Emerging evidence suggests that aberrant O-GlcNAcylation is associated with tumorigenesis. Many oncogenic factors are O-GlcNAcylated, which modulates their functions. However, it remains unclear how O-GlcNAcylation and O-GlcNAc cycling enzymes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), affect the development of cancer in animal models. In this study, we show that reduced level of OGA attenuates colorectal tumorigenesis induced by Adenomatous polyposis coli (Apc) mutation. The levels of O-GlcNAcylation and O-GlcNAc cycling enzymes were simultaneously upregulated in intestinal adenomas from mice, and in human patients. In two independent microarray data sets, the expression of OGA and OGT was significantly associated with poor cancer-specific survival of colorectal cancer (CRC) patients. In addition, OGA heterozygosity, which results in increased levels of O-GlcNAcylation, attenuated intestinal tumor formation in the Apcmin/+ background. Apcmin/+
OGA+/− mice exhibited a significantly increased survival rate compared with Apcmin/+ mice. Consistent with this, Apcmin/+
OGA+/− mice expressed lower levels of Wnt target genes than Apcmin/+. However, the knockout of OGA did not affect Wnt/β-catenin signaling. Overall, these findings suggest that OGA is crucial for tumor growth in CRC independently of Wnt/β-catenin signaling.
Communication satellites have a much longer propagation delay than terrestrial communication networks such as cellular or WiFi. In addition, as the carrier frequency moves up, mobile satellite communications show worse performances than the conventional fixed satellite communications. The mobile satellite service (MSS) has not been actively pursued with long latency at high-frequency bands for future applications. In this paper, the adverse impact of long propagation delay in the conventional satellite system is investigated with various user mobility and Doppler-shifted carrier frequency. The satellite network is modeled as a basic delayed feedback channel system and the communication performance is analyzed under delayed channel state information (CSI) for assessing the system feasibility in mobile conditions. The results of performance analysis are provided at high-frequency bands with high-speed user movement, specifically on the outage probability and the channel capacity exploiting three types of channel models: conventional land mobile satellite (LMS) channel models of E. Lutz and C. Loo, and Nakagami fading model. In the circumstance with various user speeds, system performances are evaluated with different propagation delays in the LMS channel models and for line-of-sight (LOS) components in the Nakagami fading. In addition, the conventional models are compared depending on different altitudes for geostationary orbit (GEO), medium earth orbit (MEO), and low earth orbit (LEO) satellites, as well as high-altitude platforms (HAP).INDEX TERMS Mobile satellite communications, delayed channel state information (CSI), land mobile satellite (LMS) channel model, outage probability, channel capacity.
I. INTRODUCTIONSatellites can provide global coverage and persistent communication services during emergencies when ground infrastructure systems have been damaged [1]-[3]. Satellite communication systems are one-way or two-way radio frequency (RF) transmission systems based on local oscillators in launched satellites, which operate in a wide bandwidth range of the 1-30 GHz band. These systems are essentially different from terrestrial systems in terms of the resources used, cost, transmission technologies, and in how they are deployed and operated. The satellite network consists of the space, ground and control segments, specifically satellites, ground gateways and network management stations, respectively. In general, satellite systems can be classified according to the altitude at which they are deployed and the types of The associate editor coordinating the review of this manuscript and approving it for publication was Junfeng Wang.
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