Search PubMed⌕ Search

Biomedical subjects

P Esbrit

Publications and source records attributed to P Esbrit.

At least 37 records · Page 2Linked to original sources
PubMed1999

Effects of transforming growth factor beta1 on cell growth and parathyroid hormone-related protein in Walker 256 tumor cells.

Hypercalcemic strains of the rat Walker 256 (W256) tumor synthesize parathyroid hormone-related protein (PTHrP) and at least one of them produces an ill-defined transforming growth factor activity. We tested the production of transforming growth factor (TGF) beta by a hypercalcemic W256 tumor strain, and assessed its effects on tumor cell growth and PTHrP expression. We found that addition of TGF beta1 for 7 days inhibited cell growth ([3H]thymidine incorporation and cell number) dose dependently, between 0.04-20 pM. The antiproliferative effect of TGF beta1 on W256 tumor cell growth was likely mediated by binding to high affinity receptors (Kd = 14 pM) in these cells. At different tumor cell growth stages, acidified cell-conditioned medium contained immunoreactive TGF beta1. However, the nonacidified tumor cell-conditioned medium was found to contain neither immunoreactive nor bioactive TGF beta. Moreover, exposure of W256 tumor cells to a neutralizing anti-TGF beta1 antibody failed to affect tumor cell proliferation. Thus, W256 tumor cells appear to secrete TGF beta in an inactive form. Using reverse transcription followed by PCR, we found that addition of 20 pM TGF beta1 increased its own mRNA expression, apparently by stimulating gene transcription, within 6-12 h in W256 tumor cells. In addition, 20 pM TGF beta1 stimulated PTHrP mRNA in these cells at 24 h; an effect which was mediated, at least in part, by increasing PTHrP mRNA stability. Immunoreactive PTHrP decreased in the W256 tumor cell-conditioned medium after treatment with 20 pM TGF beta1 for 24-48 h. These results support the validity of this W256 tumor strain for in vivo studies to clarify the relative role of TGF beta and PTHrP in the pathogenesis of humoral hypercalcemia of malignancy.

Animals↗
PubMed1999

Influence of skeletal site of origin and donor age on 1,25(OH)2D3-induced response of various osteoblastic markers in human osteoblastic cells.

Age-related bone loss may be a consequence of a lack of osteoblastic formation and/or function. In vitro, the osteoblastic response to 1,25(OH)2D3, an important regulator of osteoblastic function, appears to depend on the stage of osteoblastic maturation. In this study, we examined the response to 1,25(OH)2D3 of C-terminal type I procollagen (PICP), alkaline phosphatase (ALP), and osteocalcin (OC) secretion in primary cultures of osteoblastic cells from human trabecular bone (hOB). Forty-four bone samples were obtained from subjects undergoing knee arthroplastia, 20 aged 50-70 (64 +/- 5), and 24 >70 (73 +/- 2) years. Another 33 bone samples were obtained from subjects undergoing hip arthroplastia, 21 were aged 50-70 (64 +/- 4) and 12 >70 (75 +/- 5) years. Pooling knee and hip hOB cell cultures, we found that PICP secretion decreased after 1,25(OH)2D3 in hOB cells from the older group (>70 years). Treatment with 1,25(OH)2D3 increased ALP secretion in these cells only in the younger group (50-70 years), whereas it increased OC secretion in hOB cells in both age groups. By pooling hOB cell cultures from both age groups we found that knee hOB cells increased OC secretion, and decreased PICP secretion, after 1,25(OH)2D3. This metabolite also increased OC secretion in hip hOB cells. Considering the influence of donor age at the same skeletal site, 1,25(OH)2D3 was found to stimulate ALP secretion only in knee hOB cells in the younger group. In contrast, this metabolite decreased ALP secretion in hip hOB cells in the older group. PICP secretion decreased after 1,25(OH)2D3 only in hOB cells in the older group, at both skeletal sites. In age-matched cultures, OC secretion was lower in hip hOB cells compared with those from the knee in the older group, but was similar in these cell cultures from both skeletal sites in the younger group. OC secretion after 1,25(OH)2D3 stimulation did not show age differences in knee hOB cells, but was lower in hip hOB in the older group. In summary, our results demonstrate that the response of various osteoblastic markers to 1,25(OH)2D3 in primary cultures of hOB cells depends on the donor age and skeletal site of origin.

