Inhibition of hepatoma cell growth in vitro by arylating and non-arylating K vitamin analogs. Significance of protein tyrosine phosphatase inhibition

We recently found that a thioether analog of K vitamin (Cpd 5) inhibited the activity of protein-tyrosine phosphatases (PTPases) and induced protein-tyrosine phosphorylation in a human hepatoma cell line (Hep3B). We have now examined the structural requirements for induction of protein-tyrosine phosphorylation and PTPase inhibition by several K vitamin analogs. Thioether analogs with sulfhydryl arylation capacity, especially those with a hydroxy (Cpd 5) or a methoxy group at the end of the side chain, induced protein-tyrosine phosphorylation, but non-arylating analogs, such as those with an all-carbon or O-ether side chain, did not. Among the receptor-tyrosine kinases, epidermal growth factor receptors were tyrosine-phosphorylated by treatment with thioether analogs, whereas insulin and hepatocyte growth factor receptors were not. An increase in tyrosine-phosphorylated ERK2 mitogen-activated protein kinase was also observed. The activity of purified T cell PTPase was inhibited only by the thioether analogs, but not by non-arylating analogs. Furthermore, the epidermal growth factor receptor dephosphorylation activity of Hep3B cell lysates was inhibited by Cpd 5 treatment. A similar induction of protein-tyrosine phosphorylation by Cpd 5 was seen in other human hepatoma cell lines together with growth inhibition. However, one cell line (HepG2), which was relatively resistant to growth inhibition by Cpd 5, did not increase its phosphorylation levels upon Cpd 5 treatment. These results suggest that cell growth inhibition by thioether analogs is closely associated with inhibition of PTPases by sulfhydryl arylation and with tyrosine phosphorylation of selected proteins.     

The evolution of cooperation

Darwin recognized that natural selection could not favor a trait in one species solely for the benefit of another species. The modern, selfish-gene view of the world suggests that cooperation between individuals, whether of the same species or different species, should be especially vulnerable to the evolution of noncooperators. Yet, cooperation is prevalent in nature both within and between species. What special circumstances or mechanisms thus favor cooperation? Currently, evolutionary biology offers a set of disparate explanations, and a general framework for this breadth of models has not emerged. Here, we offer a tripartite structure that links previously disconnected views of cooperation. We distinguish three general models by which cooperation can evolve and be maintained: (i) directed reciprocation--cooperation with individuals who give in return; (ii) shared genes--cooperation with relatives (e.g., kin selection); and (iii) byproduct benefits--cooperation as an incidental consequence of selfish action. Each general model is further subdivided. Several renowned examples of cooperation that have lacked explanation until recently--plant-rhizobium symbioses and bacteria-squid light organs--fit squarely within this framework. Natural systems of cooperation often involve more than one model, and a fruitful direction for future research is to understand how these models interact to maintain cooperation in the long term.     

Genetically Distinct Populations of the Dinoflagellate <Emphasis Type="Italic">Peridinium limbatum</Emphasis> in Neighboring Northern Wisconsin Lakes

The extent to which free-living microorganisms exist in geographically isolated, genetically distinct populations is a subject of continuing debate. Some authorities contend that many microorganisms have cosmopolitan distributions, while others provide evidence that more limited geographical distribution of genetically distinct populations can occur. We report the occurrence of two morphologically similar, but genetically distinct, populations of the microbial eukaryote Peridinium limbatum (Stokes) Lemmermann from neighboring Northern Wisconsin freshwater bodies. Five strains of P. limbatum were cultured by single-cell isolation from both Crystal Lake and Crystal Bog (Oneida Co., WI). Genetic variation between the two populations encompassed 8.9% (mean of 35.4 of 397 nucleotides) of the nuclear ribosomal DNA internal transcribed spacer (ITS1 and ITS2) region. In contrast, 0.5% (mean of 2.25 of 397 nucleotides) variation was observed within the Crystal Lake population and 0.3% (mean of 1.21 of 397 nucleotides), within the Crystal Bog population. This difference between the two populations was highly statistically significant (p-value << 0.001). The extent of genetic variation between the two P. limbatum populations was greater than that reported in the literature for some morphologically distinguishable microalgal species, suggesting the occurrence of cryptic sister species. On the other hand, hybrid sequences obtained from one of the Crystal Lake strains suggest that the two populations may still be members of a single sexually compatible biological species. Our data suggest that the two neighboring P. limbatum populations may be diverging genetically under conditions of limited gene flow, suggesting a mechanism for the origin of geographically isolated, genetically distinct populations of microbial eukaryotes.     

Antipredator benefits of group living in colonial web-building spiders: the ‘early warning’ effect

The Mexican colonial web-building spider Metepeira incrassata is frequently attacked by predatory wasps from a number of families. Previous studies have shown that wasps often attack more than one spider during a ‘run’ on a colony, but capture success declines as colony size increases, and that spiders in the central core of the colony have lower risk (Rayor & Uetz 1990, Behavioral Ecology and Sociobiology, 27, 77-85; Uetz & Hieber 1994, Behavioral Ecology, 5, 326-333). We used data from direct observation of attacks and field experiments to test the hypothesis that colonial web-building spiders benefit from ‘early warning’ of predator approach through vibrations in the colony web. Analysis of 135 naturally occurring wasp attack ‘runs’ (attacks on 454 spiders) showed that the per-attack run and per-spider capture success of wasps decreased significantly with increased spider colony size. Spider defensive and evasive behaviours observed in a subset of these attacks varied with the attack sequence. Evasive responses by spiders were more frequent later in the attack, suggesting advance warning of predator approach. Experiments using a predator-simulating vibration source demonstrated that mean reaction distance of spiders increased with increasing colony size. Adult female spiders in core positions reacted at greater distances than those on the periphery, but immature spiders, whose capture risk is lower, showed no difference. Behaviour of spiders during simulated attacks was similar to observed encounters with wasps: evasive responses were more frequent and response latency was shorter in spiders attacked later in the sequence, and in many cases, spiders took evasive action prior to any contact with the stimulus. Additional experiments testing isolated cues (web contact, airborne vibration, web-borne vibration) suggest spiders respond to web-borne vibrations generated by predators and evasive behaviours of other spiders. Together, these results support the ‘early warning’ hypothesis of antipredator benefits for colonial web-building spiders.     

The timing of the "fertile window" in the menstrual cycle: day specific estimates from a prospective study

ObjectivesTo provide specific estimates of the likely occurrence of the six fertile days (the “fertile window”) during the menstrual cycle.DesignProspective cohort study.Participants221 healthy women who were planning a pregnancy.ResultsThe fertile window occurred during a broad range of days in the menstrual cycle. On every day between days 6 and 21, women had at minimum a 10% probability of being in their fertile window. Women cannot predict a sporadic late ovulation; 4-6% of women whose cycles had not yet resumed were potentially fertile in the fifth week of their cycle.ConclusionsIn only about 30% of women is the fertile window entirely within the days of the menstrual cycle identified by clinical guidelines—that is, between days 10 and 17. Most women reach their fertile window earlier and others much later. Women should be advised that the timing of their fertile window can be highly unpredictable, even if their cycles are usually regular.