TRANSCRIPTIONAL EFFECTS IN GH(3) CELLS OF G(S)ALPHA MUTANTS ASSOCIATED WITH HUMAN PITUITARY-TUMORS - STIMULATION OF ADENOSINE-3',5'-MONOPHOSPHATE RESPONSE ELEMENT-BINDING PROTEIN-MEDIATED TRANSCRIPTION AND OF PROLACTIN AND GROWTH-HORMONE PROMOTER ACTIVITY VIA PROTEIN-KINASE-A
C. Gaiddon et al., TRANSCRIPTIONAL EFFECTS IN GH(3) CELLS OF G(S)ALPHA MUTANTS ASSOCIATED WITH HUMAN PITUITARY-TUMORS - STIMULATION OF ADENOSINE-3',5'-MONOPHOSPHATE RESPONSE ELEMENT-BINDING PROTEIN-MEDIATED TRANSCRIPTION AND OF PROLACTIN AND GROWTH-HORMONE PROMOTER ACTIVITY VIA PROTEIN-KINASE-A, Endocrinology, 136(10), 1995, pp. 4331-4338
Somatic mutations of the alpha-subunit of G(s) (G(s) alpha) have been
detected previously at high frequency in human PRL- and/or GH-producin
g pituitary tumors. To test whether these mutants are responsible for
the increased production of these hormones, we used transient cotransf
ection assays to analyze their genomic effects in GH(3) rat pituitary
cells. We first show that guanosine triphosphatase (GTPase)deficient G
(s) alpha subunits (mutated at amino acid 201 or 227) stimulate transc
ription from a reporter construct bearing the consensus cAMP response
element (CRE; TGACGTCA). Using GAL4-CRE-binding protein fusion constru
cts, we further show that this stimulatory effects of G(s) alpha on th
e CRE is probably mediated by the transacting factor CRE-binding prote
in. Then, in experiments using a reporter gene driven by the human pro
moters for either the PRL (position -250 to 18) or GH (position -500 t
o 13) genes, we show that these mutant G(s) alpha subunits stimulate e
xpression driven by either the PRL or GH promoter. Finally, we show th
at a dominant inhibitory mutant of cAMP-dependent kinase (protein kina
se A) completely blocks the ability of these G(s) alpha mutants to sti
mulate the activity of either the PRL or GH promoter, implying that GT
Pase-deficient G(s) alpha subunits stimulation of the activities of th
ese promoters is mediated entirely via the cAMP/protein protein kinase
A pathway. Taken together, these results imply that activation of thi
s pathway by the GTPase-deficient mutants found in human pituitary tum
ors stimulates the expression of PRL and GH genes. The transcriptional
effects exerted via this pathway may thus provide a basis for the sec
retory phenotype and endocrine disorders associated with these tumors.