Aged↗
PubMed1999

Renal expression of parathyroid hormone-related protein (PTHrP) and PTH/PTHrP receptor in a rat model of tubulointerstitial damage.

BACKGROUND: PTHrP, which appears to act as a growth/differentiation factor in a variety of tissues, is present in the kidney; however, its role is unclear. METHODS: The expression of PTHrP and the PTH/PTHrP receptor were investigated by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry in the remnant kidney of uninephrectomized (UNX) rats after protein overloading [1 g/day of bovine serum albumin (BSA)]. RESULTS: Compared with UNX-control rats, proteinuria in BSA-overloaded animals was detected within the first 24 hours and increased during the entire study period (28 days). Kidney examination by light microscopy showed no significant renal lesions at day 1 of BSA treatment, whereas at days 8 and 28, tubular lesions, infiltration of mononuclear cells, and mesangial expansion were observed. PTHrP mRNA expression in the renal cortex was already increased at day 1 (fourfold) and plateaued between days 8 and 28 (12- and 15-fold, respectively) in BSA-overloaded animals compared with UNX-control rats. At day 8, immunohistochemical analysis with two different anti-PTHrP antibodies showed a dramatic increase of PTHrP staining in the damaged proximal and distal tubules from BSA-overloaded rats with respect to UNX-control rats. Moreover, intense PTHrP immunostaining was also observed in glomerular mesangial and endothelial cells in BSA-overloaded rats, but not in the UNX-control rats. A reciprocal decrease of PTH/PTHrP receptor mRNA and immunostaining, without significant changes in the cellular localization (proximal and distal tubule, and glomerular mesangial and epithelial cells) of the PTH/PTHrP receptor positivity was found to occur in the renal cortex of BSA-overloaded rats. At day 8, coinciding with the up-regulation of PTHrP, an increase in the angiotensin converting enzyme and preproendothelin-1 gene expression was observed in the renal cortex of BSA-overloaded rats compared with UNX-control rats. CONCLUSIONS: These results indicate that PTHrP can be added to the group of genes that are up-regulated in proximal tubular cells in response to intense proteinuria. Our results, together with previous findings, suggest that the vasoactive hormones angiotensin II and endothelin-1 could participate in the PTHrP production in the renal cortex of BSA-overloaded rats. Further experiments are required to clarify the mechanisms of PTHrP up-regulation and its possible role in the response to renal damage in this animal model.

Animals↗
PubMed1999

Parathyroid hormone-related peptide stimulates DNA synthesis and insulin secretion in pancreatic islets.

Parathyroid hormone (PTH)-related protein (PTHrP) is present in the pancreatic islet. Recent data in transgenic mice suggest that PTHrP might modulate islet mass and insulin secretion. In the present study, we assessed the effect of the N-terminal PTH-like region of PTHrP on DNA synthesis in isolated rat islets. PTHrP (1-34), between 1 pM and 10 nM, for 48 h stimulated []thymidine incorporation into rat islets. This effect was maximally induced, about 2.5-fold over control, by 10 pM of this peptide, decreasing thereafter. In contrast, PTHrP (38-64) amide or PTHrP (107-139) were ineffective in increasing DNA synthesis in islets. Using reverse transcription followed by PCR, we confirmed that rat islets express PTHrP and the type I PTH/PTHrP receptor. Addition of a neutralizing anti-PTHrP antibody to the incubation medium of proliferating islets decreased islet DNA synthesis by 30%. The effect of a submaximal dose (30 pM) of PTHrP (1-34) on DNA synthesis in rat islets was abolished by 25 nM bisindolylmaleimide I, a protein kinase C (PKC) inhibitor, but not by 25 microM adenosine 3',5'-cyclic monophosphorothioate, Rp-isomer, a protein kinase A inhibitor. Moreover, 100 nM phorbol-12-myristate-13-acetate for 48 h also increased DNA synthesis 2-fold over controls in islets. PTHrP (1-34), at 100 nM, in contrast to 50 microM forskolin or 10 mM NaF, failed to affect adenylate cyclase activity in islet membranes. PTHrP, at 30 pM, was also found to increase 2-fold insulin released into the islet-conditioned medium within 24-48 h. Our results suggest that PTHrP is a modulator of pancreatic islet growth and/or function by a PKC-mediated mechanism.

