Inositol 1,3,4,5-tetrakisphosphate induces Ca2+ sequestration in rat liver cells.

Inositol 1,4,5-trisphosphate [I(1,4,5)P3] is a second messenger generated along with diacylglycerol upon the binding of various physiological agents with their cell surface receptors. I(1,4,5)P3 mobilizes Ca2+ from intracellular storage sites through a receptor-coupled mechanism, and the subsequent increased intracellular free calcium ion concentration [( Ca2+]i) activates a multitude of cellular responses. Electropermeabilized neoplastic rat liver epithelial (261B) cells were used to study Ca2+ sequestration, a process that reverses the elevated [Ca2+]i to resting levels and replenishes intracellular Ca2+ pools. Although I (1,4,5)P3-mobilized Ca2+ is readily sequestered into storage pools by the action of Ca2+-adenosine triphosphatases, Ca2+ mobilized by addition of the nonmetabolized inositol trisphosphate isomer I(2,4,5)P3 is not sequestered, suggesting that metabolism is necessary to eliminate the stimulus for Ca2+ release. Several inositol phosphate compounds were examined for their ability to lower the buffer [Ca2+] to determine if a specific I(1,4,5)P3 metabolite might be involved in stimulating Ca2+ sequestration; of these, I(1,3,4,5)P4 alone was found to induce Ca2+ sequestration, demonstrating a physiological role for this inositol trisphosphate metabolite.

PDGF-induced activation of phospholipase C is not required for induction of DNA synthesis.

Platelet-derived growth factor (PDGF) induction of DNA synthesis is believed to involve activation of phospholipase C (PLC) and subsequent accumulation of inositol 1,4,5-triphosphate [I(1,4,5)P3], increase in intracellular Ca2+, activation of protein kinase C (PKC), and receptor down regulation. Generation of these events is triggered by the tyrosine protein kinase (TPK) activity of the PDGF receptor. The TPK inhibitor genistein blocked PDGF induction of these events, including DNA synthesis, with the exception of receptor down regulation. PDGF-induced phosphotyrosine phosphorylations, including receptor autophosphorylation, were inhibited by genistein. Removal of genistein and PDGF resulted in DNA synthesis without the occurrence of PLC activation. These findings indicate that these early events, with the exception of receptor down regulation, are not necessary for PDGF-induced DNA synthesis.

Epidermal growth factor disrupts gap-junctional communication and induces phosphorylation of connexin43 on serine.

Growth factors regulate cellular proliferation and differentiation by activating plasma membrane tyrosine kinase receptors and triggering a cascade of events mediated by intracellular signaling proteins. The mechanism underlying growth factor modification of cellular functions, such as gap-junctional communication (gjc), has not been established clearly. Addition of epidermal growth factor (EGF) to T51B rat liver epithelial cells resulted in the rapid activation of EGF receptor tyrosine kinase activity followed by a transient dose-dependent disruption of gjc. This change did not result from the gross disturbance of membrane gap junction plaques as measured by immunofluorescence microscopy, but instead correlated with markedly elevated phosphorylation of the connexin43 (cx43) gap junction protein, a profound shift to predominantly phosphorylated forms of cx43, and the appearance of a novel phosphorylated cx43 protein. These changes in cx43 phosphorylation involved only serine residues. On restoration of gjc, these alterations in cx43 phosphorylation reverted to the pre-EGF treatment state. Both events were inhibited by the serine/threonine protein phosphatase inhibitor, okadaic acid. Therefore, unlike the case for pp60v-src, EGF-induced disruption of gjc is not associated with tyrosine phosphorylation of cx43, but instead may result from phosphorylation of cx43 by activated intracellular signaling serine protein kinase(s).

Stimulation of DNA synthesis in calcium-deprived T51B liver cells by the tumor promoters phenobarbital, saccharin, and 12-O-tetradecanoylphorbol-13-acetate.

