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The results suggest that testosterone and DHT may have differential effects on the cross-talk between mTOR and AR. However, the increase at 5 nM testosterone appeared unrelated to a change of AR level. Rapamycin completely blocked the phosphorylation of p70S6K and S6, and decreased only marginally the phosphorylation of 4EBP-1 (Figure 4A). The next step was to address whether mTOR regulates AR in a reciprocal manner and if testosterone modulates the signal from mTOR to AR. PSA was used as a target gene of AR to assess the successful inhibition of AR activity by AR knockdown.
The LNCaP human prostate cancer cell line was obtained from the American Type Culture Collection, Manassas, VA, USA. Since testosterone is the major circulating androgen, the present study was designed to investigate the role of testosterone on the reciprocal communication between AR and mTOR. The above findings were observed in a culture condition with very low androgen levels. A recent report suggested that androgen up-regulates mTOR activity via AR-mediated transcription of nutrient transporters (5). MTORC1 supports global protein translation by phosphorylating downstream effectors, such as p70S6 kinase, S6 ribosomal protein, and 4EBP-1 (2, 3).
The deficiency of either mTOR or raptor reduces the phosphorylation of mTORC1 downstream targets, such as p70S6K1 and 4EBP1 and increases the phosphorylation of Akt at S473 and T308. To avoid the early embryonic mortality of mice deficient for mTOR and rictor/raptor, muscle-specific knockout mice of mTOR and mTOR components were generated (Guertin et al., 2006; Bentzinger et al., 2008). MTORC1 controls protein synthesis by activating S6 kinase 1 (S6K1) and inhibiting 4E-binding protein 1 (4EBP1) (Ma and Blenis, 2009). The tumor suppressor tuberous sclerosis complex TSC1-TSC2 mediates the upstream signals of mTORC1 except for amino acid availability by acting as a GTPase-activating protein (GAP) for the small GTPase Rheb. Hence, the maintenance of muscle mass has been recognized as a determinant which directly influences quality of life. MTOR inhibitor rapamycin alleviated the…
Effect of glucose deprivation on induction of cell death in high testosterone- or low testosterone-acclimated cells. The low testosterone-acclimated cells were much more resistant to apoptotic death than the high testosterone-acclimated cells (Figure 7). As noted above, the induction of AR protein by inhibition of mTOR activity is only operative in a low testosterone condition. Thus, in the face of an energy crisis when mTOR activity is greatly compromised, AR function is needed to keep cells in a survival mode. The data suggest that the growth inhibitory effect of bicalutamide may be reversible, and cells are able to recover from growth arrest over time. First, the effects of glucose deprivation, bicalutamide, or the combination treatment on cell growth were evaluated in a low testosterone condition. LNCaP cells were treated with 10 nM rapamycin in the presence of 0.03, 1 or 5 nM DHT.
Total RNA was extracted from left ventricular myocardial tissue using Trizol reagent. M-mode echocardiography recordings were obtained for the level of papillary muscle. The sign of successful model establishment was that continuous vaginal shedding cell smear examination showed the disappearance of estrous cycle changes in rats and the cell type was estrous interphase I and II. Therefore, mTOR is a crucial regulator of the maintenance of cardiac function under myocardial compensatory and pressure overload. Mammalian rapamycin receptor (mTOR) is a potentially important regulatory factor in various regulatory pathways that affect cardiac function (Huang et al. 2020, Liu & Sabatini 2020). Except for estrogen, changes in androgen levels may contribute to the occurrence of postmenopausal cardiovascular disease.
There was no difference in SBP and DBP levels between the medium-dose group and the low-dose group at the end of day 21 after intervention. The levels of IVST, LVPWT, LVM, E/A, and E/e’ in the OVX + E + T group were greater than those in the OVX + E group (Fig. 2A and Table 2). There were statistically significant differences in blood pressure at various time points after testosterone intervention, and the effect of testosterone on blood pressure remained stable (Fig. 1A and B). The testosterone level in OVX + E + T group was higher than that in other groups (Table 1). Before drug intervention, the baseline level of blood pressure levels was same in each group.
However, the testosterone sensitivity of Akt/mTOR signaling requires further understanding in order to grasp the significance of varied testosterone levels seen with wasting disease on muscle protein turnover regulation. The outcome is predictable because the low testosterone-acclimated cells are able to up-regulate AR protein and activity, and are therefore better equipped for survival in a stress situation. The data of the scrambled siRNA control cells presented in Figure 2B show that the phosphorylation of p70S6K and S6 was increased by testosterone stimulation (lane 1 vs. lane 3). These results indicated that the mTOR pathway plays a key role in testosterone-induced OVX SHR myocardial hypertrophy. Finally, the relationship between the total elevated levels of these proteins (mTOR, S6K1 and 4E-BP1) induced by testosterone and their phosphorylated form remains unclear and requires further investigation. First, this study effectively identified the mTOR signaling pathway as a potential target of testosterone-induced OVX SHR cardiac hypertrophy, but it did not explore mTOR upstream regulatory molecules.
However, the protein expression levels of S6K1 in myocardial tissue were different from the same pattern of mTOR protein expression. These studies led us to propose the hypothesis that the mTOR signaling pathway is involved in testosterone-induced elevated blood pressure and cardiac hypertrophy in postmenopausal women. Aortic constriction-induced myocardial hypertrophy is accompanied by an increase in mTOR activity (McMullen et al. 2004).
Concurrently, TSC2 dissociates from Rheb, followed by the reduction of TSC2 on the cell periphery and the subsequent increase of mTORC1 activity (Song et al., 2017). In support of this, the lysosome is shown to migrate to the cell periphery after nutrient stimulation through two kinetin proteins, K1F1Bβ and KIF2, which are essential to mTORC1 activation (Korolchuk et al., 2011). Nevertheless, the TSC complex activates the intrinsic GTPase activity of Rheb on the surface of the lysosome and localizes to the lysosome, at least partially through its association with Rheb-GDP in the absence of growth factors (Menon et al., 2014). Instead, both DAG and membrane DGK activity, which are critical for mTOR activation, were increased during mechanical stimulation. Among the several enzymes involved in PA biogenesis, PLD activity was increased by mechanical stretch and followed by mTOR activation (Hornberger et al., 2006). Then, GTP-bound Rheb activates mTORC1, resulting in phosphorylation of S6K1and 4EBP1, which promote protein synthesis by activating ribosomal protein S6 and by releasing the translation initiation factor eIF-4E, respectively.
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