Ocular complications following I-125 brachytherapy for choroidal melanoma.

Uveal melanoma has traditionally been treated with enucleation, plaque brachytherapy, or external beam radiation. Following the results of the multicenter Collaborative Ocular Melanoma Study (COMS), which established no significant difference in mortality rates between enucleation and brachytherapy, plaque brachytherapy has become the favoured modality given its potential for preservation of vision and the eye. Among the radioisotopes that have been used, iodine-125 (I-125) has become the increasingly popular choice in the United States. However, I-125 brachytherapy is associated with complications, including keratitis, iris neovascularization, neovascular glaucoma, radiation retinopathy, and optic neuropathy. The purpose of this review is to discuss the pathogenesis, clinical presentation, and management of complications related to I-125 plaque brachytherapy for choroidal melanoma.

Retention of maize auxin-binding protein in the endoplasmic reticulum: quantifying escape and the role of auxin.

The localisation of maize (Zea mays L.) auxin-binding protein (ABP1) has been studied using a variety of techniques. At the whole-tissue level, tissue printing indicated that ABP1 is expressed to similar levels in all cells of the maize coleoptile and in the enclosed leaf roll. Within cells, the signals from immunofluorescence and immunogold labelling of ultrathin sections both indicated that ABP1 is confined to the endoplasmic reticulum (ER), none being detected in either Golgi apparatus or cell wall. This distribution is consistent with targeting motifs in its sequence. These observations are discussed with reference to the various reports which place a population of ABP1 on the outer face of the plasma membrane, including those suggesting that it is necessary on the cell surface for rapid, auxin-mediated protoplast hyperpolarisation. We have tested the ER, namely that auxin binding induces a conformational change in ABP1 leading to concealment of the KDEL retention motif. Using double-label immunofluorescence the characteristic auxin-induced rise in Golgi-apparatus signal was found, yet no change in the distribution of the ABP1 signal was detected. Maize suspension cultures were used to assay for auxin-promoted secretions of ABP1 into the medium, but secretion was below the limit of detection. This can be ascribed at least partly to the very active acidification of the medium by these cells and the instability of ABP 1 in solution below pH 5.0. In the insect-baculovirus expression system, in which cell cultures maintain pH 6.2, a small amount of ABP1 secretion, less than 1% of the total, was detected under all conditions, Insect cells were shown to take up auxin and no inactivation of added auxin was detected, but auxin did not affect the level of ABP1 in the medium. Consequently, no evidence was found to support the model for auxin promotion of ABP1 secretion. Finally, quantitative glycan analysis was used to determine what proportion of ABP1 might reach the plasma membrane in maize coleoptile tissue. The results suggest that less than 15% of ABP1 ever escapes from the ER as far as the cis-Golgi and less than 2% passes further through the secretory pathway. Such leakage rates probably do not require a specialised mechanism allowing ABP1 past the KDEL retrieval pathway, but we are not able to rule out the possibility that some ABP1 is carried through associated with other proteins. The data are consistent with the presence of ABP1 both on the plasma membrane and in the ER. The relative sizes of the two pools explain the results obtained with immunofluorescence and immunogold labelling and illustrate the high efficiency of ER retention in plants.

Regulation of synthesis and turnover of maize auxin-binding protein and observations on its passage to the plasma membrane: comparisons to maize immunoglobulin-binding protein cognate.

Electrophysiological experiments have indicated that a fraction of the major auxin-binding protein (ABP1) of maize (Zea mays L.) might be a receptor on the outer surface of the plasma membrane. The predominant location of ABP1 is in the lumen of the endoplasmic reticulum (ER), in accord with its C-terminal KDEL retention signal. Little is known about the biology of the protein in vivo or the rate at which it might pass to the cell surface. We have examined the turnover of ABP1 by in vivo labelling of maize coleoptile sections. After different chase times, ABP1 was immunoprecipitated from detergent-solubilised membrane preparations. Two polypeptides coprecipitated with ABP1. Neither was recognised by any ABP1 antibodies nor by monoclonals to ER retention sequences. The possible significance of these coprecipitating polypeptides is discussed. In addition, we have used a monoclonal antibody to precipitate HDEL proteins from the same membrane preparations. Two dimensional electrophoresis and N-terminal sequencing showed that the major HDEL protein precipitated was a member of the heat-shock-protein 70 family, a homologue of BiP (immunoglobulin-binding protein). We have investigated the turnover of this BiP homologue for comparison with ABP1 and found that both had extended lifetimes, with half-lives greater than 24 h. Use of cordycepin to inhibit transcription indicated that ABP1 mRNA was also long-lived. Synthesis of ABP1 was strongly reduced by heat stress, was reduced a little in response to dithiothreitol and was not markedly changed by tunicamycin. In contrast, BiP synthesis increased markedly in response to tunicamycin and dithiothreitol and increased a little after heat stress.(ABSTRACT TRUNCATED AT 250 WORDS)