Chien Chung-Liang, Chen Yung-Chia, Chang Ming-Fong, Greenberg Andrew S, Wang Seu-Mei
Department of Anatomy and Cell Biology, College of Medicine, National Taiwan University, 1-1 Jen-Ai Road, Taipei, 100, Taiwan.
Histochem Cell Biol. 2005 Jun;123(4-5):429-39. doi: 10.1007/s00418-005-0771-8. Epub 2005 Apr 21.
Magnolol stimulates adrenal steroidogenesis and induces the distributional changes of p160 and adipose differentiation-related protein (ADRP) in rat adrenal cells. This study investigated the underlying signaling mechanisms involved in these processes. Magnolol (30 microM) caused a time-dependent increase in the phosphorylation of extracellular signal-related kinase (ERK) in cultured adrenal cells. The following evidence supports a link between ERK activation and p160 translocation. First, the magnolol-induced redistribution of p160 from the lipid droplet surface to the cytosol, resulting in the decrease in the percentages of p160-positive cells, and this decrease in p160-positive cells was completely blocked by pretreatment with either of the MAPK-ERK kinase (MEK) inhibitors PD98059 or U0126. Second, magnolol did not significantly decrease total p160 protein levels but caused an increase in threonine phosphorylation of p160, which reached a maximum after 5 min of magnolol treatment, and this magnolol-induced phosphorylation of p160 was prevented by pretreatment with U0126, suggesting the involvement of ERK. In addition, magnolol decreased both ADRP immunostaining intensity at the lipid droplet surface and the percentage of ADRP-positive cells. This was further confirmed biochemically by the decrease in ADRP levels in total cell homogenates and in lipid droplet fractions. Magnolol-induced decrease in ADRP staining at the lipid droplet surface was not affected by pretreatment with PD98059 or U0126, indicating that ERK signaling was not involved in this event. Furthermore, treatment with 30 microM magnolol for 6 h resulted in about 50% decrease in ADRP protein level. Therefore, decreased protein levels of p160 and ADRP at the lipid droplet surface induced by magnolol were mediated via two different mechanisms: phosphorylation of p160 and downregulation of ADRP expression, respectively.
厚朴酚刺激大鼠肾上腺细胞的肾上腺类固醇生成，并诱导p160和脂肪分化相关蛋白（ADRP）的分布变化。本研究调查了这些过程中涉及的潜在信号传导机制。厚朴酚（30微摩尔）使培养的肾上腺细胞中细胞外信号调节激酶（ERK）的磷酸化呈时间依赖性增加。以下证据支持ERK激活与p160易位之间的联系。首先，厚朴酚诱导p160从脂滴表面重新分布到细胞质中，导致p160阳性细胞百分比降低，而p160阳性细胞的这种降低被丝裂原活化蛋白激酶-ERK激酶（MEK）抑制剂PD98059或U0126预处理完全阻断。其次，厚朴酚并未显著降低p160总蛋白水平，但导致p160苏氨酸磷酸化增加，在厚朴酚处理5分钟后达到最大值，而U0126预处理可阻止厚朴酚诱导的p160磷酸化，提示ERK参与其中。此外，厚朴酚降低了脂滴表面的ADRP免疫染色强度以及ADRP阳性细胞的百分比。通过总细胞匀浆和脂滴组分中ADRP水平的降低进一步得到生化证实。厚朴酚诱导的脂滴表面ADRP染色降低不受PD98059或U0126预处理的影响，表明ERK信号传导不参与此事件。此外，用30微摩尔厚朴酚处理6小时导致ADRP蛋白水平降低约50%。因此，厚朴酚诱导的脂滴表面p160和ADRP蛋白水平降低分别通过两种不同机制介导：p160的磷酸化和ADRP表达的下调。
