected in rat intestine, testes, bone, pancreas, liver, lung, or skeletal muscle. Both rat kidney and brain contain three RNA species (1.9, 2.8, and 3.2 kilobase pairs). The regulation of the gene was characterized by both Northern and slot blot analysis. Hormonal regulation, developmental expression of calbindin-D28k-mRNA, and the effect of dietary alteration were examined. In the kidney all three species of mRNA were dependent on the presence of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) for their induction. The time course of induction of renal calbindin-D28k-mRNA indicated that a significant increase in calbindin-D-mRNA was detectable as early as 2 h following a single injection of 1,25-(OH)2D3 (200 ng/100 g of body weight), reaching a maximum at 12 h. Unlike the kidney high levels of calbindin-D28k-mRNA were observed in the brain of vitamin D-deficient rats. The concentration of calbindin-D28k-mRNA in brain was unchanged after 1,25-(OH)2D3 administration. Developmental studies indicated that calbindin-D-mRNA in rat kidney and brain is present prior to birth but is developmentally regulated in a tissue-specific manner. The most pronounced changes in the abundance of renal calbindin-D28k-mRNA occur between birth and 1 week of age. Unlike the kidney a large increase in brain calbindin-D28k-mRNA occurs at a later time, between 1 and 2 weeks of age (the period of major synapse formation). In dietary alteration studies results of Northern blot analysis indicate that low dietary phosphorus results in increased calbindin-D-mRNA in kidney but not in brain. These studies represent the first analysis of the rat calbindin-D28k gene and its regulation in vivo. Our findings suggest that in rat kidney and brain there are significant differences both in the expression of the gene for calbindin-D28k and its regulation by 1,25-(OH)2D3.

A quantitative immunobinding assay for vitamin D-dependent calcium-binding protein (calbindin-D28k) using nitrocellulose filters

A sensitive dot immunobinding assay has been developed for the quantitative determination of vitamin D-dependent calcium-binding protein (calbindin-D28k; CaBP) in rat and human kidney and brain. Protein samples are spotted onto nitrocellulose sheets, fixed, and then rinsed with Tris-buffered saline. The remaining protein binding sites are blocked with bovine serum albumin, gelatin, or nonfat dry milk protein and the filters are then incubated sequentially with antiserum to calbindin-D28k (1:500 dilution) and 125I-protein A (200,000 cpm/ml). After washing, the radioactivity bound to each sample is quantitated by counting in a gamma counter. The sensitivity of the assay is such that 10 ng calbindin-D28k can be accurately quantitated. The highest levels of CaBP were detected in kidney (7.8 +/- 0.5 micrograms/mg protein) and cerebellum (22.1 +/- 1.4 micrograms/mg protein). Ten micrograms calmodulin, lactalbumin, or parvalbumin and 100 micrograms liver extract showed no reactivity in the assay. The assay is precise (intraassay variability, 4.0%) and reproducible (interassay variability, 8.8%). There was good agreement between the data in this assay and the data we obtained using radioimmunoassay (RIA). The assay has several advantages over the RIA. Iodination of pure antigen is not required and it is possible to detect membrane-bound and insoluble antigens using this assay. Also, the antiserum and 125I-protein A solutions can be saved and reused. This assay represents a major modification of the original immunobinding assays which used the less sensitive peroxidase stain. It is also an improvement over previous 125I immunobinding assays which were not quantitative but were used as antigen "spot tests" or which required iodination of the antibody.

Pars flaccida cholesteatoma as demonstrated by computed tomography

Prior to the availability of high-resolution computed tomography (CT), the mainstay of roentgenographic diagnosis of cholesteatoma was conventional filming and complex motion tomography. The precise extent of the soft-tissue mass was very difficult to delineate with these methods, and one relied on indirect findings such as bony erosion and displacement. With high-resolution CT, the soft-tissue mass itself can be seen. Typical modes of extention of pars flaccida cholesteatomas of varying size are illustrated in this study.

Lung lipoprotein lipase: inhibition by barbiturates

The action of barbiturates on the enzymatic activity of lung lipoprotein lipase has been studied in vitro and in vivo. Mouse lung preparations can be separated into two fractions containing lipoprotein lipase activity and designated as soluble and membrane-bound. In vitro, both enzyme fractions were inhibited in a graded manner by the barbiturates when present in concentrations of 1-4 mg/ml. Experiments to determine the mechanism for the inhibition of lipoprotein lipase suggest that it may be related to non-specific binding of the drug to the enzyme since other drugs e.g., phenylbutazone and a coumarin derivative which bind non-specifically to serum albumin showed similar inhibitory activity. When rat lungs were perfused in situ with heparin, 49% of the total lipoprotein lipase activity was released into the perfusate. However, when pentobarbital was perfused prior to heparin, no lipoprotein lipase activity was observed in the perfusate. The possible clinical implications resulting from inhibition of pulmonary lipoprotein lipase by barbiturates are discussed in this paper.

Modulation of the activity of the (Ca2+ + Mg2+)-dependent adenosine triphosphatase of the human erythrocyte

We previously reported that the activity of the (Ca2+ + Mg2+)-dependent adenosine triphosphatase (ATPase) of the human erythrocyte membrane is inhibited by micromolar or nanomolar concentrations of cyclic AMP. Our further studies have now indicated that the inhibition of (Ca2+ + Mg2+)-dependent phosphohydrolase activity requires the participation of a membrane-associated cyclic AMP-dependent protein kinase and a membrane-associated protein substrate that is distinct from the ATPase itself. We have furthermore, identified a 20 kDa membrane protein which undergoes phosphorylation that is promoted by micromolar, but not millimolar, concentrations of cyclic AMP and which, when phosphorylated, undergoes dephosphorylation that is promoted by Ca2+. We suggest that this membrane component can participate in the modulation of the activity of the (Ca2+ + Mg2+)-dependent ATPase of the human erythrocyte.

The influence of adenosine 3',5'-monophosphate upon the activity of the membrane-associated (Ca+ + Mg2+)-dependent adenosine triphosphatase of the human erythrocyte

The phosphohydrolase activity of the membrane-associated (Ca2+ + Mg2+)-dependent adenosine triphosphatase (ATPase) of the human erythrocyte can be inhibited by micromolar of nanomolar concentrations of cyclic AMP. Millimolar concentrations of cyclic AMP are less effective. The inhibitory effect of cyclic AMP is potentiated in the presence of the phosphodiesterase inhibitor, theophylline.

Orbital malignant non-chromaffin paraganglioma. Alveolar soft tissue sarcoma

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