The apparent protective effect of the MTHFR 1298C allele against CHD could have several explanations and further study is needed.

Mammalian topoisomerase II␣ (Topo II) is a highly regulated enzyme essential for many cellular processes including the G 2 cell cycle checkpoint. Because Topo II gene expression is regulated posttranscriptionally during the cell cycle, we investigated the possible role of the 3-untranslated region (3-UTR) in controlling Topo II mRNA accumulation. Reporter assays in stably transfected cells demonstrated that, similar to endogenous Topo II mRNA levels, the mRNA levels of reporter genes containing the Topo II 3-UTR varied during the cell cycle and were maximal in S and G 2 /M relative to G 1 . Topo II 3-UTR sequence analysis and RNA-protein binding assays identified a 177-nucleotide (base pairs 4772-4949) region containing an AUUUUUA motif sufficient for protein binding. Multiple proteins (84, 70, 44, and 37 kDa) bound this region, and the binding of 84-and 37-kDa (tentatively identified as the adenosine-or uridinerich element-binding factor AUF1) proteins was enhanced in G 1 , correlating with decreased Topo II mRNA levels. The binding activity was enhanced in cellular extracts or cells treated with thiol-reducing agents, and increased binding correlated with decreased Topo II mRNA levels. These results support the hypothesis that cell cycle-coupled Topo II gene expression is regulated by interaction of the 3-UTR with redox-sensitive protein complexes. Topo II) 1 is a multifunctional protein involved in many cellular processes including replication, repair, transcription, recombination, chromosome condensation and segregation, and the G 2 cell cycle checkpoint pathway (1-5). Topo II levels (mRNA, protein, and activity) increase in late S phase, peak in G 2 /M, and rapidly decrease following mitosis (4, 6 -8). Consistent with these observations, inhibitors of Topo II have been shown to arrest mammalian cells before mitosis in the G 2 phase of the cell cycle (6, 9 -12), and deregulated expression of Topo II results in cell death (13). In HeLa cells synchronized by mitotic shake-off, Topo II mRNA levels increased 16-fold in late S to G 2 /M phases (14 -18 h after plating) relative to G 1 (6). This increase in Topo II mRNA level was associated with a significant increase in Topo II mRNA stability, but with only marginal changes in the transcription rate. Mammalian topoisomerase II␣ (The regulation of mRNA stability has emerged as an important control mechanism of gene expression. Although the mechanisms that alter mRNA stability of different genes have unique features, in general, sequences located in the 3Ј-untranslated region (UTR) and their interactions with specific proteins regulate mRNA stability (14 -17). The most common 3Ј-UTR stability determinants are adenosine-or uridine-rich elements (AREs), which include AUUUA, AUUUUA, and AUUUUUA motifs (18 -22). Furthermore, a family of proteins, the AU-binding proteins, including AUF1 (23), Hel-N1 (24), AUH (25), HuR (26), and AUBF (27), have the capacity to bind with high affinity to mRNA containing ARE. Binding of AUbinding proteins (e.g. to AREs correlates with eit...

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This study was designed to determine whether two differently modulated radiofrequencies of the type generally used in cellular phone communications could elicit a general stress response in a biological system. The two modulations and frequencies studied were a frequency-modulated continuous wave (FMCW) with a carrier frequency of 835.62 MHz and a code division multiple-access (CDMA) modulation centered on 847.74 MHz. Changes in proto-oncogene expression, determined by measuring Fos, Jun, and Myc mRNA levels as well as by the DNA-binding activity of the AP1, AP2 and NF-kappaB transcription factors, were used as indicators of a general stress response. The effect of radiofrequency exposure on proto-oncogene expression was assessed (1) in exponentially growing C3H 10T 1/2 mouse embryo fibroblasts during their transition to plateau phase and (2) during transition of serum-deprived cells to the proliferation cycle after serum stimulation. Exposure of serum-deprived cells to 835.62 MHz FMCW or 847.74 MHz CDMA microwaves (at an average specific absorption rate, SAR, of 0.6 W/kg) did not significantly change the kinetics of proto-oncogene expression after serum stimulation. Similarly, these exposures did not affect either the Jun and Myc mRNA levels or the DNA-binding activity of AP1, AP2 and NF-kappaB in exponential cells during transit to plateau-phase growth. Therefore, these results suggest that the radiofrequency exposure is unlikely to elicit a general stress response in cells of this cell line under these conditions. However, statistically significant increases (approximately 2-fold, P = 0.001) in Fos mRNA levels were detected in exponential cells in transit to the plateau phase and in plateau-phase cells exposed to 835.62 MHz FMCW microwaves. For 847.74 MHz CDMA exposure, the increase was 1.4-fold (P = 0.04). This increase in Fos expression suggests that expression of specific genes could be affected by radiofrequency exposure.

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