Extracellular calcium deprivation arrested the proliferative development of T51B rat liver cells in late G1 or S phases. These arrested cells initiated DNA synthesis within an hr after addition of calcium or a tumor promoter such as phorbol-12,13-didecanoate, phenobarbital, saccharin, or 12-O-tetradecanoylphorbol-13-acetate. Nonpromoting relatives of 12-O-tetradecanoylphorbol-13-acetate such as phorbol, 4-O-methyl-12-O-tetradecanoylphorbol-13-acetate, and 4 alpha-phorbol-12,13-didecanoate were unable significantly to induce the calcium-deprived cells to initiate DNA synthesis. It is suggested that an ability to elicit a prompt DNA-synthetic response from calcium-deprived cells might be a useful in vitro indicator of tumor-promoting potential.

Calcium requirements for the proliferation of cells infected with a temperature-sensitive mutant of Rous sarcoma virus.

Between 32 degrees and 39 degrees, uninfected normal rat kidney (NRK) cells proliferated minimally, or not at all, in medium containing 0 to 0.01 mM extracellular free calcium. Transformation of NRK cells by wild-type avian sarcoma virus B77 enabled them to proliferate equally rapidly at all temperatures in high (1.25 mM)- or low (0.001 mM-calcium medium. Transformation by the temperature-sensitive LA-23 mutant of Rous sarcoma virus also enabled NRK cells to proliferate in low (0.001 mM)-calcium medium at 32 degrees or 37 degrees. However, the LA-23 NRK cells could not proliferate in low (0.001 mM)-calcium medium at a nonpermissive temperature such as 39 degrees, which prevents expression of other aspects of the transformed phenotype.

Different extracellular calcium requirements for proliferation of nonneoplastic, preneoplastic, and neoplastic mouse cells.

The DNA-synthetic and proliferative activities of freshly isolated, nontumorigenic C3H mouse skin cells (first passage) were lowest when the extracellular free (or ionic) calcium level was reduced to between 0.05 and 0.1 mM, whereas the extracellular free calcium level in cultures of repeatedly passaged, preneoplastic C3H/10T1/2 and MCA-C3H/10T1/2 type I mouse fetal fibroblasts had to be reduced to 0.01 mM or less before the DNA-synthetic and proliferative activities were minimal. This inhibition of DNA synthesis and cell multiplication by calcium deprivation was rapidly reversed by returning the extracellular calcium level to its normal value. In contrast, the neoplastic fibrosarcoma-forming, MCA-C3H/10T1/2 type III mouse fetal fibroblasts could synthesize DNA and could multiply indefinitely even in the presence of an extremely low concentration of extracellular free calcium. Thus, the extracellular calcium requirement for DNA synthesis and proliferation appears to reflect the tumorigenic potential of the cell.

Reversion of the neoplastic phenotype of human glioblastoma cells by connexin 43 (cx43).

Connexins (cx), structural components of gap junction, are believed to play a role in the regulation of cell proliferation and suppression of the neoplastic phenotype. We used human brain glioblastoma tumor cells as a model system to test this hypothesis. Western blot and reverse transcription-PCR analysis indicate that the expression levels of the gap junction protein connexin 43 (cx43) are profoundly decreased in several human brain tumor cell lines examined. Transfection of human cx43 into human glioblastoma cell lines U251 and T98G profoundly reduces cell proliferation in monolayer culture, in soft agar, and in athymic nude mice. Surprisingly, these effects are not associated with the establishment of gap junction communication in cx43 transfected cells. We conclude that the loss of cx43 expression may play a role in the development of human gliomas and that cx43 acts as a tumor suppressor gene to human glioblastoma.

Inhibition of PDGF-induced c-jun and c-fos expression by a tyrosine protein kinase inhibitor.

