We previously reported that the p53 tumor suppressor protein plays an essential role in the induction of tetraploid G1 arrest in response to perturbation of the actin cytoskeleton, termed actin damage. In this study, we investigated the role of p53, ataxia telangiectasia mutated protein (ATM), and catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) in tetraploid G1 arrest induced by actin damage. Treatment with actin-damaging agents including pectenotoxin-2 (PTX-2) increases phosphorylation of Ser-15 and Ser-37 residues of p53, but not Ser-20 residue. Knockdown of ATM and DNA-PKcs do not affect p53 phosphorylation induced by actin damage. However, while ATM knockdown does not affect tetraploid G1 arrest, knockdown of DNA-PKcs not only perturbs tetraploid G1 arrest, but also results in formation of polyploidy and induction of apoptosis. These results indicate that DNA-PKcs is essential for the maintenance of actin damage induced-tetraploid G1 arrest in a p53-independent manner. Furthermore, actin damage-induced p53 expression is not observed in cells synchronized at G1/S of the cell cycle, implying that p53 induction is due to actin damage-induced tetraploidy rather than perturbation of actin cytoskeleton. Therefore, these results suggest that p53 and DNA-PKcs independently function for tetraploid G1 arrest and preventing polyploidy formation.
Actins/*metabolism ; Apoptosis ; Catalytic Domain ; Cell Cycle Proteins/genetics/*metabolism ; Cell Line ; Cell Line, Tumor ; DNA-Activated Protein Kinase/chemistry/genetics/*metabolism ; DNA-Binding Proteins/genetics/*metabolism ; Furans/pharmacology ; *G1 Phase ; Gene Knockdown Techniques ; Humans ; Phosphorylation/drug effects ; Protein-Serine-Threonine Kinases/genetics/*metabolism ; Pyrans/pharmacology ; Tumor Suppressor Protein p53/*metabolism ; Tumor Suppressor Proteins/genetics/*metabolism

OBJECTIVETo study the expression of heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNP A2/B1) in non-small cell lung cancer (NSCLC), and the interaction between hnRNP A2/B1 protein and mRNA of DNA repair enzymes O(6)-methylguanine DNA-methyltransferase (MGMT), 8-oxoguanine DNA glycosylase (OGG1), redox factor 1(Ref-1), DNA-dependent protein kinase (including DNA-PKcs and ku).

METHODSThe expression and distribution of hnRNP A2/B1 were detected by immunohistochemistry and Western blot on 50 NSCLC samples from patients who underwent resection in Zhongshan Hospital. The hnRNP A2/B1 mRNA expression was tested by real-time PCR. Co-immunoprecipitation (co-IP) combined RT-PCR was used to investigate whether hnRNP A2/B1 could be bound with the mRNA of the above mentioned 5 DNA repair enzymes in human lung cancer cell line (HTB-182). Then immunohistochemistry and real-time PCR were used to detect the expression of MGMT in the same group of patients.

RESULTSHnRNP A2/B1 protein and mRNA expressions were increased in the NSCLC tissues than that in the corresponding normal lung tissues. HnRNP A2/B1 was expressed predominantly in the nuclei of tumor cells. The positive rate and immunohistochemistry score of hnRNP A2/B1 in tumor tissue were significantly higher than that in normal tissue (P < 0.01). In stage III-IV NSCLC, hnRNP A2/B1 expression was higher than that in stage I-II. There was no significant differences of hnRNP A2/B1 expression among patients of different age, sex, histological type, and smoking history. The results of co-IP combined RT-PCR suggested that hnRNP A2/B1 is bound with MGMT mRNA, and MGMT expression is decreased in tumor tissue of NSCLC.

CONCLUSIONSThe results of this study show that hnRNP A2/B1 protein and mRNA are highly expressed in NSCLC, and hnRNP A2/B1 is bound with MGMT mRNA, which indicate that it might be one of the mechanisms of hnRNP A2/B1 participating in the pathogenesis of NSCLC.

Blotting, Western ; Carcinoma, Non-Small-Cell Lung ; genetics ; DNA-Activated Protein Kinase ; metabolism ; Guanine ; analogs & derivatives ; Heterogeneous-Nuclear Ribonucleoprotein Group A-B ; genetics ; metabolism ; Humans ; Immunohistochemistry ; Immunoprecipitation ; Lung ; chemistry ; Lung Neoplasms ; genetics ; RNA, Messenger ; analysis ; Real-Time Polymerase Chain Reaction ; Reverse Transcriptase Polymerase Chain Reaction