Nucleotide sequence analysis of c-raf-1 cDNA and promoter from a radiation-resistant human squamous carcinoma cell line: deletion within exon 17.
The c-raf-1 proto-oncogene is the cellular homologue of v-raf, the oncogene of the acutely transforming retrovirus 3611-MSV. The product of c-raf-1 (raf-1) is a 74-kDa cytoplasmic serine/threonine protein kinase. We previously reported that antisense human c-raf-1 cDNA transfection results in reduction of the endogenous c-raf-1 transcript, decreased tumor growth rate, and enhanced radiation sensitivity of SQ-20B tumor cells established from a radiation-resistant laryngeal squamous cell carcinoma. In the study reported here, we used cDNA-linked polymerase chain reaction amplification and nucleotide sequencing to examine the structure of the 3233-bp SQ-20B c-raf-1 cDNA. The 812-bp c-raf-1 promoter region was analyzed by genomic DNA amplification followed by cloning and sequencing. Sequence comparison with a previously published c-raf-1 sequence indicated no structural changes within the coding region of SQ-20B c-raf-1. However, a 4-bp deletion was observed in the 3' untranslated region within exon 17. This deletion was also present in a c-raf-1 cDNA clone isolated from a SQ-20B cDNA library. While the possibility of a 3' transcriptional control mechanism cannot be ruled out, it appears that the raf-1 protein kinase may regulate the development of radioresistant malignancies via interaction with other molecules in the damage and repair-related signal transduction pathways.
Patel
B K
BK
Department of Radiation Medicine, Lombardi Cancer Center, Georgetown University Medical School, Washington, DC 20007.
Kasid
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D001483:Base Sequence; D002294:Carcinoma, Squamous Cell / Q000235:genetics* / Q000532:radiotherapy; D004273:DNA, Neoplasm / Q000235:genetics*; D005091:Exons / Q000235:genetics*; D017353:Gene Deletion; D006258:Head and Neck Neoplasms / Q000235:genetics* / Q000532:radiotherapy; D006801:Humans; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic / Q000235:genetics*; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D019908:Proto-Oncogene Proteins c-raf; D011836:Radiation Tolerance; D014158:Transcription, Genetic / Q000235:genetics; D014407:Tumor Cells, Cultured / Q000528:radiation effects
D004273:DNA, Neoplasm; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D019908:Proto-Oncogene Proteins c-raf