The expression of the proto-oncogenes c-fos, c-jun, jun B and jun D was monitored in quiescent C3H10T1/2 fibroblasts after stimulation with PDGF. The mRNA level of c-fos, c-jun and jun B, but not of jun D, was stimulated by PDGF. The inductions were abolished when genistein, a specific tyrosine protein kinase inhibitor, was added concomitantly with PDGF, a condition in which DNA synthesis is known to be inhibited. As already shown previously, treatment with PDGF and genistein for 4h followed by the replacement with fresh medium induces the progression of the cells through the G1 phase of their growth-division cycle, without phospholipase C activation. The removal of PDGF and genistein was accompanied by an important increase in c-fos, c-jun and jun B mRNA expression, which correlated with the entrance of cells into G1 phase. Thus, the proto-oncogene expressions induced by PDGF are also obtained in the absence of phospholipase C activation. This result also suggests that the mRNA levels of c-jun, jun B and to a lesser degree c-fos are positively regulated by tyrosine protein kinase activity, whereas jun D is negatively regulated.

Regulation of Cx43 gap junctions: the gatekeeper and the password.

Gap junctions are regulatable pores that connect the cytoplasms of neighboring cells. Hossain and Boynton focus on connexin 43 gap junctions and their regulation by changing the phosphorylation status of the COOH-terminal domain of connexin 43 or by altering protein-protein interactions in this region. The COOH-terminal domain of connexin 43 appears to be a key player in regulating gap junctional communication (GJC) because many divergent signals in many different cell types modify this domain to inhibit GJC.

Heparin inhibits IP3-induced Ca2+ release in permeabilized pancreatic beta-cells.

Heparin was found to inhibit the Ca2+ release induced by inositol 1,4,5-trisphosphate (IP3) in permeabilized pancreatic beta-cells obtained from obese hyperglycemic mice. The effect of heparin was dose-dependent and not due to inhibition of Ca2+ uptake into the IP3-sensitive pool. The effect appeared specific for heparin and was not reproduced by other polysaccharides such as chondroitin sulfates. Heparin might consequently be a useful tool when investigating the molecular mechanism whereby IP3 mobilizes Ca2+.

Calcium dependence of chemical carcinogen induced morphological transformation of Syrian hamster embryo cells.

The effect of extracellular calcium upon carcinogen induced morphological transformation was evaluated in Syrian hamster embryo cells. Reduction in [Ca2+] from 1.8 mM to 0.2 mM throughout the 6 days between exposure of the cells to 2.5 microgram benzo [a]pyrene (BP)/ml and examination of the cells for transformation inhibited both cell proliferation and transformation as measured by the frequencies of colony formation and morphological transformation. The transformation frequency among surviving cells, i.e. frequency/cell colony, however, was nearly equivalent indicating that the inhibition of transformation largely resulted from inhibition of cell colony formation. Proliferation and transformation were unaffected when [Ca2+] was reduced to 0.2 mM on days 3-6. Reduction to 0.01 mM Ca2+ during the same period, however, completely abolished transformation by BP, UV-irradiation or n-acetoxyacetylaminofluorene (AcAAF) without reducing cell proliferation. Thus, the expression of morphological transformation in newly transformed hamster cells is dependent upon extracellular [Ca2+] to a greater degree than is cell proliferation.

The influence of extracellular calcium on the distribution of protein kinase C in non-neoplastic and neoplastic rat liver cells.

Non-neoplastic T51B rat liver epithelial cells cannot proliferate in Ca2+-deficient medium. This proliferative inhibition in Ca2+-deficient medium is accompanied by a large reduction in the amount of cellular EDTA-extractable Ca2+/phospholipid-dependent protein kinase (protein kinase C) activity. By contrast, tumorigenic epithelial cells from several Morris hepatomas proliferate in Ca2+-deficient medium and either maintain or greatly increase their content of EDTA-extractable protein kinase C.

Relation between colony formation in calcium-deficient medium, colony formation in soft agar, and tumor formation by T51B rat liver cells.

