Functional analysis of the 5'-flanking region of the human gastrin-releasing peptide gene in small cell lung carcinoma cell lines.

The mammalian bombesin-like peptide, gastrin-releasing peptide (GRP), is expressed by many small cell lung carcinomas (SCLC), stimulates the growth of some SCLC and thus is an autocrine growth factor for a subset of SCLC. The subset of SCLC that expresses GRP typically shows neuroendocrine differentiation and has been designated as "classic" SCLC. To begin to characterize the mechanisms responsible for the expression of GRP in classic SCLC, the 5'-flanking region of the human GRP gene was sequenced and analyzed for cis-acting elements. Constructs containing up to 6.0 kilobases of 5'-flanking region were transiently expressed in SCLC and in control cell lines. Deletion analysis demonstrated that a sequence of 178 bases upstream of the transcriptional start was sufficient for basal expression in SCLC cell lines. A negative regulatory element was located between -5.5 and -2.6 kilobases; a general enhancer element was located between -1409 and -1197 kilobases, and a tissue-specific element was located between -1128 and -793 kilobases. Mobility shift analysis indicated that proteins from nuclear extracts of classic SCLC but not variant SCLC bound to this tissue-specific regulatory element. Thus the regulation of GRP gene expression in SCLC cell lines is a balance between a negative element, a general enhancer, and a tissue-specific element that appears active only in classic SCLC cell lines.