Adenylyl Cyclases↗
PubMed1999

Parathyroid hormone-related protein (107-139) stimulates interleukin-6 expression in human osteoblastic cells.

The N-terminal region of both parathyroid hormone (PTH) and PTH-related protein (PTHrP) binds to the same PTH/PTHrP receptor in osteoblasts. However, C-terminal PTHrP (107-139) inhibits growth and various functions of osteoblasts and osteoclasts apparently through PTHrP-specific receptors. PTH (1-34) and PTHrP (1-34) rapidly induce interleukin-6 (IL-6) expression by osteoblasts. The aim of the present study was to assess the effects of PTHrP (107-139) on IL-6 gene expression and secretion by osteoblastic cells from human trabecular bone (hOB). Using reverse transcription followed by PCR, it was found that IL-6 mRNA was twofold maximally increased by either PTHrP (1-34) or PTHrP (107-139), at 10 nM, over basal within 1 to 2 h in hOB cells. This effect of PTHrP (107-139), and that of PTHrP (1-34), were abolished by the transcription inhibitor actinomycin D. Meanwhile, puromycin, a protein synthesis inhibitor, superinduced IL-6 expression in the presence or absence of each PTHrP peptide. Both PTHrP (1-34) and PTHrP (107-139), but not PTHrP (38-64), stimulated IL-6 secretion to the hOB cell-conditioned medium at 24 h, dose dependently. In addition, this maximal stimulatory effect (twofold over basal) was similar with each PTHrP peptide alone, and not additive when added together. PTHrP (107-139) stimulation of mRNA and protein in hOB cells was abolished by bisindolylmaleimide I, a protein kinase C inhibitor, but not by either adenosine 3',5'-cyclic monophosphorothioate, Rp-isomer (Rp-cAMPS), or N-[2-((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H89), two protein kinase A inhibitors. These results indicate that C-terminal PTHrP, like its N-terminal domain, induces IL-6 production by human osteoblastic cells. This effect of both PTHrP regions could provide a mechanism to modulate bone turnover.

Adult↗
PubMed1998

Cyclosporine increases renal parathyroid hormone-related protein expression in vivo in the rat.

BACKGROUND: Clinical use of cyclosporine (CsA) is limited by its known nephrotoxicity. Parathyroid hormone (PTH)-related protein (PTHrP) increases after acute renal ischemia and stimulates proliferation of renal cells in culture. Herein, we have examined whether the renal expression of PTHrP and its PTH/PTHrP receptor is affected by chronic CsA nephrotoxicity. METHODS: Rats were randomly assigned to receive daily intramuscular injections of either CsA (25 mg/kg) or the same volume of the vehicle olive oil (control) for 3 weeks. At this time interval, under ether anesthesia, rat blood and kidneys were obtained for analytical determinations, and total RNA isolation or immunohistochemistry, respectively. RESULTS: Serum urea was 11+/-2 and 6+/-1 mmol/L (P < 0.01) in CsA-treated and control rats, respectively. We found that PTH/PTHrP receptor mRNA was unchanged, but PTHrP mRNA, and also transforming growth factor-beta1 mRNA expression as positive control, was about twofold increased in the kidney of CsA-treated rats. This was accompanied by increased PTHrP immunostaining in renal cortical tubules, associated with tubule vacuolation. CONCLUSION: This study demonstrates an up-regulation of PTHrP, associated with chronic CsA-induced nephrotoxicity. Our findings support a role for PTHrP in the CsA-injured kidney.