T51B rat liver cells and several carcinogen-treated, carcinogen + saccharin-treated, or spontaneously altered clones of T51B cells were tested for their abilities to form colonies in calcium-deficient medium and soft agar and to produce tumors in athymic nude mice. Most (10 out of 11) of the clones which were derived from colonies in calcium-deficient medium were unable to form colonies in soft agar and 8 out of 11 were non-tumorigenic. Conversely, 6 out of 9 clones derived from colonies in soft agar were unable to multiply significantly in calcium-deficient medium and 5 of these 6 clones were also non-tumorigenic. Two of these 9 soft agar-growing clones were tumorigenic, one of which also proliferated in calcium-deficient medium, and the other of which acquired the ability to proliferate in calcium-deficient medium after it became able to form tumors in athymic nude mice. Thus, T51B rat liver cells gain the ability to grow in calcium-deficient medium and soft agar independently during the process of neoplastic transformation and neither characteristic by itself reliably predicts tumorigenicity.

Oncogenic transformation and the reductions of insulin secretion and proliferative calcium dependence during repeated passage of pancreatic islet cells in vitro.

Islet cells were isolated from 2 fetal bovine pancreas glands and cultivated in vitro. During the course of repeated passage in vitro, the B-cells in these cultures retained the ability to synthesize insulin, but rapidly lost the ability to secrete it. The cells also became progressively more able to proliferate in calcium-deficient medium which did not support the proliferation of cells from primary cultures. The reductions of insulin secretion and proliferative calcium dependence were accompanied by the acquisition of the ability to produce tumors in nude mice.

Regulation of proliferation of normal and neoplastic rat liver cells by calcium and cyclic AMP.

Calcium and cyclic AMP control the proliferation of nontumorigenic liver cells. These agents seem to be cogenerators of a signal to start synthesizing deoxyribonucleotides, the earliest of the DNA synthetic processes. By contrast, calcium has little or no effect on the proliferation of tumorigenic cells in vitro. Some possible reasons for this loss of control are presented, and the usefulness of this property as a tool for the detection of carcinogens is discussed.

Measurement of serum prostate-specific membrane antigen, a new prognostic marker for prostate cancer.

OBJECTIVES: To describe current results with Western blot assay for prostate specific membrane antigen (PSMA) using 7E11.C5 antibody and the development of an additional antibody measurement for PSMA by a new sandwich immunoassay. METHODS: A population of patients from a screening group, from a difficult diagnostic group, from a pre- and postoperative radical prostatectomy group, and from a group with metastatic disease followed for a serial period, provided the serum values for a prospective assessment of PSMA by Western blot assay. A new monoclonal antibody was sought, reacting to the C-terminal region of PSMA in order to develop a sandwich radioimmunoassay. RESULTS: PSMA values in screened patients correlate with the more advanced stage of the cancers determined. In postprostatectomy patients, the PSMA value corresponds more with preoperative values and with the values of those with a poor clinical course. In difficult diagnostic cases, the PSMA value is increased, specifically in hormone-refractory cases and particularly in those cases judged by other criteria, such as the National Prostatic Cancer Project, to be in clinical progression compared with those judged to be in clinical remission. The level of PSMA value appears to be independent of homogeneous tumor volume and to be more related to that of prior hormone treatment, or to where prostate cancer cells can be documented to be outside the prostate. A new monoclonal antibody, 3F5.4G6, reacts with the extracellular domain of PSMA near the C-terminal region. This is in contrast to the previously measured antibody 7E11.C5, which reacts with an N-terminal epitope. 3F5.4G6 recognizes the same PSMA protein as does 7E11.C5. The epitopes are essentially at opposite ends of the molecule. The 3F5.4G6 antibody reacts with the LNCaP line but not with DU145, or PC3. These two antibodies to PSMA are well suited for use in a new sandwich immunoassay. CONCLUSIONS: PSMA provides a prostatic cancer serum test by using Western blot, which suggests a clinical prognostic value not seen with other markers. New antibodies, such as 3F5.4G6, reacting with the extracellular domain of PSMA combined with 7E11.C5, appear to offer an opportunity for a new sandwich immunoassay.

