latrunculin-b and Adenocarcinoma

Modified actin dynamics are a unique feature of transformed cancer cells and thereby promising targets for cancer chemotherapy. While latrunculin B (LB) and pectenotoxin-2 (PTX-2), both derived from natural sources, inhibit actin polymerization, jasplakinolide (JSP) prevents actin depolymerization. The purpose of this study was to examine the detailed molecular action of actin disruption inducing apoptosis via double strand breaks (DSBs). Actin disruption induced phosphorylation of H2AX, a well known DSB marker leading to G2 arrest and consequently resulted in apoptosis on MCF-7 cancer cells. Cells impaired by actin disruption activated Erk (extracellular signal-related kinase) and p53 protein was involved in DNA damage responses, but did not change the levels of p21Cip1/WAF1 protein in MCF-7 cells. To overcome the DSBs by actin disruption, MCF-7 cells set the repair system through the homologous recombination (HR) pathway. These results indicate that actin is involved in the signaling inducing DSBs and HR repair as well as G2 cell cycle arrest in human cancer. Therefore, the results suggest that actin disruption might be a potential candidate for developing anti-cancer therapies in human breast cancer.

Topics: Adenocarcinoma; Antineoplastic Agents; Apoptosis; Breast Neoplasms; Bridged Bicyclo Compounds, Heterocyclic; Cell Cycle; Cell Line, Tumor; Cell Proliferation; DNA Breaks, Double-Stranded; DNA Repair; Dose-Response Relationship, Drug; Female; Histones; Humans; Phosphorylation; Recombination, Genetic; Thiazolidines

The tumor suppressor p21WAF/CIP1 mediates the proliferation arrest via p53-dependent or -independent gene transactivation following distinct environmental stresses. In this study, we show that direct destabilization of the actin cytoskeleton by actin-targeting reagents leads to a p53-independent up-regulation of p21WAF/CIP1. The actin-targeting agent cytochalasin B (10 microM) quickly disrupted the actin cytoskeleton of p53 wild-type and p53-null cells accompanied by up-regulation of p21WAF/CIP1. Nevertheless, both total p53 and ser-15 phosphorylated p53 were not accumulated concomitantly, compared to the effect caused by ionizing irradiation. P53-independent up-regulation of p21WAF/CIP1 was also observed by two other actin-targeting agents cytochalasin D and latrunculin B, but not by the microtubule inhibitor colcemid. Furthermore, we showed that p21WAF/CIP1 mRNA level was not increased, whereas the protein degradation was delayed. A reduction of ubiquitination for p21WAF/CIP1 protein was detected using immunoprecipitation/immunoblot analysis. Up-regulation of p21WAF/CIP1 was not associated with cytotoxicity induced by cytochalasin B that influenced DNA integrity and plating efficiency only after 24 h of treatment. In addition, up-regulated p21WAF/CIP1 was accompanied by reduction of phosphorylation on retinoblastoma (Rb) protein in p53-null cells, implying that p21WAF/CIP1 might in part account for the molecular regulation of cytochalasin B induced G1 phase arrest. Together, current results suggest that p21WAF/CIP1 level can be mediated by actin organization in the absence of p53 via a post-transcriptional machinery, and it may contribute to the growth ablation by agents targeting the actin cytoskeleton.

Topics: Actins; Adenocarcinoma; Bone Neoplasms; Bridged Bicyclo Compounds, Heterocyclic; Carcinoma, Non-Small-Cell Lung; Cell Cycle; Cell Line, Tumor; Cyclin-Dependent Kinase Inhibitor p21; Cytochalasin D; Cytoskeleton; DNA, Neoplasm; Genes, p53; Humans; Lung Neoplasms; Osteosarcoma; RNA Processing, Post-Transcriptional; RNA, Messenger; RNA, Neoplasm; Thiazolidines; Ubiquitin