| Abstract: | B[a]P 為一種廣泛存在於環境中的PAHS類致癌物質。我們分析了B[a]P 對於H1299,H1355, H23, CH27, Calu-1, H226 及CL3 等肺癌細胞株之細胞週期影響，發現B[a]P 會非常明顯地分別造成H1355 細胞的S 期細胞週期停滯及CL3 細胞的G2/M 期細胞週期停滯。當細胞受到了傷害，卻無法進入由p53所主導G1 期的細胞週期停滯時，便累積在細胞週期的S 期，然而這些帶有受傷的細胞在細胞複製時則有可能將突變帶入子細胞中。在此，我們為證實B[a]P 造成p53 突變細胞的S 期細胞週期停滯之機制，我們利用西方點墨法分析一些細胞週期調控蛋白，如phospho-Chk1, Cdc2, Rb, p53, p21 及PCNA的表現，結果顯示以1μM B[a]P 處理細胞只造成Chk1 及p53 的磷酸化，而其他蛋白的表現則無明顯的改變；然而先前研究報告指出，Chk1 的活化會使得細胞發生S 期的細胞週期停滯。除此之外，我們也發現B[a]P 會造成ERK 及p38 的活化，而ERK 的活化及其轉位到核內將使得細胞之細胞週期由G1期進到S 期。並且p-ERK 的下游蛋白，c-Myc也會因為B[a]P 而活化。我們構築EMSA 分析H1355 細胞核內c-Myc 與E-box 的結合活性。結果顯示，B[a]P 所誘導的Chk1 磷酸化及S 期的細胞停滯，皆可以被ERK 的抑制劑(PD98059) 所抑制。根據以上結果，B[a]P 所誘導的S 期細胞週期停滯需要ERK 的活化。
PAHs, typified by the common pollutant B[a]P, are widespreaded and ubiquitous environmental pollutants with known carcinogenic properties. We have previously analyzed that B[a]P effect the cell cycle progression in lung cancer cell lines such as H1299, H1355, H23, CH27, Calu-1, H226 and CL3. B[a]P-induced cell cycle arrest in S-phase and G2/M phases of the cell cycle in H1355 and CL3 cells, respectively. When cells failed to undergo a p53-mediated cell cycle arrest in G1 phase, the cells were accumulated in the Sphase with damaged DNA. It is suggested that may lead to replication of DNA on a damaged template resulting in the enhanced frequency of mutation in the daughter cell. Some cell cycle checkpoint such as phospho-Chk1, cdc2, Rb, p53, p21 and PCNA, were analyzed using Weastern blot. The checkpoint kinase p-Chk1, p-p53 and p21 were upregulated and the other phosphorylation proteins were not changed after treatment with 1 μM of B[a]P for 24 hr. In present studies, B[a]P could also activate p38 and ERK. Activation of ERK promote the phosphorylated c-Myc to translocate into nucleus for the progression of G0/G1 to S phase. We performed an EMSA with nuclear extracts from H1355 cells could bind with E-box containing c-Myc response element. B[a]P induced activation of Chk1 and S-phase arrest were abolished by ERK specific inhibitor (PD98059) treatment. Together, these results suggest that B[a]P inducing S-phase arrest may participate in the activation of ERK. |