Animals↗
PubMed1998

Comparison of two immunoradiometric assays for parathyroid hormone-related protein in the evaluation of cancer patients with and without hypercalcemia.

Hypercalcemia is a common paraneoplastic syndrome due to the secretion by tumors of parathyroid hormone-related protein (PTHrP) and/or other osteolytic factors. In the present study, we have measured plasma PTHrP using two immunoradiometric assays for PTHrP, assay N (Nichols) and assay I (INCSTAR), recognizing the 1-86 domain of PTHrP, for the evaluation of malignancy-associated hypercalcemia. The study included 25 tumor patients with hypercalcemia (HCa) [corrected serum calcium (SCa) > or = 2.70 mmol/L], 20 normocalcemic patients with cancer (NCa), and ten healthy control subjects. Plasma PTHrP was either undetectable or within the respective normal range in the majority of NCa patients and in the control subjects, with both assays. Plasma PTHrP was increased in 13 and 15 of HCa cases with assay N and assay I, respectively. PTHrP was elevated in plasma in 5/6 (assay N) and 3/6 (assay I) HCa patients with squamous tumors. However, plasma PTHrP was high in only 2/9 (assay N) and 1/9 (assay I) HCa cases with hematological tumors. Less than 40% of HCa patients with bone metastases, and >75% of those without bone involvement, had elevated plasma PTHrP with both assays. Detectable plasma PTHrP and SCa were significantly correlated using assay N (p = 0.025) and assay I (p = 0.01), in the HCa group. A highly significant correlation (p <0.001) was found between detectable plasma PTHrP with both assays, and a high agreement between them based on simple kappa statistics (p < 0.001), in the latter group. Our results indicate that each assay may be similarly useful in detecting PTHrP hyperproduction in cancer patients.

Adult↗
PubMed1998

Parathyroid hormone-related protein increases DNA synthesis in proximal tubule cells by cyclic AMP- and protein kinase C-dependent pathways.

The present study was performed to characterize the possible involvement of cAMP synthesis and protein kinase C (PKC) activation in the DNA synthesis-stimulating effect of parathyroid hormone-related protein (PTHrP) in proximal tubule cells. We found that DNA synthesis was stimulated by 10 microM 8BrcAMP, and 1 microM Sp-cDBIMPS, two cAMP analogs, and also by 1 microM phorbol 12-myristate 13-acetate (PMA) and 100 microM 1,2-dioctanoyl-sn-glycerol, two PKC activators, and 10 nM [Cys23] human (h)PTHrP (24-35) amide in rabbit proximal tubule cells (PTC). Both Sp-cDBIMPS and PMA, at 1 microM, also increased DNA synthesis in SV40-immortalized mouse proximal tubule cells MCT. Human PTHrP (7-34) amide [PTHrP (7-34)] dose dependently stimulated DNA synthesis in a similar manner as [34Tyr]PTHrP (1-34) amide [PTHrP (1-34)], in PTC. PMA pre-treatment for 20 h, which downregulates PKC, completely blocked the effect induced by PTHrP (7-34), but not that of PTHrP (1-34), in the latter cells. In contrast, the same PMA pre-treatment abolished the DNA synthesis stimulation by PTHrP (1-34) and PTHrP (7-34) in MCT cells, which appear to have PTH receptors mainly coupled to phospholipase C and not adenylate cyclase. Our results indicate that the stimulatory effect of PTHrP on DNA synthesis in proximal tubule cells is mediated by a cAMP- and PKC-dependent mechanism.

