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In the present study, we aimed to elucidate the mechanism responsible for constitutive NF-kappaB DNA-binding activity in AML cells. Intervening in aberrant signaling pathway provides a rational approach for in vivo targeting of AML cells. Constitutive NF-kappaB DNA-binding activity was observed in 16 of 22 (73%) investigated AML cases and was, in general, associated with resistance to spontaneous apoptosis. Indeed, inhibition of NF-kappaB activity by the NF-kappaB inhibitor SN-50 peptide resulted in enhanced chemotherapy-induced apoptosis. In the majority of cases, constitutive NF-kappaB activity was mediated by a Ras/PI3 kinase (PI3-K)/protein kinase B (PKB)-mediated pathway. The PI3-K inhibitor Ly294002 and the Ras inhibitor L-744832 both inhibited PKB phosphorylation and NF-kappaB DNA-binding activity. The constitutive activation of Ras GTP-ase was caused by mutations in the gene encoding for N-Ras in 29% of the cases. The constitutive NF-kappaB activity could so far not be ascribed to the autocrine production of growth factors or to mutations in the Flt3 receptor, since anti-GM-CSF, -IL-1, -IL6, -TNFalpha or the tyrosine kinase inhibitor AG1296 did not affect the NF-kappaB DNA-binding activity. The present study demonstrates that Ras activation is an important pathway for triggering the NF-kappaB pathway in AML cells. [ABSTRACT FROM AUTHOR]

In the present study, we aimed to elucidate the mechanism responsible for constitutive NF-?B DNA-binding activity in AML cells. Intervening in aberrant signaling pathway provides a rational approach for in vivo targeting of AML cells. Constitutive NF-?B DNA-binding activity was observed in 16 of 22 (73%) investigated AML cases and was, in general, associated with resistance to spontaneous apoptosis. Indeed, inhibition of NF-?B activity by the NF-?B inhibitor SN-50 peptide resulted in enhanced chemotherapy-induced apoptosis. In the majority of cases, constitutive NF-?B activity was mediated by a Ras/PI3 kinase (PI3-K)/protein kinase B (PKB)-mediated pathway. The PI3-K inhibitor Ly294002 and the Ras inhibitor L-744832 both inhibited PKB phosphorylation and NF-?B DNA-binding activity. The constitutive activation of Ras GTP-ase was caused by mutations in the gene encoding for N-Ras in 29% of the cases. The constitutive NF-?B activity could so far not be ascribed to the autocrine production of growth factors or to mutations in the Flt3 receptor, since anti-GM-CSF, -IL-1, -IL6, -TNFa or the tyrosine kinase inhibitor AG1296 did not affect the NF-?B DNA-binding activity. The present study demonstrates that Ras activation is an important pathway for triggering the NF-?B pathway in AML cells.Leukemia (2004) 18, 103-112. doi:10.1038/sj.leu.2403145 [ABSTRACT FROM AUTHOR]

In the present study, we analysed the expression and localization of p21Waf1/Cip1 in normal and malignant haematopoietic cells. We demonstrate that in normal monocytic cells, protein kinase C (PKC)-induced p21 gene activation, which is nuclear factor-?B (NF-?B) independent, results in predominantly cytoplasmic localized p21 protein. In acute monocytic leukaemia (M4, M5), monocytic blasts (N=12) show constitutive cytoplasmic p21 expression in 75% of the cases, while in myeloid leukaemic blasts (N=10), low nuclear and cytoplasmic localization of p21 could be detected, which is also PKC dependent. Constitutive p21 expression in monocytic leukaemia might have important antiapoptotic functions. This is supported by the finding that in U937 cells overexpressing p21, VP16-induced apoptosis is significantly reduced (20.0±0.9 vs 55.8±3.8%, P<0.01, N=5), reflected by a reduced phosphorylation of p38 and JNK. Similarly, AML blasts with high cytoplasmic p21 were less sensitive to VP16-induced apoptosis as compared to AML cases with low or undetectable p21 expression (42.25 vs 12.3%, P<0.01). Moreover, complex formation between p21 and ASK1 could be demonstrated in AML cells, by means of coimmunoprecipitation. In summary, these results indicate that p21 has an antiapoptotic role in monocytic leukaemia, and that p21 expression is regulated in a PKC-dependent and NF-?B-independent manner.Leukemia (2003) 17, 2113-2121. doi:10.1038/sj.leu.2403106 Published online 14 August 2003 [ABSTRACT FROM AUTHOR]

The influence of the intensity of rain and the interval between application of fungicides and the onset of rain on the efficacy of maneb-fentinacetate and fluazinam against Phytophthora infestans in potato was evaluated in pot trials and field trials. In the pot trials a clear wash-off of maneb-fentinacetate was observed when simulated rain was applied 4 hours after plants had been sprayed with the fungicide. The retention of fluazinam deposits was higher and in some trials the efficacy in the bioassay was even increased by rain, probably by redistribution from the spray deposits. When 10 mm of simulated rain was applied 4-6 days after application of the fungicides, no decrease in the efficacy was observed with both fungicides. In the field trials fluazinam also showed a better retention of deposits compared with maneb-fentinacetate. [ABSTRACT FROM AUTHOR]