Protein Kinase C (PKC) isoforms have been identified as major cellular signaling proteins that act directly in response to oxidation conditions. In retina and lens two isoforms of PKC respond to changes in oxidative stress, PKCγ and PKCε, while only PKCε is found in heart. In heart the PKCε acts on connexin 43 to protect from hypoxia. The presence of both isoforms in the lens led to this study to determine if lens PKCε had unique targets. Both lens epithelial cells in culture and whole mouse lens were examined using PKC isoform-specific enzyme activity assays, coimmunoprecipitation, confocal microscopy, immunoblots, and light and electron microscopy. PKCε was found in lens epithelium and cortex but not in the nucleus of mouse lens. The PKCε isoform was activated in both epithelium and whole lens by 5% oxygen when compared to activity at 21% oxygen. In hypoxic conditions (5% oxygen) the PKCε co-immunoprecipitated with the mitochondrial cytochrome C oxidase IV subunit (CytCOx). Concomitant with this the CytCOx enzyme activity was elevated and increased co-localization of CytCOx with PCKε was observed using immunolabeling and confocal microscopy. In contrast, no hypoxia-induced activation of CytCOx was observed in lenses from the PKCε knockout mice. Lens from 6 week old PKCε knockout mice had a disorganized bow region which was filled with vacuoles indicating a possible loss of mitochondria but the size of the lens was not altered. Electron microscopy demonstrated that the nuclei of the PCKε knockout mice were abnormal in shape. Thus, PKCε is found to be activated by hypoxia and this results in the activation of the mitochondrial protein CytCOx. This could protect the lens from mitochondrial damage under the naturally hypoxic conditions observed in this tissue. Lens oxygen levels must remain low. Elevation of oxygen which occurs during vitreal detachment or liquification is associated with cataracts. We hypothesize that elevated oxygen could cause inhibition of PKCε resulting in a loss of mitochondrial protection.

A quantitative microbiological assay and a bioautography system with Penicillium avellaneum UC-4376 was developed for the antitumor drugs maytansine, and its homologues, maytanprine and maytanbutine. The susceptibility of the assay is 1.5 μg/ml.