Adenylyl Cyclases↗
PubMed1997

Antiproliferative effect of the C-terminal fragments of parathyroid hormone-related protein, PTHrP-(107-111) and (107-139), on osteoblastic osteosarcoma cells.

The C-terminal region of parathyroid hormone-related protein (PTHrP) containing the sequence (107-111) appears to be a potent inhibitor of osteoclastic bone resorption. In the present study, we have investigated the effect of human (h)PTHrP (107-139) and hPTHrP (107-111)NH2 on the proliferation of osteoblastic rat osteosarcoma UMR 106 cells. We found that both C-terminal PTHrP peptides, like hPTHrP (1-141), were antimitogenic for these cells, between 1 pM and 10 nM. [Tyr34]hPTHrP (1-34)NH2 was as potent as these peptides but less effective as growth inhibitor in these cells. UMR 106 cells were found to produce and secrete immunoreactive PTHrP. Addition of anti-PTHrP neutralizing antibodies to C- and N-terminal epitopes of PTHrP increased the growth of these cells. Our data suggest that the antiproliferative effect of these C-terminal PTHrP analogs may be independent of cyclic adenosine 3':5'-monophosphate (cAMP) and mediated by protein kinase C. These findings support an autocrine role of PTHrP in bone metabolism.

Animals↗
PubMed1997

C-terminal parathyroid hormone-related protein inhibits proliferation and differentiation of human osteoblast-like cells.

Parathyroid hormone-related protein (PTHrP) is synthesized by osteoblasts, although its local role in bone is not completely understood. The C-terminal (107-111) region of PTHrP seems to be a potent inhibitor of osteoblastic bone resorption. We studied the effect of this PTHrP domain on the proliferation and synthesis of osteoblastic markers in osteoblast-like cells from adult human bone. We found that the human (h)PTHrP(107-139) fragment, between 10 fM and 10 nM, inhibited 3H-thymidine incorporation into these cells. The antiproliferative effect of the latter fragment, or that of hPTHrP(107-111), was similar to that induced by [Tyr34] hPTHrP(1-34) amide, bovine PTH(1-34), and hPTHrP(1-141), while hPTHrP(38-64) amide was ineffective. Human PTHrP(7-34) amide, at 10 nM, and 1 microM phorbol-12-myristate-13-acetate also significantly decreased DNA synthesis in human osteoblast-like cells. Neither hPTHrP(7-34) amide nor hPTHrP(107-139), at 10 nM, stimulated protein kinase A (PKA) activity in these cells. Moreover, 100 nM H-89, a PKA inhibitor, did not eliminate the inhibitory effect of hPTHrP(107-139) on these cells' growth. However 100 nM calphostin C, a PKC inhibitor, blunted this effect of PTHrP(107-139). In addition to their antimitogenic effect, hPTHrP(107-139) and hPTHrP(107-111) inhibited basal and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3)-stimulated alkaline phosphatase activity in these cells. Both fragments, like 1,25(OH)2D3, decreased C-terminal type I procollagen secretion into the cell-conditioned medium, but osteocalcin secretion by these cells was unaffected by the C-terminal PTHrP fragments. These findings suggest that PTHrP may act as a local regulator of bone formation.

Aged↗
PubMed1996

Comparison of antiproliferative effects of atrial natriuretic peptide and transforming growth factor beta on rabbit kidney proximal tubule cells.

The effects of atrial natriuretic peptide (ANP) and transforming growth factor beta (TGF beta) on cell proliferation were investigated in rabbit kidney proximal tubule cells. At 48 h, each agonist inhibited cell growth dose dependently. Moreover, the antiproliferative effect of both factors together was greater than that of each factor alone. However, coincubation of a high concentration (100 nM) of ANP and epidermal growth factor (EGF) was found to induce cell hypertrophy. This hypertrophic effect induced by ANP in the presence of EGF was mimicked by 8-BrcGMP but not by various cAMP analogues, at 100 microM, and was independent of the tyrosine kinase inhibitor genistein (10 microM). However, it was inhibited by 100 pM TGF beta. These in vitro results suggest that the antiproliferative effects of ANP and TGF beta may be part of a mechanism to modulate the hyperplastic effect of EGF in the renal proximal tubule during compensatory kidney growth.

