The TPIT gene mutation M86R associated with isolated adrenocorticotropin deficiency interferes with protein: protein interactions.
BACKGROUND
Tpit is a T-box transcription factor important for terminal differentiation of pituitary proopiomelanocortin-expressing cells. We previously showed that human and murine mutations in the gene encoding this highly cortico/melanotrope-specific transcription factor cause a neonatal onset form of congenital isolated ACTH deficiency (IAD). We characterized the largest series of neonatal IAD patients caused by TPIT mutations, and this revealed a highly homogeneous clinical presentation. So far, 12 different loss-of-function TPIT mutations have been identified. The methionine 86 arginine (M86R) TPIT mutation was recently identified in compound heterozygosity with the 782delA frame-shift mutation in two siblings with early-onset IAD.


OBJECTIVE
We conducted a functional analysis of the missense M86R mutation to assess transcriptional activity, DNA binding activity, and nuclear location, as well as protein-protein interactions.


RESULTS
Although the M86 residue is located within the T-box DNA-binding domain, it did not affect monomer DNA-binding activity per se, but it impaired DNA binding with other DNA-bound proteins, including itself (homodimers) and pituitary homeobox 1 (Pitx1). The M86 residue is at the interface between T domains in the T dimers crystal structure, and it appears that the same residue is involved in heterodimer formation with pituitary Pitx1. Furthermore, TPIT M86R is deficient in the recruitment of the coactivator SRC2 that partly mediates the CRH stimulation of proopiomelanocortin transcription.


CONCLUSIONS
Thus, the M86R TPIT mutation is defining an important surface of the T domain for multiple protein interactions and for transcription.
Vallette-Kasic
Sophie
S
Laboratoire de génétique moléculaire, Institut de recherches cliniques de Montréal, 110, avenue des Pins Ouest, Montréal, QC, Canada H2W 1R7.
Couture
Catherine
C
Balsalobre
Aurelio
A
Gauthier
Yves
Y
Metherell
Louise
L
Dattani
Mehul
M
Drouin
Jacques
J
D000324:Adrenocorticotropic Hormone / Q000172:deficiency*; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D004247:DNA / Q000378:metabolism; D019281:Dimerization; D016368:Frameshift Mutation; D018398:Homeodomain Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D007018:Hypopituitarism / Q000235:genetics* / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D051761:Paired Box Transcription Factors / Q000378:metabolism; D011333:Pro-Opiomelanocortin / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000502:physiology; D017434:Protein Structure, Tertiary; D020825:T-Box Domain Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology; D014162:Transfection
D018398:Homeodomain Proteins; D051761:Paired Box Transcription Factors; D020825:T-Box Domain Proteins; C486589:TBX19 protein, human; C424031:Tbx19 protein, mouse; C101485:homeobox protein PITX1; D011333:Pro-Opiomelanocortin; D000324:Adrenocorticotropic Hormone; D004247:DNA