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Human immune interferon (IFN-gamma) differs from leukocyte interferon (IFN-alpha) and fibroblast interferon (IFN-beta) in cell origin, inducing agents, physical and biological properties and amino acid sequence. These differences have led to interest in possible differences in the biological properties of IFN-gamma compared with IFN-alpha and IFN-beta. IFN-gamma has the same broad range of biochemical and biological actions as do IFN-alpha and IFN-beta, although relative potencies vary depending on the cell type and function investigated. There has so far been no direct evidence that IFN-gamma alters normal cell functions differently from other interferons. We report here striking qualitative and quantitative differences in the intracellular response of human fibroblasts to IFN-gamma compared with IFN-alpha and IFN-beta. Two-dimensional gel electrophoresis demonstrates, in addition to the induction of a common group of polypeptides, the existence of a set of polypeptides whose synthesis is uniquely induced by IFN-gamma.

The rapid, quantitative release of astaxanthin and other carotenolds from the yeast PhBffIB rhodozvma is described. Hashed cells are ruptured with dimethylsulfoxide (DMSO) and carotenoids extracted into an organic solvent. Extraction and spectrophotometrlc quantitation of total carotenoids is rapid, reproducible and only small volumes (0.1-2 ml) of culture are required. HPLC analysis in normal phase silica gel column indicates that astaxanthln comprises 65-95~ of the total pigmented carotenoids of £. rhodozvma.

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Radioiodinated mouse interferon-fl (125I-MuIFN-j3) bound with high affinity (Kd = 9.8 X 10-10 M) to plasma membrane of L929 murine fibroblasts (4-6 x 103 receptor sites per cell). The binding was saturable and inhibited by a 100-fold excess of unlabeled but not by excess mouse IFN-y (MuIFN-y). MuIFN-P bound at 40C was very rapidly internalized upon warming of the cells to 370C (t /2 = 1.5 min). Indirect immunoferritin labeling indicated that MuIFNfi was initially located in coated pits and subsequently internalized by receptor-mediated endocytosis. Isolated L929 cell nuclei bound 125I-MuIFN-fl with a 7-fold higher affinity (Kd = 1.4 x 10-10 M) and higher receptor density (about 104 per nucleus) than that for the plasma membrane. Binding to the nuclear membrane was inhibited by a 100-fold excess of unlabeled The multiple effects of interferons (IFNs) on the phenotype of vertebrate cells include the establishment of antiviral resistance, reduction in the rate of cell proliferation, and inhibition or stimulation of the expression of many differentiated cellular functions (1, 2). The primary actions of IFNs to achieve these very different effects remain uncertain, as are the loci of such actions. The first step in the action of IFN is its binding to a specific plasma membrane protein receptor (3-9) located in coated pits (4,8), which are specialized cell membrane formations involved in a highly selective and efficient mechanism of receptor-mediated endocytosis of ligands, such as hormones, serum lipoproteins, antibodies, toxins, and viruses (10, 11). Following binding, IFN can be internalized (3,7,8,12), but subsequent steps in its processing are unclear.Treatment with IFNs at physiological temperatures stimulates the synthesis of many polypeptides (13). Although some enzymes are induced or activated that are important in the inhibition of translation of viral proteins (14, 15), the effects on host cell synthetic activities remain less clear. If IFNs act only at the plasma membrane, second messenger(s) (16,17) or transmembrane signaling must be postulated to mediate such effects. However, if binding can be demonstrated on intracellular structures, such as nuclei, it is possible that IFN molecules can directly affect the functions of target organelles. Certain hormones, such as insulin or steroids (18)(19)(20), epidermal growth factor (21), and polyribonucleotides (22), have been shown to bind to the nuclear membrane, and some exert nuclear effects. In the present study we show by radiolabeling and immunocytochemical techniques that mouse IFN-/3 (MuIFN-03) is very rapidly internalized by the mechanism of receptor-mediated endocytosis and that MuIFN-f3 binds to isolated nuclei of mouse fibroblasts: not only are the nuclear membrane receptors of higher affinity than those on the plasma membrane, but they are also present in greater density.MATERIALS AND METHODS Cells. Mouse L929 fibroblasts were grown in suspension as described (4). After 3 days at 36WC, the cells were centrifuged, washed three times with E...