Analysis of Variance↗
PubMed1996

Hypertrophy of rabbit proximal tubule cells is associated with overexpression of TGF beta.

The expression of transforming growth factor beta (TGF beta) in proximal tubule cells from rabbit kidney cortex after uninephrectomy (UNX) was investigated. Cell protein and [3H]leucine incorporation in these cells were significantly increased, while cell number was decreased, at two weeks following UNX. At this time period after UNX, we found that proximal tubule cells showed a dramatic increase of cytoplasmic immunostaining with a pan-specific anti-TGF beta antibody. This was accompanied by a 3-fold increase in TGF beta 1 mRNA expression in these cells. Furthermore, proximal tubule cells from two-week uninephrectomized rabbits secrete about 2-fold higher TGF beta bioactivity to the cell conditioned medium compared to cells from sham-operated animals. Addition of anti-TGF beta 1, beta 2, beta 3 neutralizing antibody increased the growth of the former cells, and it abolished cell hypertrophy. These results indicate that hypertrophy of proximal tubule cells during compensatory renal growth is associated with overexpression of TGF beta.

Animals↗
PubMed1996

Immunohistochemical detection of parathyroid hormone-related protein in a rare variant of hepatic neoplasm (sclerosing hepatic carcinoma).

Sclerosing hepatic carcinoma represents an uncommon subtype of hepatic malignancy, frequently associated with hypercalcemia. We applied immunohistochemistry using the avidin-biotin-complex technique to examine the presence of parathyroid hormone-related protein (PTHrP) in formalin-fixed and paraffin-embedded sections of tissue from a case of sclerosing hepatic carcinoma obtained at autopsy. Two polyclonal antibodies against the regions 24 to 35 and 107 to 111 of human PTHrP, and a monoclonal antibody that recognizes the human sequence 38 to 64 of this protein, were used. Preabsortion tests using the corresponding synthetic peptide as antigen were done with these antibodies. The neoplastic tissue displayed cytoplasmic immunostaining, diffuse with the antibodies against the amino- or carboxy-terminal regions of PTHrP, and with a predominant peripheral pattern when using the antibody to the midregion of the molecule. Tumor cells positive for PTHrP were also positive for hepatocellular markers cytokeratins 10, 17, and 18, but negative for chromogranin A. Our findings provide the first evidence for PTHrP production in the sclerosing subtype of hepatic carcinoma.

Antibodies, Monoclonal↗
PubMed1995

Parathyroid hormone-related protein is an autocrine modulator of rabbit proximal tubule cell growth.

