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C L Ashendel

Publications and source records attributed to C L Ashendel.

At least 37 records · Page 2Linked to original sources
PubMed1991

Inhibition of myogenesis by the H-ras oncogene: implication of a role for protein kinase C.

Expression of the oncogenic form of H-ras p21 in the mouse myogenic cell line, 23A2, blocks myogenesis and inhibits expression of the myogenic regulatory factor gene, MyoD1. Previous studies from a number of laboratories have demonstrated that the activation of ras p21 is associated with changes in phospholipid metabolism that directly, or indirectly, lead to elevated levels of intracellular diacylglycerol and the subsequent activation of protein kinase C (PKC). To assess the importance of PKC activity to the ras-induced inhibition of skeletal myogenesis, we examined the levels of PKC activity associated with the terminal differentiation of wild-type myoblasts and with the differentiation-defective phenotype of 23A2 ras cells. We demonstrate that there is a 50% reduction in PKC activity during normal myogenesis and that PKC activity is required for myoblast fusion, but not for the transcriptional activation of muscle-specific genes. In contrast, we found that the differentiation-defective 23A2 ras cells possess two- to threefold more PKC activity than wild-type myofibers and that reducing the PKC activity in these cultures does not reverse their non-myogenic phenotype. On the other hand, if PKC activity is downregulated in 23A2 cells before the expression of activated ras p21, myogenesis is not inhibited. These results suggest that activated ras p21 relies on a PKC-dependent signal transduction pathway to initiate, but not to sustain, its negative effects on 23A2 skeletal myogenesis and underscore the potential importance of PKC activity to the proper control of skeletal muscle differentiation.

Animals↗
PubMed1990

Partial characterization of epidermal protein kinase C in mice sensitive or resistant to phorbol ester.

The present study has characterized several aspects of the mouse epidermal protein kinase C (PKC) system and compared phorbol ester-sensitive and -resistant mice. Protein immunoblots of partially purified epidermal PKC preparations from SENCAR and C57BL/6 mice indicated the presence of the gamma-, beta-, and alpha-isozymes of PKC in both strains. Hydroxylapatite chromatography profiles of epidermal PKC isozymes from SENCAR and C57BL/6 mice revealed three major peaks of PKC activity eluting in fractions similar to those observed in chromatograms of brain tissue and corresponding to PKC-gamma, -beta, and -alpha. Further analyses of hydroxylapatite chromatography fractions revealed that PKC-gamma and -beta were present in approximately similar proportions and were much more abundant than PKC-alpha. This distribution of epidermal PKC isozymes was similar in both strains. After a single topical application of 3.4 nmol 12-O-tetradecanoylphorbol-13-acetate (TPA) to SENCAR mouse epidermis, total PKC activity in the cytosol fraction decreased rapidly to about 50% of control within 15 min and was accompanied by an increase (approximately 150% of control) of PKC activity in the membrane fraction. At 4 h, PKC activities were significantly lower than the control levels and remained downregulated through 96 h with a maximal decrease (to approximately 25-30% of the control) in both cytosol and membrane fractions at h. PKC activity returned to control levels by 168 h. Ca++/phospholipid-independent kinase activity was the same as control levels at 15 min, 1 h, and 4 h after TPA treatment but was elevated above control levels at 24 h, 48 h, and 96 h, and by 168 h returned essentially to control levels. No differences were found in the magnitude or kinetics of TPA-induced translocation and downregulation of total PKC or appearance of Ca++/phospholipid-independent kinase activity between SENCAR, DBA/2, and C57BL/6 mice. Scatchard analyses using a two binding site model revealed that the apparent Kd and Bmax values for binding of PDBu to epidermal cytosol and membrane fractions were similar between SSln, SENCAR, DBA/2, and C57BL/6 mice. The present results demonstrate for the first time that mouse epidermis contains significant amounts of the three major PKC isozymes that are present in brain, especially PKC-gamma. In addition, topical application of a promoting dose of TPA did not lead to complete loss of PKC activity in either the membrane or cytosol fractions of mouse epidermis. In conclusion, no differences were observed between phorbol ester-sensitive and -resistant mice in any aspect of epidermal PKC examined.

Animals↗
PubMed1989

Differential responsiveness to phorbol esters correlates with differential expression of protein kinase C in KG-1 and KG-1a human myeloid leukemia cells.

