Modulation of class I major histocompatibility complex antigen cell-surface stability by transmembrane domain length variation.

Cell surface localization of major histocompatibility complex (MHC) class I proteins is conferred to a large extent by their transmembrane domains (TMs) which exhibit allelic, inter-locus and inter-species variation in both amino acid composition and length. Here, the consequences of TM length variation on trafficking and cell-surface stability were examined using the human MHC class I protein HLA-A2. Transformed B lymphocytes (CIR cells) transfected with an HLA-A2 gene encoding an additional 12 hydrophobic amino acids in the TM exhibited a marked decrease in steady-state cell-surface levels of the HLA-A2 protein relative to cells transfected with the wild-type HLA-A2 gene. Diminished surface expression was observed regardless of the presence or absence of the cytoplasmic domain and could not be accounted for by altered association with beta2-microglobulin. While intracellular trafficking rates were affected by TM length enlargement and/or the absence of cytoplasmic domains, this, as well, could not completely explain the TM length-dependent differential cell-surface levels. Studies using brefeldin A to block transport of HLA-A2 proteins to the cell surface suggested that the diminished cell-surface levels of TM enlarged HLA-A2 proteins was a result of decreased cell-surface stability. A significant negative correlation between cell-surface stability and TM length was observed in a comparison of four HLA-A2 proteins differing only in TM length. Similar studies employing an HLA-A2 protein with the TM of HLA-B27 (which is the same length as the HLA-A2 TM but is only 72% identical) suggested that MHC class I TM length variation, independent of amino acid composition and the cytoplasmic domain, may appreciably affect cell-surface stability.

Application of an integrated rate equation to the inactivation of catalase.

A feature of catalase that has received scant attention in recent years and that may have physiological significance is the peroxide-dependent inactivation of the enzyme. In this article we show how to obtain the second-order rate constant for the inactivation reaction by fitting the reaction progress curve to an integrated rate equation. This method will simplify quantitation of the inactivation and reactivation of catalase. These measurements in tissues with altered metabolic states may reveal new information about the role of catalase in nutrition, aging, and pathology.

Gossypol: a possible male antifertility agent. Report of a workshop.

PIP: Clinical studies on the antifertility effect; site of action; pharmacokinetics and toxicity of gossypol, a yellowish pigment occurring in certain species of cotton plant with a reputed contraceptive effect, were first carried out in 1972. Some 4000 Chinese men had used gossypol contraceptive pill for at least 6 months, and some for more than 4 years. Reported efficacy rate of the pill was 99.89%. Male fertility returned by 3 months after discontinuation of the pill, and there were no apparent serious side effects on the babies borne by the wives of the men who had stopped using gossypol. A study by Lee and Malling suggests that gossypol works by inhibiting an enzyme that has a crucial role in the metabolism of sperm and sperm-generating cells. Gossypol is toxic to nonruminant animals, including humans. This toxicity has precluded the economic utilization of cottenseed product for human nutrition. Cottenseed oil, however, is used in food preparation and cooking as salad oil, shortening, and margarine. The mechanism of gossypol's toxicity is not well understood. Toxicity may be due to the action of gossypol on specific enzymes, or interference with amino acid, protein, or iron metabolism. Clinical research suggest that increasing the dietary level of quality of protein minimizes or eliminates the physiologic effects of ingested gossypol within limits. If human reaction to gossypol is similar to that of animal reaction, a diet lacking adequate levels of protein, iron or certain minerals could adversely affect its efficacy and safety, and malnutrition could severely affect gossypol toxicity and its antifertility factors. Carefully designed clinical trials should be done to determine dose-response, efficacy, side effects, metabolic effects, and reversibility potential of gossypol. If gossypol is found to be a new non-steroidal contraceptive method which could be highly effective and reversible, fully safe and inexpensive, it could very well be the answer to the world's population problem.^ieng

Senescent fibroblasts as feeder cells for lymphoid cell cloning.

Senescent primary human skin fibroblasts were used as feeder layers for cloning lymphoid cells by limiting dilution. B-cells including mouse hybridoma cells, human multiple myeloma cells C1R and DIG, as well as an immortalized T-cell line (Jurkat cells) were cloned using this approach. From heterogenous populations, homogeneous (clonal) populations were obtained and further analyzed. The major advantages of senescent fibroblasts as feeder cells are (i) the need to establish primary cultures from experimental animals for preparing feeder cells is obviated; (ii) the risk of contamination with infectious agents is diminished; (iii) primary skin fibroblasts are easily maintained in culture, can be kept at confluence for extended periods of time, and do not undergo spontaneous transformation; and (iv) lymphoid cells are readily separated from fibroblast monolayers. The use of senescent fibroblasts overcomes limitations inherent with primary mouse cell cultures and irradiated cells commonly used as feeder cells in cloning techniques.