Parathyroid hormone-related protein (PTHrP), a likely mediator for humoral hypercalcemia of malignancy, is also synthesized in various normal tissues. In the kidney, PTHrP, mainly detected in proximal and distal tubules, has been shown to stimulate proliferation of rat mesangial cells in culture. Experiments were carried out to investigate the possible mitogenic effect of PTHrP in cultures of rabbit proximal tubule cells (PTC). Immunocytochemical analysis, using antihuman (h)PTHrP antibodies to (38-64) and (107-111) epitopes in the PTHrP molecule, showed strong cytoplasmic staining in PTC and proximal tubule-like LLC-PK1 cells. PTC secreted immunoreactive PTHrP (54.8 +/- 7.0 fmol/10(6) cells) into the culture medium. Human PTHrP(1-141) stimulated proliferation in subconfluent cultures of these cells dose-dependently. This effect was similar to that induced by [Tyr34]hPTHrP(1-34) amide (hPTHrP[1-34]), hPTHrP(1-86), and bovine (b)PTH(1-34), while hPTHrP(38-64) amide, hPTHrP9107-111) amide, and hPTHrP(107-139) amide were ineffective. Addition of anti-hPTHrP neutralizing antibodies to (1-34), (38-64), and (107-111) epitopes of PTHrP decreased PTC growth. The mitogenic effect of these agonists was abolished in confluent PTC. In contrast, [Nle8,18, Tyr34]bPTH(3-34)amide (bPTH[3-34]) increased DNA synthesis in either subconfluent or confluent PTC. In LLC-PK1 cells, which also secreted PTHrP and are devoid of PTH receptors, none of these peptides affected proliferation. Forskolin (10 microM) or H-8 (2 microM), a protein kinase A inhibitor, did not affect basal or hPTHrP(1-34)-stimulated DNA synthesis, respectively, in subconfluent PTC. On the other hand, 10 nM staurosporine and 100 nM calphostin C, protein kinase C (PKC) inhibitors, blunted the effects of hPTHrP(1-34) or bPTH(3-34) on DNA synthesis in these cells. These studies suggest that PTHrP may function as an autocrine factor in the regulation of proximal tubule cell growth by a PKC-mediated mechanism.

Alkaloids↗
PubMed1994

Proliferative effect of parathyroid hormone-related protein on the hypercalcemic Walker 256 carcinoma cell line.

The rat Walker 256 carcinoma is an animal model for humoral hypercalcemia of malignancy. This tumor produces and secretes parathyroid hormone (PTH)-related protein (PTHrP), a likely mediator for this syndrome. In this study, we investigated the effect of PTHrP on Walker 256 tumor cell proliferation. We found that [Tyr36]human (h)PTHrP (1-36)NH2 and hPTHrP (1-86), unlike hPTHrP (38-64)NH2, stimulate DNA synthesis dose-dependently in these cells. A similar mitogenic effect was also observed with bovine (b)PTH (1-34) or (Nle8.18, Tyr34)bPTH (3-34)NH2. Moreover, addition of anti-hPTHrP (1-34) neutralizing antibodies decreased tumor cell growth. Conversely, 10(-4)M dibutyryl cAMP or Sp-cDBIMPS (a cAMP analogue) inhibited DNA synthesis in these cells, being incompetent at lower doses. PTHrP or PTH failed to stimulate cAMP production, but they induced a cytosolic calcium transient increase in these cells. These findings support an autocrine role of PTHrP in the regulation of this tumor growth.

1-Methyl-3-isobutylxanthine↗
PubMed1993

Characterization of calcium transport in the luminal and the basolateral membrane from kidney cortex of hypercalcemic rats bearing the Walker 256 carcinosarcoma.

The Walker 256 (W256) carcinosarcoma did not significantly modify calcium uptake by brush border membrane (BBM) vesicles in the kidney of the host rat, compared with that in membranes isolated from control animals. However, it showed a tendency to increase at near equilibrium in W256 tumor-host rats, associated with a decreased BBM protein content. ATP-dependent calcium influx by basolateral membrane (BLM) vesicles from W256 tumor-bearing rats was also increased compared with that in control BLM. This stimulation was due to a decreased Km for calcium. Passive calcium permeability or the Na+/Ca2+ exchanger were unchanged in BLM from W256 tumor-host rats compared with control BLM. Pre-stimulation of control rat cortical tubules with either 10(-7) M parathyroid hormone-related protein (PTHrP) (1-34) or 10(-4) M N6,2'-O-dibutiryl cyclic AMP before BLM isolation, did not modify the ATP-dependent calcium uptake by BLM vesicles compared with control membranes. However, our results do not rule out that the stimulated ATP-dependent calcium influx in BLM from W256 tumor-host rats could be mediated by the interaction among PTHrP and other humoral factors. Our findings suggest a possible mechanism for the increased renal calcium reabsorption in this animal model for humoral hypercalcemia of malignancy.

Adenosine Triphosphate↗