The KG-1 myeloid leukemia cell line differentiates into macrophages in response to 12-O-tetradecanoylphorbol 13-acetate (TPA), while its spontaneous variant, the KG-1a cell line, is resistant to the differentiative effects of TPA. To determine the mechanism underlying these differential responses to TPA, experiments were performed to determine the relative numbers of TPA binding sites, protein kinase C (PKC) enzyme activity levels, PKC translocation responses and PKC gene expression in these cell lines. KG-1a cells exhibited 40% fewer high affinity binding sites for TPA than KG-1 cells. Although PKC translocation from cytosol to the membrane fraction was observed in both cell types, total PKC activity, measured in vitro using type III-S histone as substrate, was reduced by 70% in KG-1a cells. These biochemical differences between the parental line and the phorbol ester non-responsive variant were correlated with the depressed level of PKC-beta RNA abundance in KG-1a cells. Both lines expressed PKC-alpha RNA at comparable levels. Chronic exposure to TPA resulted in down-regulation of PKC enzyme activity in both cell lines, and a selective decrease in PKC-beta RNA transcripts in both cell types. In contrast, chronic TPA treatment had no effect on the levels of PKC-alpha RNA in KG-1 and KG-1a cells. Our results indicate a correlation between the level of PKC-beta expression and the responsiveness of myeloid lineage precursor cells to the differentiative effects of TPA.

Caenorhabditis elegans Proteins↗
PubMed1988

Partial down-regulation of protein kinase C in C3H 10T 1/2 mouse fibroblasts transfected with the human Ha-ras oncogene.

Biochemical and immunological comparison of mouse C3H 10T 1/2 fibroblasts and C3H 10T 1/2 fibroblasts transfected with human activated Ha-ras oncogene indicated significantly lower levels of protein kinase C (PKC) activity and protein in the ras-transfected cells. This effect was observed in three clonal cell lines transfected with an activated ras oncogene. Cytosolic extracts of the ras-transfected cells contained calcium-activated, phospholipid-dependent protein kinase (PKC) activity at 61% of the level of activity present in C3H 10T 1/2 cells. A similarly decreased level of phorbol ester-binding activity was observed in these cells. Analysis of the subcellular distribution of PKC activity in cells failed to indicate significant differences between these cell lines. Immunoblots showed a lower abundance of the Mr 80,000 PKC in ras-transfected cell homogenates and extracts compared to C3H 10T 1/2 cells. Both C3H 10T 1/2 cells and cells transfected with ras expressed only one of the PKC isozymes as resolved by hydroxylapatite chromatography demonstrating that ras transfection of cells did not induce expression of alternative PKC isozymes. These observations indicate that PKC was partially down-regulated in ras-transfected cells, perhaps resulting from constitutively elevated levels of products of phosphatidylinositol-4,5-bisphosphate hydrolysis. Although C3H 10T 1/2 cells were previously shown to be distinct from NIH 3T3 cells in their sensitivity to transformation by the T24-ras oncogene, ras transformation appears to partially down-regulate PKC in C3H 10T 1/2 cells in a manner identical to that for ras-transformed NIH 3T3 cells. This indicates that down-regulation of PKC directly results from the expression of an activated ras oncogene independently of cellular sensitivity to transformation by expression of ras. The common action of ras transformation and phorbol esters to down-regulate PKC provides a possible mechanism for synergism during multistage carcinogenesis.

Animals↗
PubMed1988

Differing modulation of protein kinase C by bryostatin 1 and phorbol esters in JB6 mouse epidermal cells.

Bryostatin 1 (Bryo), a macrocyclic lactone, stimulates some but not all of the biologic effects which are induced by phorbol esters (PEs). In vitro, it competes with PEs for binding to whole cells and activates the calcium/phospholipid-dependent protein kinase, PK-C. To examine whether Bryo, like PEs, is able to stimulate the nonadherent growth of cells, we used the mouse epidermal cell line JB6, which is stimulated by PEs to grow in soft agar. Like PEs, Bryo stimulates both the adherent and nonadherent growth of these cells, but Bryo (0.001-1 microM) is less active than equivalent concentrations of PEs. To attempt to explain the biologic differences between these two agents, we examined the modulation of PK-C by both PEs and Bryo. In a phosphotransferase assay using partially purified PK-C from JB6 cells, Bryo (1-0.001 microM) stimulated less phosphorylation of histone substrate than did PMA. Also, when whole cells were treated with equal concentrations of Bryo or PMA, Bryo stimulated a decreased loss of PK-C from the cytosol. Using purified isozymes of PK-C from rat brain, Bryo demonstrated identical competition to PMA for binding to forms alpha and gamma but decreased binding to form beta. Hydroxylapatite chromatography of JB6 cytosol demonstrated that these cells contain largely peak 2, or beta-PK-C. Although Bryo more weakly activates PK-C from JB6 cells, prolonged exposure of JB6 cells to either 1.0 or 0.01 microM Bryo caused a more rapid loss of immunologically detectable PK-C than did similar concentrations of PEs. We conclude that Bryo is capable of stimulating both the nonadherent and the adherent growth of JB6 cells in a similar fashion to phorbol esters. The differences in biologic effects of Bryo and PMA may be partially explained by Bryo's modulation of PK-C.

