STAU1 exhibits a dual function by promoting amyloidogenesis and tau phosphorylation in cultured cells.

Staufen-1 (STAU1) is a double-stranded RNA-binding protein (RBP) involved in a variety of pathological conditions. In this study, we investigated the potential role of STAU1 in Alzheimer's disease (AD), in which two hallmarks are well-established as cerebral ß-amyloid protein (Aß) deposition and Tau-centered neurofibrillary tangles. We found that STAU1 protein level was significantly increased in cells that stably express full-length APP and the brain of APP/PS1 mice, an animal model of AD. STAU1 knockdown, as opposed to overexpression, significantly decreased the protein levels of ß-amyloid converting enzyme 1 (BACE1) and Aß. We further found that STAU1 extended the half-life of the BACE1 mRNA through binding to the 3' untranslated region (3'UTR). Transcriptome analysis revealed that STAU1 enhanced the expression of growth arrest and DNA damage 45 ß (GADD45B) upstream of P38 MAPK signaling, which contributed to STAU1-induced regulation of Tau phosphorylation at Ser396 and Thr181. Together, STAU1 promoted amyloidogenesis by inhibiting BACE1 mRNA decay, and augmented Tau phosphorylation through activating GADD45B in relation to P38 MAPK. Targeting STAU1 that acts on both amyloidogenesis and tauopathy may serve as an optimistic approach for AD treatment.

Short-term regulation of TSFM level does not alter amyloidogenesis and mitochondrial function in type-specific cells.

BACKGROUND: Mitochondrial Ts translation elongation factor (TSFM) is an enzyme that catalyzes exchange of guanine nucleotides. By forming a complex with mitochondrial Tu translation elongation factor (TUFM), TSFM participates in mitochondrial protein translation. We have previously reported that TUFM regulates translation of beta-site APP cleaving enzyme 1 (BACE1) via ROS (reactive oxygen species)-dependent mechanism, suggesting a potential role in amyloid precursor protein (APP) processing associated with Alzheimer's disease (AD), which led to the speculation that TSFM may regulate APP processing in a similar way to TUFM. METHODS AND RESULTS: Here, we report that in cultured cells, knockdown or overexpression TSFM did not change protein levels in BACE1 and APP. Besides, the levels of cytoplasmic ROS and mitochondrial superoxide, in addition to ATP level, cell viability and mitochondrial membrane potential were not significantly altered by TSFM knockdown in the short term. Further transcriptome analysis revealed that expression of majority of mitochondrial genes were not remarkably changed by TSFM silencing. The possibility of TSFM involved in cardiomyopathy and cancer development was uncovered using bioinformatics analysis. CONCLUSIONS: Collectively, short-term regulation of TSFM level in cultured cells does not cause a significant change in proteins involved in APP processing, levels in ROS and ATP associated with mitochondrial function. Whereas our study could contribute to comprehend certain clinical features of TSFM mutations, the roles of TSFM in cardiomyopathy and cancer development might deserve further investigation.

[Mechanism of cleft palate in mice induced by 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin].

OBJECTIVE: To explore the mechanism of cleft palate in mice induced by 2, 3, 7, 8-Tetrachlorodibenzo-p-dioxin (TCDD). METHODS: On gestation day 10 (GD 10), 12 pregnant mice were randomly divided into two groups as the treated group and the control group with 6 mice in each group. The mice in the treated group received intragastric administration with 64 microg TCDD/kg, while the mice in the control group received equivalent corn oil. The embryos were examined under stereomicroscope to detect the incidence of cleft palate on GD 18.5. Another 18 pregnant mice were randomly divided into two groups (treated group and control group) on GD 10 with 9 pregnant mice in each group. Then each group was divided into 3 subgroups: GD 13.5, GD 14.5 and GD 15.5, with 3 pregnant mice in each subgroup. The palatal shelves were dissected from the embryos for RNA and DNA extraction on GD 13.5, GD 14.5 and GD 15.5. At last the expression of Smad 2-4 and Smad 7 mRNA was investigated by RT-PCR, and the TGF-beta3 promoter methylamine levels were investigated by methylation specific PCR (MSP). RESULTS: The cleft palate mice model was established successfully by exposing pregnant C57BL/6J mice to TCDD. Total frequency of clefts was 100% in TCDD group, and the frequency of clefts was 0 in the control group. The relative expression of Smad 2 mRNA was 0.263 +/- 0.088, 0.296 +/- 0.016 and 0.159 +/- 0.027 in TCDD group, 0.180 +/- 0.042, 0.282 +/- 0.029 and 0.165 +/- 0.018 in control group. The relative expression of Smad 3 mRNA was 0.453 +/- 0.153, 0.551 +/- 0.160 and 0.328 +/- 0.049 in TCDD group, 0.375 +/- 0.126, 0.510 +/- 0.145 and 0.259 +/- 0.035 in control group. The relative expression of Smad 4 mRNA was 0.675 +/- 0.174, 0.577 +/- 0.070 and 0.396 +/- 0.066 in TCDD group, 0.557 +/- 0.138, 0.587 +/- 0.080 and 0.441 +/- 0.054 in control group. The relative expression of Smad 7 mRNA was 0.283 +/- 0.050, 0.320 +/- 0.068 and 0.169 +/- 0.045 in TCDD group, 0.207 +/- 0.043, 0.288 +/- 0.051 and 0.155 +/- 0.040 in control group. There was no significant difference between the TCDD treated mice and the control (P > 0.05). The TGF-beta3 promoters were at the un-methylation state both in the TCDD treated and control group. CONCLUSION: It suggests that TCDD could induce a stable formation of cleft palate, but it is not through the TGF-beta/Smad signaling nor through the modification of TGF-beta3 promoter methylation.