Ectopic Hormone Production Viewed as an Abnormality in Regulation of Gene Expression

Abstract

Publisher Summary This chapter summarizes some aspects of recent developments made in the study of ectopic hormone-producing tumors, based mainly on the results obtained from the studies of adrenocorticotropic hormone-lipotropin (ACTH-LPH)-producing tumors. Ectopic hormone production is the phenomenon by which certain neoplasms produce hormones not usually produced by tissues from which the neoplasms have arisen. Ectopic ACTH-producing tumors always elaborate β-LPH, γ-LPH, β-endorphin, and γ-MSH. All these peptides are known to be derived from a common precursor by sequential enzymatic cleavages, as has been clarified in the pituitary gland. Detailed studies comparing ectopic and pituitary hormones have shown differences only in posttranslational processing and no evidence has so far been obtained to suggest abnormalities in structural genes. These results indicate that ectopic hormone production may be caused by abnormalities in regulating gene expression. The production of multiple hormones in tumors and expressions of ectopic hormone receptors along with ectopic hormone production may indicate that the activation of either repressed or rarely transcribed unrepressed genes takes place in a relatively wide range on genomes. Because ectopic hormone production is a universal concomitant of neoplasms, abnormalities in regulating gene expression seem to be a characteristic feature of neoplasia. However, the possibility of abnormalities in regulatory genes cannot be ruled out because the deletions of some DNA sequences surrounding the structural genes of hemoglobin are reported to affect gene expression.