This Week in Science

Science  20 Dec 1996:
Vol. 274, Issue 5295, pp. 1983
  1. Premalignant cells in disguise?

    Like other cancers, breast cancer is thought to develop through a series of morphologically distinguishable stages beginning with a benign overgrowth of cells and eventually progressing to invasive cancer. Deng et al. (p. 2057) postulated that breast cancers might also arise from cells that appear morphologically normal. They examined normal breast tissue adjacent to invasive tumors and found that in a subset of cases, the normal tissue contained genetic aberrations (loss of heterozygosity) previously detected only in obviously premalignant or malignant tissues. Whether the presence of these genetic changes in normal tissue is predictive of tumor recurrence remains to be investigated.

  2. Martian update


    In an earlier article, McKay et al. suggested that the occurrence of PAHs (polyaromatic hydrocarbons) and textural and mineralogical features in the martian meteorite ALH84001 were consistent with the presence of past primitive life on mars. A series of technical comments and responses starting on p. 2118 address whether abiotic processes could have instead produced these features.

  3. Greener chemistry

    Two reports focus on ways to minimize the use of environmentally burdensome solvents and reaction by-products (see the news story by Kaiser, p. 2012). Markó et al. (p. 2044) have synthesized a copper-based catalyst for the oxidation of a wide variety of alcohols by oxygen or even air, thus avoiding the use of metal oxides or hydrogen peroxides as the oxidant. McClain et al. (p. 2049) have developed nonionic surfactants that allow supercritical CO2 to be used as a solvent for organic polymers which will allow this replacement solvent to be used in processing applications that use waxes, heavy oils, and other high molecular weight organic molecules.

  4. Caught in films

    Lipids and other molecules with polar head groups and long tails can form monolayer (Langmuir) films on a water surface, but making multilayers requires transfer to a solid substrate. Kuzmenko et al. (p. 2046) have made multilayers at an air-water interface by incorporating a small basic molecule to stabilize the interaction between long-chain molecules with acidic head groups. Structural studies showed that the type of multilayers formed under compression depended on the relative handedness of the two molecules—if both were right handed, trilayers with a crystalline segment were formed, but if the molecules had different handedness, amorphous bilayers with poor chain packing were formed.

  5. Prion templates

    Prion proteins, the suspected causative agent of several inherited and infectious forms of spongiform encephalopathy in animals and humans, are abnormal conformers of host proteins. The normal host form (PrPC) has a high alpha -helical content, whereas the prion form (PrPSc) is composed mainly of beta sheets and can assume different isoforms that have protease-resistant fragments of different sizes. Telling et al. (p. 2079; see the news story by Grady, p. 2010) show that extracts from brains of human patients with prion-associated diseases could induce neurodegeneration in transgenic mice that express the human form of PrP. Moreover, the protease-resistant fragments were of the size characteristic for the human disease. These results indicate that the presence of the PrpSc form redirects folding of the PrP protein and may help to explain how different strains of these proteins could arise and propagate.

  6. Kinase meets potassium channel

    Potassium channel activity affects processes, such as muscle contraction and neuronal integration, and electrophysiological and biochemical studies suggest that their activity can be modulated by serine-threonine kinases. Holmes et al. (p. 2089) noted that the human Kv1.5 potassium channel contains two repeats of the Src homology 3 (SH3) domain. They show that the native and cloned forms of this channel are associated directly with Src tyrosine kinase in human myocardium. Activation of the kinase with v-Src resulted in tyrosine phosphorylation of the channel and suppression of its current.

  7. Fat cell fates

    Differentiation of fat cells is inhibited by cell growth factors such as epidermal or fibroblast growth factors. Hu et al. (p. 2100) show that one of the key components in the transcription control of adipogenesis, peroxisome proliferator-activated receptor g (PPARg), is phosphorylated by mitogen-activated protein (MAP) kinase in cells that were stimulated by different growth factors. Cells expressing a PPARg mutant that could not be phosphorylated were more sensitive to induction of adipogenesis by signals such as insulin.

  8. Class crossover

    T cell receptors (TCRs) “see” foreign peptides complexed with either class I or class II major histocompatibility complex (MHC) proteins. Natural killer (NK) cells do not express TCRs but have activating and inhibitory receptors that bind to class I MHC molecules. Mandelboim et al. (p. 2097) studied such T cell clones that express the NK cell activating receptor (NKAR1). These T cells were isolated during NK cell cloning and were restricted to MHC class II responses. Proliferation of these T cells in response to superantigens increased by 300 to 900% in situations where the NKAR1 receptor could bind class I. This costimulation by class I proteins could help T cells initiate immune responses in the presence of limiting amounts of antigen.