Alternative splicing of MDM2 mRNA in lung carcinomas and lung cell lines.
The MDM2 gene is overexpressed in several human tumors and its product may be processed into various isoforms. Recently, alternative splicing forms of MDM2 mRNA have been detected in various types of tumors. In this study, lung tissue from human non small cell lung cancers was examined for MDM2 mRNA splicing variants by nested RT-PCR. Of the 117 lung cancer tissue samples analyzed, a total of 31 (26.5%) had splice variants for the MDM2 gene, while 59 (50.4%) had undetectable levels of MDM2 transcript. Further analysis indicated that the predominant variant for 26 of the 31 samples with alternative MDM2 splicing products was MDM2-657, a splice variant lacking exons 3-11. Significant associations were found between the frequency of alternative splicing and the gender and smoking habits of the patients. Approximately 36% of male patients had alternative splicing of MDM2 compared with only 9.5% of female patients (P = 0.008); 44.2% of the smoker patients had alternative MDM2 splice forms versus 16.2% of nonsmokers (P = 0.003). Furthermore, most normal lung cell lines examined possessed only full-length MDM2 mRNA, while among several lung cancer cell lines, only H1355 and CaLu-1 cells lacked alternatively spliced MDM2 transcripts. When H1355 cells were treated in vitro with the cigarette smoke carcinogen benzo[a]pyrene (B[a]P) or the B[a]P metabolite benzo[a]pyrene diolepoxide (BPDE), three MDM2 splicing products were detected by nested RT-PCR. Finally, with the use of several specific inhibitors, we found that BPDE-induced MDM2 mRNA alternative splicing in H1355 cells may occur through the PI3K or MAPK pathway. Overall, our results suggest that carcinogens present in cigarette smoke increase the risk of alternative MDM2 splicing, which is highly associated with lung cancer.
Weng
Mao-Wen
MW
Institute of Medical and Molecular Toxicology, Chung Shan Medical University, 110 Section 1 Chien-Kuo N. Road, Taichung 40203, Taiwan.
Lai
Ji-Ching
JC
Hsu
Chung-Ping
CP
Yu
Kuan-Ying
KY
Chen
Chih-Yi
CY
Lin
Tong-Sen
TS
Lai
Wu-Wei
WW
Lee
Huei
H
Ko
Jiunn-Liang
JL
D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide / Q000494:pharmacology; D000368:Aged; D017398:Alternative Splicing / Q000187:drug effects / Q000235:genetics*; D001564:Benzo(a)pyrene / Q000494:pharmacology; D002277:Carcinoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006801:Humans; D008168:Lung / Q000166:cytology / Q000378:metabolism* / Q000473:pathology; D008175:Lung Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D008297:Male; D008875:Middle Aged; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D051736:Proto-Oncogene Proteins c-mdm2; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction
D004791:Enzyme Inhibitors; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D001564:Benzo(a)pyrene; D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D019869:Phosphatidylinositol 3-Kinases; D020929:Mitogen-Activated Protein Kinase Kinases