Extracellular signal-regulated kinase (ERK) controls fundamental cellular functions, including cell fate decisions 1,2 . In PC12, cells shifting ERK activation from transient to sustained induces neuronal differentiation 3 . As ERK associates with both regulators and effectors 4 , we hypothesized that the mechanisms underlying the switch could be revealed by assessing the dynamic changes in ERK-interacting proteins that specifically occur under differentiation conditions. Using quantitative proteomics, we identified 284 ERK-interacting proteins. Upon induction of differentiation, 60 proteins changed their binding to ERK, including many proteins that were not known to participate in differentiation. We functionally characterized a subset, showing that they regulate the pathway at several levels and by different mechanisms, including signal duration, ERK localization, feedback, crosstalk with the Akt pathway and differential interaction and phosphorylation of transcription factors. Integrating these data with a mathematical model confirmed that ERK dynamics and differentiation are regulated by distributed control mechanisms rather than by a single master switch.

Naphthalimmide (NI) and 1,4,5,8-naphthalentetracarboxylic diimide (NDI) derivatives were synthesized and evaluated for their antiproliferative activity. NDI derivatives 1-9 were more cytotoxic than the corresponding NI derivatives 10-18. The molecular mechanisms of 1 and 2 were investigated in comparison to mitonafide. They interacted with DNA, were not topoisomerase IIalpha poisons, triggered caspase activation, caused p53 protein accumulation, and down-regulated AKT survival. Furthermore, 1 and 2 caused a decrease of ERK1/2 and, unlike mitonafide, inhibited ERKs phosphorylation.

Cholesterol esterification by acyl-CoA:cholesterol acyltransferase (ACAT) and proliferation of vascular smooth muscle cells (VSMC) are key events in vascular proliferative diseases. Here we performed experiments to ascertain the role of cholesterol ester pathway in the control of human aortic VSMC cycle progression. Results showed that serum-induced VSMC proliferation was preceded by an increased ability of the cells to esterify cholesterol as well as by an increased expression of ACAT and multidrug resistance (MDR1) mRNAs and extracellular related kinases 1/2 (ERK1/2), whereas caveolin-1 levels were markedly decreased. Cell cycle analyses performed in the presence of two inhibitors of cholesterol esterification, directly inhibiting ACAT (Sandoz 58-035) or the transport of cholesterol substrate from plasma membrane to endoplasmic reticulum (progesterone), indicate that each inhibitor suppressed the serum-induced DNA synthesis by accumulation of VSMCs in the G1 phase. The effect was associated with a rapid inhibition of ERK1/2 mitogenic signaling pathway; a down-regulation of cyclin D1, ACAT, and MDR1 mRNA; and an up-regulation of caveolin-1. These data provide a plausible link between cholesterol esterification and control of cell cycle G1/S transition, supporting the hypothesis that cholesterol esterification may accelerate the progression of human vascular proliferative diseases by modulating the rate of the VSMC proliferation.

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Abstract. Vinorelbine (VNR) is a semi-synthetic vinca alkaloid known to exert its antitumour activity by interfering with the polymerisation of tubulin. It has shown a broad spectrum of activity in some advanced carcinomas of lung, breast and ovary. This report demonstrates for the first time the antiproliferative effect of VNR and its molecular mechanism in human osteosarcoma in vitro. TP53 wild-type HOS cells and TP53 mutated MG-63 cells were chosen for this study. In each cell line, VNR caused a significant dose-and time-dependent growth inhibition and induced apoptotic death independent of TP53 status. Phosphorylation and/or alteration of Bcl-2 were not induced by VNR, thereby indicating a new pathway utilised by the drug to induce apoptosis in this tumour in vitro. VNR produced a down-regulation of cyclin D1 and an upregulation of p53 expression in TP53 wild-type HOS cells, whereas no alteration in cyclin D1 expression was evident in the TP53 negative MG-63 cells. These data suggest a new potential use for Vinorelbine as a therapeutic agent against human osteosarcoma. IntroductionOsteosarcoma (OS) is the most frequent malignant bone tumour with a peak incidence in the second and third decade of life (1). As a result of the introduction of neoadjuvant chemotherapy, an improvement in the long-term survival rate from 10% to nearly 70% has been achieved (2). At present, osteosarcoma patients receive full neoadjuvant multi-agent chemotherapy immediately after diagnosis. Initial tumour size and detectable metastases at diagnosis are prognostic factors and serve together with the response to chemotherapy as a basis for the risk adapted postoperative therapy factor (3,4). Despite the improved survival rate, drug resistance is still one of the major problems in the treatment of this cancer (5). Alterations in the TP53 gene are frequent in human osteosarcoma cells and have been associated with resistance to chemotherapy as well as with poor prognosis in this malignancy (6,7). Pompetti et al (8) correlated TP53 mutations with a lack of therapy-induced apoptosis, while studies by Goto et al (9) demonstrated an association between loss of heterozygosity at TP53 locus and chemoresistance in human osteosarcoma.Different studies indicate that cells lacking a p53 function may present a higher sensitivity to anticancer drugs that induce DNA damage and to the cytotoxic effects of antimicrotubule agents (10-12). Vinorelbine (VNR) is a semisynthetic vinca alkaloid which binds to · and ß tubulin, thus inhibiting microtubule assembly and impairing metaphasic tumour cell division. Compared with different vinca alkaloids, VNR shows markedly improved clinical efficacy and reduced toxicity (13). This drug is now widely used and licensed for the treatment of non-small cell lung cancer, breast cancer and ovarian cancer (14) and shows promise in relapsed or refractory Hodgkin's disease (15) and prostatic carcinoma (16). Like other antimicrotubule agents, VNR is known to be a promoter of apoptosis in cancer cells. The precise mechanism b...

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