CUHK electronic theses & dissertations collection

Additionally, we showed that SeC induced S-phase arrest in MCF-7 cells associated with a marked decrease in the protein expression of cyclin A, D1 and D3 and cyclin-dependent kinases (CDK) 4 and 6, with concomitant induction of p21waf1/Cip1, p27Kip1 and p53. Expose of MCF-7 cells to SeC resulted in delayed onset of apoptosis as evidenced by caspase activation, PARP cleavage and DNA fragmentation. SeC treatment also triggered the activation of JNK, p38 MAPK, ERK and Akt phosphorylation. Inhibitors of ERK (U0126) or Akt (LY294002), but not JNK (SP600125) and p38 MAPK (SB203580), significantly suppressed SeC-induced S-phase arrest and apoptosis in MCF-7 cells. In conclusion, our findings establish a mechanistic link between the PI3K/Akt pathway, MAPK pathway and SeC-induced cell cycle arrest and apoptosis in human breast cancer cells. (Abstract shortened by UMI.)The role of selenium as potential cancer chemopreventive and chemotherapeutic agents has been supported by epidemiological, preclinical and clinical studies. Although cell apoptosis has been evidenced as a critical mechanism mediating the anticancer activity of selenium, the underlying molecular mechanisms remain elusive. In the present study, selenocystine (SeC), a novel organic selenocompound, is identified as a novel antiproliferative agent with a broad spectrum of inhibition against eight human cancer cell lines with the IC50 values ranged from 3.6 to 37.0 muM. Despite this potency, SeC was relatively nontoxic toward HS68 human fibroblasts with an IC 50 value exceeded 400 muM. Further investigation on the molecular mechanisms indicated that SeC induced caspase-independent apoptosis in MCF-7 breast carcinoma cells, which was accompanied by poly(ADP-ribose) polymerase (PARP) cleavage, caspase activation, DNA fragmentation, phosphatidylserine exposure and nuclear condensation. Moreover, SeC induced the loss of mitochondrial membrane potential (DeltaPsim) by regulating the expression and phosphorylation of pro-surivival and pro-apoptotic Bcl-2 family members. Loss of DeltaPsim led to the mitochondrial release of cytochrome c and apoptosis-inducing factor (AIF) which subsequently translocated into the nucleus and induced chromatin condensation and DNA fragmentation. MCF-7 cells exposed to SeC shown increase in total p53 and phosphorylated p53 on serine residues of Ser15, Ser20, and Ser392 prior to mitochondrial dysfunction. Silencing and attenuation of p53 expression with RNA interference and pifithrin-alpha treatment respectively, partially suppressed SeC-induced cell apoptosis. Furthermore, generation of reactive oxygen species (ROS) and subsequent induction of DNA strand breaks were found to be upstream cellular events induced by SeC. The thiol-reducing antioxidants, N-acetylcysteine and glutathione, completely blocked the initiation and execution of cell apoptosis. Taken together, these results suggest that SeC, as a promising anticancer selenocompound, induces caspase-independent apoptosis in MCF-7 cells mediated by ROS generation and p53 phosphorylation through regulating the mitochondrial membrane permeability.Chen, Tianfeng.Adviser: Yun-Shing Wong.Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3260.Thesis (Ph.D.)--Chinese University of Hong Kong, 2008.Includes bibliographical references (leaves 124-136).Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.Abstracts in English and Chinese.School code: 1307