Sirikantaramas Supaart, Sudo Hiroshi, Asano Takashi, Yamazaki Mami, Saito Kazuki
Graduate School of Pharmaceutical Sciences, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan.
Phytochemistry. 2007 Nov-Dec;68(22-24):2881-6. doi: 10.1016/j.phytochem.2007.08.028. Epub 2007 Oct 29.
We have investigated the subcellular accumulation and transport of camptothecin (CPT), a monoterpene indole alkaloid, in hairy roots of Ophiorrhiza pumila. This hairy root produces high amounts of CPT and excretes it into the culture medium. When the hairy roots were exposed to UV radiation, autofluorescence emitted from CPT showed subcellular localization of CPT in the vacuole. Treatment with several inhibitors suggested that CPT excretion is a transporter-independent passive transport controlled by the concentration gradient of the compound. Interestingly, the hairy roots treated with brefeldin A, a vesicle transport inhibitor, showed increased CPT excretion. This could be explained by an increased transport rate of CPT from the endoplasmic reticulum (ER) to the cytoplasm when transport of CPT to the vacuole is blocked. The much higher concentration of CPT in the cytoplasm resulted in the increased excretion rate. This result indicates that CPT is biosynthesized at the ER and transported to accumulate in the vacuole by the same machinery that is used for vacuolar protein sorting. How O. pumila is insensitive to CPT is discussed.
我们研究了喜树碱(CPT),一种单萜吲哚生物碱,在矮蛇根草毛状根中的亚细胞积累和转运。这种毛状根产生大量的CPT并将其分泌到培养基中。当毛状根暴露于紫外线辐射时,CPT发出的自发荧光显示CPT在液泡中的亚细胞定位。用几种抑制剂处理表明,CPT的排泄是一种不依赖转运蛋白的被动转运,受该化合物浓度梯度的控制。有趣的是,用囊泡运输抑制剂布雷菲德菌素A处理的毛状根显示CPT排泄增加。当CPT向液泡的运输受阻时,CPT从内质网(ER)到细胞质的运输速率增加可以解释这一现象。细胞质中CPT浓度的大幅提高导致排泄率增加。这一结果表明,CPT在内质网中生物合成,并通过用于液泡蛋白分选的相同机制运输到液泡中积累。文中还讨论了矮蛇根草对CPT不敏感的原因。