Animals↗
PubMed1986

Mechanism of phorbol ester activation of calcium-activated, phospholipid-dependent protein kinase.

Tumor-promoting phorbol esters activated a calcium-activated, phospholipid-dependent protein kinase by direct complexation with this protein kinase and phospholipid in the presence of divalent cations and this complexation was identical to association of kinase/receptor activity with cell membranes. Treatment of isolated mouse spleen lymphocytes with phorbol ester tumor promoters resulted in a rapid shift in the subcellular localization of both the phorbol ester receptor and a calcium-activated, phospholipid-dependent protein kinase activity. Both activities shifted from almost entirely soluble to largely membrane-associated, which is consistent with a single protein possessing both activities. Activation of partially purified kinase/receptor activity by phorbol ester or calcium alone or in combination occurred in parallel to the formation of a complex between the kinase/receptor and phospholipid. Magnesium also was important both for complex formation and for activation of the protein kinase. Although phorbol ester did not appear to affect the affinity of the kinase/receptor for phospholipid, it did increase the extent of formation of a stable complex between the receptor and the phospholipid. These observations support the hypothesis that the cell membrane is the locus of action of both the phorbol esters and the calcium-activated, phospholipid-dependent protein kinase activity.

Animals↗
PubMed1983

Identification of a calcium- and phospholipid- dependent phorbol ester binding activity in the soluble fraction of mouse tissues.

A soluble cytosolic protein which specifically and with high affinity binds tumor promoting phorbol ester tumor promoters was found in mouse tissues Calcium and phosphatidyl serine had to be included in the binding assay to obtain maximal binding activity by the soluble receptor. Soluble binding activity levels paralleled the levels of membrane associated binding activity with the soluble activity accounting for 27% to 80% of the total. Except the calcium and phospholipid requirement, no difference was found between the soluble and membrane associated receptors, suggesting that they are the same protein which can move between the soluble cytosol and cell membranes.

Animals↗
PubMed1983

Observations on the mechanism of skin tumor promotion by phorbol esters.

Data from three different sorts of experiments that were designed to provide additional information on the mechanism of tumor formation are presented. The aim of the first approach was to obtain further evidence for the possible relevance of the induction of ornithine decarboxylase (ODC) activity to tumor promotion by 12-O-tetradecanoylphorbol-13-acetate (TPA) in mouse skin. The irreversible inhibitor of ODC activity, alpha-difluoromethylornithine, not only prevented ODC activity in a dose-dependent manner following skin application, it also prevented skin tumor promotion by TPA. Because in tumor promotion experiments TPA must be applied repetitively in order to elicit tumors, the effect of various time intervals between two or more applications on ODC induction and polyamine levels was investigated. Double applications at intervals greater than 48 hr led to a larger induction of ODC than after a single application. In contrast, at intervals of 24 hr or less, the first application caused a refractory state; the second application did not induce ODC activity even at times after ODC activity had returned to the very low, control activity. The aim of the third approach was to more directly determine the function of TPA in the promotion process by identifying the receptor(s) for TPA and to ascertain the function of the receptor(s). A receptor was purified from the particulate protein fraction of mouse brain and it was found that divalent calcium and phosphatidylserine were essential for the maintenance of binding activity during purification. Furthermore the receptor copurified with protein kinase C; it may be that a TPA receptor is protein kinase C and that TPA activates phosphorylating activity.

Adenosylmethionine Decarboxylase↗
PubMed1983

Solubilization, purification, and reconstitution of a phorbol ester receptor from the particulate protein fraction of mouse brain.

The protein that specifically binds 12-O-[3H]tetradecanoyl-phorbol-13-acetate was solubilized from mouse brain particulate protein with detergents and purified to apparent homogeneity by chromatograph on diethylaminoethyl-cellulose, hydroxylapatite, phenyl agarose, and gel filtration. The purified binding activity consisted of a single polypeptide of apparent molecular weight of 70,000. The isolated receptor protein required reconstitution with phospholipid and cations for binding. The solubilization, isolation, and reconstitution of the receptor did not alter its relative affinity for several different phorbol esters. The isolation of the receptor will aid the determination of both its biological function and its extent of involvement in tumor promotion and cellular physiology.

Animals↗
PubMed1983

Protein kinase activity associated with a phorbol ester receptor purified from mouse brain.

Protein kinase activity copurified with the receptor for 12-O-[3H]tetradecanoylphorbol-13-acetate during its purification from mouse brain particulate protein. All attempts to resolve the protein kinase activity from the receptor were unsuccessful. The isolated receptor required phospholipid and divalent calcium for maximal protein kinase activity. The protein kinase was not activated by cyclic nucleotides or calmodulin. There are striking similarities between the receptor-associated protein kinase activity and the calcium- and phospholipid-dependent protein kinase, which has been suspected of mediating the effects of biological stimuli associated with increased phosphatidylinositol turnover.

