Protein kinase C, the major phorbol ester receptor, was purified from bovine brain and through the use of oligonucleotide probes based on partial amino acid sequence, complementary DNA clones were derived from bovine brain complementary DNA libraries. Thus, the complete amino acid sequence of bovine protein kinase C was determined, revealing a domain structure. At the amino terminal is a cysteine-rich domain with an internal duplication; a putative calcium-binding domain follows, and there is at the carboxyl terminal a domain that shows substantial homology, but not identity, to sequences of other protein kinase.

The phorbol-ester-induced loss of protein kinase C that has been documented in many cell types appears to be a critical event in the generation of a cellular refractory state. We have investigated here the synthesis and degradation of the protein kinase C polypeptide in order to determine why its steady-state amounts are depleted in response to phorbol esters. These results indicate that depletion is due to an increased rate of degradation, with no change either in mRNA amounts or in rates of polypeptide synthesis.

A monoclonal antibody of the IgG class, EGFR1, has been isolated using cells of the epidermoid carcinoma line A431 as immunogen. The A431 antigen recognized by EGFR1 has an apparent molecular weight of approximately 175,000, is a cell-surface molecule which can be specifically cross-linked to EGF, exhibits an EGF-stimulated protein kinase activity, binds to EGFR1 in a number of human cell lines to a degree which parallels EGF binding, and shows EGF-dependent internalization in A431 cells and human fibroblasts. We therefore conclude that EGFR1 is directed against an antigenic site on the human EGF receptor. EGFR1 is not mitogenic for human fibroblasts and does not inhibit EGF binding under a variety of assay conditions. The characterization of EGFR1 has allowed the unambiguous assignment of the structural gene for the human EGF receptor to chromosome 7. Preliminary results suggest that a convenient method for isolating a range of anti-EGF receptor monoclonal antibodies can be developed, based on a hybridoma supernatant screening assay in which positive supernatants bind selectively to a human-mouse cell hybrid containing human chromosome 7.

Antisera have been raised against human protein kinase C and also against a synthetic peptide based on the sequence of the bovine brain enzyme (LLNQEE-GEYYNVPIPE). These antibodies react with protein kinase C from a number of species (human, murine, rat, rabbit, bovine), indicating substantial conservation of epitopes. These antisera have been used to quantitate directly protein kinase C by immunoblot analysis. We show here that there is a strict correlation between the levels of immunoreactive polypeptide and extractable calcium- and phospholipid-dependent kinase activity for various cell lines. Treatment of murine, rat, and human cells with phorbol dibutyrate was found to deplete levels of immunoreactive protein kinase C severely. A detailed study of the time course of this depletion in Swiss 3T3 cells shows that it follows precisely the loss of extractable activity. On exposure to 400 nM phorbol 12,13-dibutyrate protein kinase C was essentially undetectable by 40 hours; the half-life of this down-regulation was 6.7 hours. This data thus demonstrate that the loss of immunoreactive protein kinase C and of extractable calcium- and phospholipid-dependent kinase activity precisely parallels the phorbol ester induced down-regulation of binding and responsiveness in Swiss 3T3 cells.

Alternative oxidase activity (cyanide-insensitive respiration) was measured in mitochondria from the shoots, roots, and nodules of soybean (Glycine max L.) and siratro (Macroptiiium atropurpureum) plants. Activity was highest in the shoots and lowest in the nodules. Alternative oxidase activity was associated with one (roots) or two (shoots) proteins between 30 and 35 kilodaltons that were detected by western blotting with a monoclonal antibody against Sauromatum guttatum alternative oxidase. No such protein was detected in nodule mitochondria. Measurements of oxygen uptake by isolated soybean root and nodule cells in the presence of cyanide and salicylhydroxamic acid indicated that alternative oxidase activity was confined to the uninfected cortex cells of the nodule. Immunoprecipitation of translation products of mRNA isolated from soybean shoots revealed a major band at 43 kilodaltons that is assumed to be the precursor of an altemative oxidase protein. This band was not seen when mRNA from nodules was treated in the same fashion. The results indicate that tissue-specific expression of the alternative oxidase occurs in soybean and siratro.