Characterization of natural toxins with inhibitory activity against serine/threonine protein phosphatases.

Recent studies suggest that the ability to inhibit the activity of certain serine/threonine protein phosphatases underlies the toxicity of several natural compounds including: okadaic acid, microcystin-LR, nodularin, calyculin A and tautomycin. To characterize further the actions of these toxins, this study compares the inhibitory effects of okadaic acid, chemical derivatives of okadaic acid, microcystin-LR, microcystin-LA, nodularin, calyculin A and tautomycin on the activity of serine/threonine protein phosphatases types 1 (PP1), 2A (PP2A) and a recently identified protein phosphatase purified from bovine brain (PP3). This study shows that, like PP1 and PP2A, the activity of PP3 is potently inhibited by okadaic acid, both microcystins, nodularin, calyculin A and tautomycin. Further characterization of the toxins employing the purified catalytic subunits of PP1, PP2A and PP3 under identical experimental conditions indicates that: (a) okadaic acid, microcystin-LR, and microcystin-LA inhibit PP2A and PP3 more potently than PP1 (order of potency PP2A > PP3 > PP1); (b) nodularin inhibits PP1 and PP3 at a similar concentration that is slightly higher than that which affects PP2A, and (c) both calyculin A and tautomycin show little selectivity among the phosphatases tested. This study also shows that the chemical modification of the (C1) carboxyl group of okadaic acid can have a profound influence on the inhibitory activity of this toxin. Esterification of okadaic acid, producing methyl okadaate, or reduction, producing okadaol, greatly decreases the inhibitory effects against all three enzymes tested. Further reduction, producing 1-nor-okadaone, or acetylation, producing okadaic acid tetraacetate, results in compounds with no inhibitory activity. In contrast, the substitution of alanine (-LA) for arginine (-LR) in microcystin has no apparent effect on the inhibitory activity against PP1, PP2A or PP3.

Antisense human neuroglia related cell adhesion molecule hNr-CAM, reduces the tumorigenic properties of human glioblastoma cells.

BACKGROUND: Human Nr-CAM (Neuroglia related Cell Adhesion Molecule) is over expressed in glioblastoma multiforme tissue (GMT) as compared to normal brain tissue (NBT). MATERIALS AND METHODS: We transfected a human glioblastoma cell line (2020-CRL) with a vector that overexpresses antisense hNr-CAM using a CMVpromoter. RESULTS: Antisense hNr- CAM caused reduction in the native hNr-CAM expression, changed cell morphology, reduced the cell proliferation rate and lengthening of the cell cycle. Furthermore, antisense hNr-CAM overexpression in these cells caused extensive reduction in the number of soft agar colonies and invasion through extra cellular matrix (ECM) gel in vitro. Subcutaneous injection of antisense hNr-CAM overexpressing glioblastoma cells into nude mice caused complete inhibition of tumor formation as compared to vector only transfected cells. Intra-tumoral inoculation of antisense hNr-CAM expressing plasmid also caused slow tumor growth in nude mice in vivo. CONCLUSION: On the basis of these results, we conclude that hNr-CAM is a valid target for potential gene therapy of glioblastoma tumors.

Cancer immunotherapy for prostate cancer.

Our approach to prostate cancer immunotherapy involves two components dendritic cells as antigen-presenting cells; and the antigen used to target T-cell attack, HLA-A0201-associated peptides from prostate specific membrane antigen (PSMA). We have conducted a phase I dose-ranging study in 51 men with advanced prostate cancer, using dendritic cells pulsed with a PSMA peptide. no significant toxicity was observed. In that study, T-cell response was enhanced, with seven men meeting NCPC and PSA criteria for partial response. We are now conducting a phase II study with 67 men, who will receive 6 infusions of dendritic cells that have been pulsed with 2 PSMA peptides, at 6-week intervals. The phase II study design and rationale is described in this paper.