Animals↗
PubMed1983

Inhibition of 7-bromomethylbenz[a]anthracene-promoted mouse skin tumor formation by retinoic acid and dexamethasone.

Retinoic acid, a potent inhibitor of mouse skin tumor promotion by 12-O-tetradecanoylphorbol-13-acetate, fails to inhibit tumor formation by the complete carcinogen, 7, 12-dimethylbenz[a]anthracene (DMBA). To obtain further clues about the nature of the mechanism of the carcinogenic process as well as the mechanism of the effect of retinoic acid on tumor promotion, the effect of retinoic acid and two other modifiers (dexamethasone and 7,8-benzoflavone) of tumor formation on tumor promotion by 7-bromomethylbenz[a]anthracene (BrMBA) was determined. BrMBA, a structural analogue of DMBA, is a weak mouse skin tumor-initiating agent but is a good skin tumor promoter. Application of 10, 100, and 200 nmol of BrMBA twice weekly to DMBA-initiated skin resulted in 0, 1.6, and 2.5 papillomas per mouse, and 0, 44, and 60% of mice had papillomas at the 25th week of promotion treatment, respectively. Application of 17 nmol of retinoic acid or 76 nmol of dexamethasone 30 min prior to each twice weekly application of 100 nmol of BrMBA to DMBA-initiated skin inhibited the formation of skin papillomas by 73 and 100%, respectively. 7,8-Benzoflavone, at a 367-nmol dose, did not inhibit tumor promotion by BrMBA. Application of 200 nmol of BrMBA to mouse skin induced epidermal ornithine decarboxylase activity; a peak activity was observed between 8 and 18 hr following BrMBA treatment. Application of 17 nmol of retinoic acid or 76 nmol of dexamethasone inhibited the induction of ornithine decarboxylase activity by BrMBA. 7,8-Benzoflavone did not inhibit the induction of ornithine decarboxylase activity by BrMBA. Retinoic acid and dexamethasone, which inhibit tumor promotion by 12-O-tetradecanoylphorbol-13-acetate, also inhibited tumor promotion by BrMBA, but the nature of the mechanism of tumor promotion by BrMBA is unclear; BrMBA did not inhibit specific binding of 12-O-[3H]tetradecanoylphorbol-13-acetate to the cellular membrane fraction of mouse epidermis.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1982

Specific high-affinity binding of the phorbol ester tumor promoter 12-O-tetradecanoylphorbol-13-acetate to isolated nuclei and nuclear macromolecules in mouse epidermis.

The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) binds reversibly and with high affinity and specificity to nuclear macromolecules in mouse epidermis. The dissociation constants determined from Scatchard analysis of epidermal nuclei and nuclear macromolecules are 3.58 +/- 0.66 (S.E.) and 2.18 +/- 0.54 nM, respectively. The solubilization of TPA receptors from epidermal nuclei by DNase I was examined. Following a 20-min digestion at 22 degrees, more than a 2-fold increase in specific TPA binding was observed in the supernatant relative to non-nuclease-treated nuclei (0.71 versus 0.32 pmol/mg protein, respectively). Our data indicate that epidermal nuclei contain saturable and specific TPA-binding macromolecules and that these binding components may be associated with regions of chromatin that are preferentially susceptible to nucleolytic cleavage. These data suggest the existence of nuclear receptors for the phorbol ester tumor promoters. These observations may necessitate a more critical assessment of plasma membrane binding as the sole binding site responsible for triggering the multistep process of tumor promotion in mouse epidermis.

Animals↗
PubMed1982

Mouse skin: a useful model system for studying the mechanism of chemical carcinogenesis.

Mouse skin has a long history as a useful model for the study of the mechanism of carcinogenesis (6). In particular, the availability of specific diterpene esters has made possible rapid progress in understanding the mechanism of tumor formation (4,6,8,19,36,41), although certain details may be unique to promotion by phorbol esters. Evidence is compatible with an essential role for elevated levels of polyamines in tumor promotion, but other components of phorbol ester action on mouse skin are also essential (27,40,54). These may include the production of dark cells (22), inhibition of maturation (2,19,41), and the elimination of metabolic cooperation (12,57). Factors modifying biochemical processes that are essential to tumor formation produce a parallel effect on tumor formation. Some of these inhibitors act synergistically to inhibit tumor formation (50,55), and knowledge of their action may lead to practical application for the prevention of human cancer.

9,10-Dimethyl-1,2-benzanthracene↗