Calphostins (UCN-1028), novel and specific inhibitors of protein kinase C. I. Fermentation, isolation, physico-chemical properties and biological activities.

Abstract

A novel complex of calphostin (UCN-1028), which specifically inhibits protein kinase C (PKC) has been isolated from the culture broth of a fungi Cladosporium cladosporioides. Purification of individual components was carried out by silica gel, non-porus resin Diaion HP-20SSand Sephadex LH-20 chromatography, leading to isolation of five closely related components, A, B, C, D and I. Calphostinsshowedcytotoxic activities against various tumorcells, andthese cytotoxicities were proportional to their inhibitory activities against PKC. Specific inhibitors of protein kinase C (PKC) can be excellent tools to study the role of PKC in cellular proliferation and differentiation, and are expected to be potential chemotherapeutic agents. In the course of screening new selective inhibitors of PKC, a fungi Cladosporium cladosporioides was found to produce a complex of novel and specific inhibitors of PKC, designated calphostin (originally called UCN-1028). The most hydrophobic component, calphostin A (UCN-1028A) which was the first purified compound, has already been reported1*. Further study of the calphostin fermentation showed the presence of four components in addition to calphostin A. This paper describes the fermentation, isolation, physico-chemical properties and biological activities of the calphostin complex. Materials and Methods Microorganism The producing organism, C. cladosporioides FERMBP-1285 was isolated from a block fence around a house in Osaka, Japan.

Characterization of Activators and Inhibitors of Protein Kinase Cμ

“…In the light of the unusual phorbol ester responsiveness of PKCp, it is revealing that calphostin C, a highly specific inhibitor of various PKC isozymes, was completely ineffective at concentrations known to affect other PKCs [32]. Calphostin C binds to and acts upon light activation via the phorbol ester binding domain [34].…”

“…6A, lane 2). Unexpectedly, calphostin C [32], cur- rently regarded as the most selective inhibitor of PKCs, did not inhibit PKCp autophosphorylation at all (Fig. 6A, lane 6).…”

Metabotropic Glutamate Receptors and Dopamine Receptors Cooperate to Enhance Extracellular Signal-Regulated Kinase Phosphorylation in Striatal Neurons

“…For this analysis, we used three different PKC inhibitors. Calphostin C inhibits PKC by competing with DAG binding sites (Kobayashi et al, 1989). GF109203X is a potent inhibitor of PKC␣ and PKC␤1.…”

α1‐Adrenoceptor activation of PKC‐ε causes heterologous desensitization of thromboxane receptors in the aorta of spontaneously hypertensive rats

“…Pre-incubation with PDBu mimicked the desensitization exerted by phenylephrine, an effect that can be attributed to activation of PKC (Way et al, 2000). Since atypical PKCs cannot be activated by phorbol esters or inhibited by calphostin C (Kobayashi et al, 1989;Bruns et al, 1991;Boehm et al, 1996), the increases in PK-N2 and PKC-ζ mRNA expression observed in the present study are not likely to be responsible for TP receptor desensitization. As regards conventional PKCs, the mRNA expression of PKC-α is higher in SHR than WKY aorta, as it is in the heart where it may be related to hypertrophy (Dorn and Force, 2005).…”