| Abstract: | Lipopolysaccharides (LPS；內毒素)為格蘭氏陰性菌細胞壁中的成份之一。當人體免疫力下降或手術未癒之病人受到格蘭氏陰性菌嚴重感染時，細菌的LPS會經由血液侵犯人體，引發發燒、敗血性休克，甚至是器官衰竭等症狀。由於腸道組織為格蘭氏陰性菌的大本營，因此我們想探討LPS對其可能產生的生理反應。在我們的研究中，我們發現10 μg/ml LPS會刺激大腸癌上皮細胞 (Caco-2)的生長速率與移動能力。進一步探討其分子機轉，我們觀察到LPS會增加c-Src蛋白表現，進而使其下游蛋白，Shc與Erk的tyrosyl phosphorylation增加，促進細胞生長。此外，另一個Src的受質，FAK，其tyrosyl phosphorylation也因LPS促進Src整體活性提高而增加，而這可能與細胞的移動有關。RT-PCR的實驗結果指出，LPS促進c-Src蛋白量的增加與其mRNA的增加有關。
薑黃素 (curcumin)是一種薑科植物Curcuma longa地下莖，所萃取出來的黃色色素，具有抗發炎、抗氧化，以及抗癌的效果。由於其為食用色素，我們想了解其能否抑制大腸直腸癌並探討其分子機轉。因此，我們選用了一株大腸癌細胞 (Caco-2)，做為實驗材料。從我們的實驗結果，我們發現curcumin會抑制癌細胞的生長；同時我們也觀察到一個有趣的現象，那就是curcumin會減弱癌細胞metastasis的能力。當Caco-2細胞以不同濃度的curcumin處理時，細胞總體蛋白的酪胺酸磷酸化程度會明顯下降。而此與c-Src蛋白表現隨著curcumin濃度的增加而遞減相關。另外讓我們感到有趣的是，FAK，一個在integrin signaling pathway上重要的調節蛋白，它的autophosphorylation state竟也會隨著curcumin濃度的增加而下降。綜合以上的結果，我們推測curcumin造成c-Src蛋白表現與活性降低以及FAK蛋白的活性下降，或許與其抗癌與減緩癌細胞轉移的能力有關。
Lipopolysaccharides (LPS；endotoxin) are cell wall components of most gram-negative bacteria. During sereve bacterial infections, as occurred in post-operation or immune suppressed patients, large amounts of LPS may be released into the blood stream and leads to various pathophysiological reactions such as fever, septic shock, and multi-organ failure. Since GI tract is the tissue that exposed to LPS most, we are interested to study its effect on colon epithelial cells. In the study, we observed that 10 μg/ml LPS can enhance the growth rate of Caco-2 cells (colorectal adeno- carcinoma cells), and improve their metastatic ability to migrate on dish coated with collagen. Furthermore, we found that LPS could upregulate the expression of c-Src protein that in turn caused the enhancement of tyrosyl phosphorylation of Shc and ERK and promoted cellular growth. In addition, LPS induced FAK Tyr-397 phosphorylation might attribute to cell mobility.
Curcumin, an active yellow pigment of Curcuma longa, possesses anti-inflammatory, antioxidative and anticarcinogenic properties. To delineate its antitumorigenic mechanisms, the colorectal adenocarcinoma cell line, Caco-2, was utilized as the material in our study. Like what has been described in other cells, significant growth inhibition of Caco-2 was detected in the presence of curcumin. At the same time, we also found that curcumin could reduce the metastasis ability of Caco-2 cells. And when the profile of tyrosyl phosphorylated proteins was analyzed, significant reduction of overall tyrosyl phosphorylation was observed in curcumin -treated cells as compared to that in control. Surprisingly, suppression of c-Src expression in response to curcumin was observed while no change of the expression level of actin was detected. The curcumin-mediated reduction of c-Src expression resulted in the aborgation of c-Src activity as evidenced by reduced tyrosyl phosphorylation of cortactin, a Src substrate. Interestingly, accompanying with downregulation of c-Src in curcumin-treated cells was the reduced tyrosyl phosphorylation and the enzymatic activity of FAK, an important player in integrin signaling. With these findings, we suggested that curcumin-mediated reduction of the expression and activity of c-Src might attribute to curcumin-mediated anticarcinogenic effects. |
