重金屬鎘影響安德艾氏蚓蛋白質激酶C活性之研究

Abstract

許多研究已指出重金屬鎘會累積在生物體內並造成多種病變，因此工業上對於鎘的使用以及其對於環境污染所造成的影響受到了相當的關注。在以蚯蚓Eisenia andrei（安德艾氏蚓）為主的研究上，鎘雖已被認為與MT（metallothionein，金屬硫蛋白）之表現、不正常的移動行為、以及個體的死亡相關，然而截至目前為止並無相關研究指明鎘引起病變之機制為何。本實驗藉由測量PKC（protein kinase C，蛋白質激酶C）酵素活性以及MT之表現，以探討鎘引起相關病變之可能機制。 在酵素活性測試中，鎘離子會導致PKCα的酵素活性受到抑制。當高濃度鈣離子與鎘離子同時加入並無法抑制鎘所導致之酵素活性下降，推測此活性抑制並與PKCα結構中之鈣離子結合位無關。然而由於鋅離子本身即對PKC活性造成抑制，因此此部份的實驗並沒有辦法確實得知鎘離子所導致之活性抑制，是否是由鎘離子與鋅離子競爭PKCα之結合位相關。 除此之外，本實驗亦同時發現鎘與PKC之活化劑phorbol 12-myistate 13-acetate (PMA)可同時引起MT表現以及個體死亡。若考慮鎘會導致PKC活性下降以及MT表現，則鎘離子、PKC以及MT表現三者之間的關係將會產生矛盾。本研究推測在E. andrei中應存在兩種以上之PKC亞型參與本實驗所觀察到的現象：α-like PKC會受到鎘離子之影響而導致其酵素活性下降；而δ-like PKC將受到鎘離子的影響而誘發MT表現以及個體死亡。透過本研究可推論出蚯蚓如何感應以及反應重金屬鎘之毒害的可能機制，但仍需要後續更深入的研究以證明此假說。

Cadmium can be accumulated in organisms and cause a variety of pathological responses. The concern of using this heavy metal and its detrimental effects to public health are rising in the past decades. So far, cadmium toxicology researches done with earthworm Eisenia andrei only correlate cadmium with heavy metal-induced responses like expression of metal-inducible metallothionein (MT), abnormal locomotion and death of individuals. However, there is still no explanation of how the organisms sense and respond to cadmium. In this experiment, the protein kinase C (PKC) activities and expression of a metal-inducible MT were measured in order to find out how cadmium interferes with the function of PKC and leads to mortality and MT expression. It was found that cadmium inhibited PKCα activity in E. andrei, both in vivo and in vitro. This inhibition was not caused by the competition between calcium and cadmium. However, the change of PKCα activity caused by competition between cadmium and zinc was still remained unproved. Furthermore, cadmium-induced responses such as mortality and MT expression were found to be synergistically induced by the PKC activator phorbol 12-myistate 13-acetate (PMA). There was a confliction resulted among cadmium toxicity, PKC activity and MT expression. This confliction may be due to the existence of multiple PKC isoforms. This multiple-isoform hypothesis suggested that an α-like PKC is responsible for the cadmium-induced inhibition of PKC activity; while a δ-like PKC is responsible for the cadmium-induced mortality and expression of MT. Although more studies are required to further prove the existence and function of these putative PKC isoforms, this study still provided a hypothesis of how earthworm senses and deals with the toxicology caused by heavy metal cadmium via isoforms of PKCs.