We have found that the oncogene c-myb is differentially expressed in human lung cancer cell lines and that myb-homologous RNA can be detected only in small cell lung cancer (SCLC) cell lines. Polyadenylic acid-RNA from 13 established cell lines was examined by Northern blotting for its ability to hybridize to a radiolabeled v-myb probe. A 3.5-kilobase RNA transcript homologous to v-myb is present in four of four lines of classic SCLC and in three of four SCLC variant lines but not in five of five non-small cell lung cancer lines tested. This transcript is the same size as that found in the immature myeloid cell lines KG1, but the amount of RNA is only about 10% of that in the KG1 line. A second transcript hybridizing to v-myb, 2.4 kilobases in size, is also present in the variant SCLC lines and the COLO 320 line, all of which have amplification of the c-myc gene and markedly increased c-myc messenger RNA. The presence of myb transcripts in SCLC suggests that the myb gene may have a specific role in the initiation or maintenance of an important human epithelial tumor.

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This work was supported by American Cancer Society Grant PDT-108, NIH Training Grant 5 T32 CA09072-05, and a gift from The W. W. Smith Foundation.

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