Visit our Expo - Redox and Inflammation signaling 2012

Session II : Receptor signaling and G proteins Poster II, 43
Conditionnal expression of wild type or mutated Gsalphalpha induced MAPKinases
ERK-1/2, prolactin and growth hormone promoters activation in a somato-lactotroph
cell line.
David Romano, Morgane Pertuit, Karine Magalon, Anne Barlier, Ramahefarizo
Rasolonjanahary, Alain Enjalbert et Corinne Gérard.
Interactions Cellulaires Neuroendocriniennes, IFR Jean Roche, Faculté de Médecine
Nord, 13916 Marseille cedex 20, France. E-mail : romano.d@nord.univ-mrs.fr
Mutations of the Gsalphalpha (Gsa) protein, named gsp oncogene, are present in 40% of
human somatotroph adenomas. These mutations induced a constitutive activation of the Gsa
protein and an increase of adenylyl cyclase (AC) activity. However its role in tumorigenesis is
not clear because of an overlap of clinical phenotype (hormonal hypersecretion, proliferation)
between tumors bearing or not the gsp oncogene. This overlap might be due to an
overexpression of the wild type (wt) Gsa protein, mimicking the activating mutation, or to the
compensatory mechanisms like the increase of phosphodiesterase activity. To understand the
molecular mechanisms induced by the gsp oncogene, as well as the putative role of
overexpressed wt Gsa, a somato-lactotroph cell line (GH4C1) was stably transfected with wt
Gsalpha or constitutively activated Gsalpha by the R201C mutation, under the control of the
tetracycline operon (GH4C1 Tet-off).
After induction, we observe a similar increase of both wild type (wt) and mutated transgene
mRNA levels. Moreover, the time course of both transgene proteins expression follows their
mRNA synthesis with a maximum after 7 days of induction. However, the wt transgene
protein is more expressed than the mutated one, suggesting a negative post-transcriptionnal
regulation of the gsp oncogene. At a functional level, cAMP level and AC activity are
strongly increased after induction of the mutated protein, with a time course pattern similar to
the expression of the gsp oncogene. However, (i) basal MAPKinases ERK-1/2
phosphorylation, (ii) human prolactin (PRL) and growth hormone (GH) promoters activity are
progressively and similarly increased by induction of both wt and mutated Gsa proteins.
Moreover, using the MAPKinase specific inhibitor U0126, we show that this increase in both
PRL and GH promoters activity is MAPKinase-dependent.
So far, these cell lines seem to be interesting models to study the molecular mechanisms
involved in the tumorigenesis of human somatotroph adenomas bearing or not the gsp
oncogene.
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