Identification of adrenocorticotropin receptor messenger ribonucleic acid in the human pituitary and its loss of expression in pituitary adenomas.
The ACTH receptor (ACTH-R) is the second member of the melanocortin (MC-2) receptor family that includes five seven-transmembrane G protein-coupled receptors and has been shown to be predominantly expressed in the adrenal cortex. It has been postulated that ACTH may regulate its own secretion through ultra-short-loop feedback within the pituitary. ACTH-secreting adenomas are characterized by resistance to glucocorticoid feedback, and they may have dysregulated ACTH feedback. We therefore investigated the ACTH-R in normal and adenomatous human pituitary tissue. We report here the identification of ACTH-R mRNA in the human pituitary gland, which was confirmed by direct sequencing. We studied the expression of the ACTH-R in 23 normal pituitary specimens and 53 pituitary adenomas (22 ACTH-secreting, nine GH-secreting, eight prolactin-secreting, one TSH-secreting, one FSH-secreting, 10 nonfunctioning, and two silent corticotroph adenomas), using the sensitive technique of real-time quantitative PCR. Contamination of ACTH-secreting adenomas and nonfunctioning pituitary adenomas with nonadenomatous tissue was excluded by lack of Pit-1 expression. ACTH-R mRNA was detected in all normal pituitary specimens, and in situ hybridization colocalized expression to ACTH staining cells only. However, ACTH-R mRNA levels were undetectable in 16 of 22 ACTH-secreting tumors and in both silent corticotroph tumors. Diagnostic preoperative plasma ACTH levels were significantly lower in the ACTH-R positive ACTH-secreting tumors, compared with those who were ACTH-R negative (P = 0.0006). Direct sequencing of the coding region of the ACTH-R in cDNA from three ACTH-secreting tumors positively expressing the receptor showed no mutations, as did sequencing of genomic DNA in three receptor negative ACTH-secreting tumors and the two silent corticotrophs. These results provide further evidence compatible with an ACTH feedback loop in the pituitary and suggest that loss of expression of the ACTH-R in corticotroph adenomas of patients with Cushing's disease may play a role in the resistance to feedback of the pituitary-adrenal axis seen in these patients.
Morris
Damian G
DG
Department of Endocrinology, St Bartholomew's Hospital, London EC1A 7BE, United Kingdom.
Kola
Blerina
B
Borboli
Ninetta
N
Kaltsas
Gregory A
GA
Gueorguiev
Maria
M
McNicol
Anne Marie
AM
Ferrier
Roderick
R
Jones
T Hugh
TH
Baldeweg
Stephanie
S
Powell
Michael
M
Czirják
Sándor
S
Hanzély
Zoltán
Z
Johansson
Jan-Ove
JO
Korbonits
Márta
M
Grossman
Ashley B
AB
D000236:Adenoma / Q000378:metabolism*; D000293:Adolescent; D000324:Adrenocorticotropic Hormone / Q000097:blood; D000328:Adult; D000368:Aged; D002648:Child; D018076:DNA, Complementary / Q000235:genetics; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008297:Male; D008875:Middle Aged; D010902:Pituitary Gland / Q000378:metabolism*; D010911:Pituitary Neoplasms / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011333:Pro-Opiomelanocortin / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D018043:Receptors, Corticotropin / Q000235:genetics* / Q000378:metabolism; D014018:Tissue Distribution
D018076:DNA, Complementary; D012333:RNA, Messenger; D018043:Receptors, Corticotropin; D011333:Pro-Opiomelanocortin; D000324:Adrenocorticotropic Hormone