Figure 1.

Human proopiomelanocortin (hPOMC) transcription start sites in pituitary and ectopic adrenocorticotropin (ACTH)-secreting tumors and cell lines. A, 5′-rapid amplification of complementary DNA ends (5′-RACE) analysis of human POMC messenger RNA (mRNA) isolated from human pituitary corticotroph adenomas (Cushing) and ectopic Cushing tumors (ectopic Cushing) resected from thymus, lung, and liver (see Table 1), as well as ACTH-secreting DMS79 (3 independent experiments: ex. 1, ex. 2, ex. 3) and COLO320 cells (2 independent experiments: ex. 1, ex. 2). The number of identified 5′-ends of POMC mRNA located in regions A, B, and C (depicted in B) are noted, with the number of major 5′ ends in region A located approximately 30 bp downstream of the TATA box sequence shown in parentheses. B, Number of 5′-ends of POMC mRNA in pituitary ACTH-secreting (Cushing), ectopic ACTH-secreting tumors (ectopic Cushing), and DMS79 and COLO320 cells in each region. Top, relative position of each region, with the major mRNA start site defined as position +1; relative positions of exon 1, exon 2, and exon 3 are depicted in boxes. Left scale, number of 5′ ends located in region A; right scale, number of 5′ ends located in region B and region C. C, DNA sequence in region C. Identified 5′ ends of POMC mRNA are shown in bold and flagged with an asterisk. The intron 2 sequence is shown in lowercase letters and exon 3 sequence in capital letters. Arrow indicates 5′-end of exon 3. Potential STAT and CREB binding sequences are shown in italics and underlined. Dinucleotide 5′-CG-3′ (CpG) sequences identified as potential methylation sites are underlined. The ACTH coding sequence is also underlined.