We created a website for patients and families that allowed them to review clinic test results, review educational materials related to these results and post questions to their diabetes educator. Fingerstick haemoglobin A(1c) (HbA(1c)) testing and periodic use of a continuous glucose monitoring system (CGMS) were offered to all patients. The HbA(1c) and CGMS results were posted to the website after each clinic visit. A total of 52 patients with type 1 diabetes were enrolled in the study. There were 16 patients with HbA(1c) values within ADA guidelines and 16 with HbA(1c) values above guidelines; 20 patients were excluded for various reasons. Users of the website were defined as families who logged in four or more times over the six-month study period. For patients whose HbA(1c) started above ADA guidelines, the mean HbA(1c) for website users decreased from 10.5% (SD 2.2) at baseline to 9.1% (SD 1.2) after six months. In the non-users, the mean HbA(1c) increased from 9.5% (SD 1.5) at baseline to 10.4% (SD 2.5). However, these changes were not significant. A between groups comparison (users versus non-users) showed a significant improvement in HbA(1c) for website users (P = 0.03). This change in HbA(1c) was clinically relevant. Further studies with more patients are needed to see if these improvements can be sustained over a longer period.

No abstract

A monoclonal antibody to protein kinase C is described that recognises the site of limited proteolysis on the native enzyme. Binding of the antibody to the purified kinase in vitro blocks partial proteolysis by trypsin, and introduction of the Fab fragment into a rodent glioma cell line inhibits phorbol-ester-induced down-regulation of the kinase. These observations are discussed in the context of the domain structure of protein kinase C and the agonist-induced proteolysis of the kinase in vivo.Protein kinase C is a calcium-dependent and phospholipid-dependent enzyme that is activated in vivo by the lipid diacylglycerol (reviewed in [l]). This neutral lipid is produced in response to a variety of hormones and growth factors through the breakdown of phosphatidylinositols (reviewed in [2]). Thus this enzyme is thought to play a central role in signal transduction from a number of receptor-linked agents.In vitro diacylglycerol activates protein kinase C by increasing the affinity of the enzyme for both calcium and phosphatidylserine [3]. This activation can also be effected by certain tumour promoters [4] which appear to compete for the diacylglycerol-binding site [5]. The amino acid residues involved in the binding sites for diacylglycerol, calcium and phospholipid are yet to be defined although the complete primary structure of protein kinase C has been determined for a number of species [6 -lo]. This sequence information has been used to define a putative domain structure for the enzyme which can be divided into an aminoterminal regulatory and a carboxyterminal catalytic domain joined by a hinge region [6]. There is evidence that cleavage of protein kinase C in vitro generates two functional fragments equivalent to these domains [6,11, 121. In vivo there is also evidence that agonistinduced generation of a catalytic fragment of the enzyme occurs [II, 13, 141.In order to probe the correlation between structure and function for protein kinase C, we have generated mouse monoclonal antibodies that recognise the enzyme. We describe here one such monoclonal antibody. The antigenic epitope is mapped to the region of the molecule vulnerable to tryptic attack and monoclonal antibody binding is shown to inhibit proteolysis both in vitro and in vivo. EXPERIMENTAL PROCEDURE MaterialsAdjuvants were purchased from Difco Laboratories. RPMI 1640 and foetal calf serum from Gibco, England. Hypoxanthine, aminopterin, thymidine, bovine serum albumin, Triton X-100, Tween-20, 2-mercaptoethanol, o-phenylenediamine, phorbol 12-myristate 13-acetate, m-dithiothreitol and trypsin inhibitor, were from Sigma Chemical Co. Ltd (Poole, England). Trypsin was supplied by Worthington Diagnostic Systems Inc. All radioisotopes were supplied by Amersham International (Amersham, Bucks, England). Protein-A -Sepharose CL4B was supplied by Pharmacia (Sweden). The Bio-Dot microfiltration apparatus and transblot cell were from Bio-Rad Laboratories. Isotyping sera and rabbit anti-(mouse immunoglobulin) were from Miles Laboratories (Slough, England). Simia...