Gadd45β is a pro-survival factor associated with stress-resistant tumors.

Tumors that acquire resistance against death stimuli constitute a severe problem in the context of cancer therapy. To determine genetic alterations that favor the development of stress-resistant tumors in vivo, we took advantage of polyclonal tumors generated after retroviral infection of newborn Elambda-MYC mice, in which the retroviral integration acts as a mutagen to enhance tumor progression. Tumor cells were cultivated ex vivo and exposed to gamma-irradiation prior to their transplantation into syngenic recipients, thereby providing a strong selective pressure for pro-survival mutations. Secondary tumors developing from stress-resistant tumor stem cells were analysed for retroviral integration sites to reveal candidate genes whose dysregulation confer survival. In addition to the gene encoding the antiapoptotic Bcl-x(L) protein, we identified the gadd45b locus to be a novel common integration site in these tumors, leading to enhanced expression. In accord with a thus far undocumented role of Gadd45beta in tumorigenesis, we showed that NIH3T3 cells overexpressing Gadd45beta form tumors in NOD/SCID mice. Interestingly and differently to other known 'classical' antiapoptotic factors, high Gadd45beta levels did not protect against MYC-, UV- or gamma-irradiation-induced apoptosis, but conferred a strong and specific survival advantage to serum withdrawal

Collusion Theory: Where to Go Next?

This note comments on Feuerstein's (Feuerstein, Switgard, “Collusion in industrial economics: A survey,” forthcoming in Journal of Industry, Competition and Trade, 2005) survey of collusion theory. I start by presenting evidence from a recent real-world collusion case: the lysine industry. Based on this, I point out a few areas where collusion theory can improve: (a) the problem of equilibrium choice (bargaining over each firm's share), which is especially important in asymmetric oligopolies; (b) the problem of equilibrium implementation, including in particular communication in an asymmetric information context; and (c) the relation between price wars and collusion. I conclude with a few notes on policy issues, namely leniency programs and cartel detection strategies. Copyright Springer Science + Business Media, Inc. 2005collusion, cartels, public policy,