Initiation of pro-opiomelanocortin mRNA from a normally quiescent promoter in a human small cell lung cancer cell line

We describe the characteristics of pro-opiomelanocortin (POMC) mRNA synthesized by a human small cell lung cancer (SCLC) cell line that secretes a peptide immunoreactive with antibodies to the POMC-derived component, adrenocorticotropin. While no alteration in restriction endonuclease pattern or structure was found for the SCLC-derived pomc gene vs. the previously described human pomc gene cloned from a fetal liver library, Northern-blot analysis of SCLC RNA using pomc-derived probes showed a hybridizing transcript more than 300 nucleotides longer than POMC mRNA isolated from human pituitaries, as well as a pomc-gene-hybridizing mRNA the same length as pituitary-derived transcripts. 5' end mapping and primer extension analyses showed that the novel mRNA species is initiated at a site 371 bp upstream from the 5' end identified for pituitary-derived POMC mRNA. We conclude that synthesis of POMC transcripts occurs from an ordinarily quiescent promoter in the SCLC cell line we have studied, as well as from the pomc promoter normally used in pituitary cells.