Adenovirus vectors differentially modulate proliferation of pituitary lactotrophs in primary culture in a mitogen and infection time-dependent manner.

Adenoviruses are powerful, widely utilized vectors for gene transfer. Limitations to their application, however, have not beenwelldescribed.Weusedratpituitarylactotrophsinprimary cultureasamodelforstudyinghowadenovirusvector infection modulates mitogen-induced proliferation and the activities of mitogen signaling pathways. Infection with adenovirus vectors expressing b-galactosidase (bgal) raised basal proliferative levels and blocked fetal bovine serum (FBS)-induced proliferation of lactotrophs, but did not influence the changes in proliferation induced by forskolin, IGF-I, and bromocriptine. The bgalexpressing adenoviruses did not alter the inhibitory action of 17b-estradiol (E2) in the presence of IGF-I; however, they blockedthe stimulatoryactionofE2inthe presence ofdextrancoated charcoal-striped serum or forskolin. An adenovirus expressingnoproteinfailedtoblockFBS-inducedproliferation, but was effective in modulating basal proliferative levels and the stimulatory actions of E2. The increased basal proliferative level and the blockade of FBS-induced proliferation were transient, and lost 5 days after infection while the blockade of the stimulatory action of E2 in the presence of forskolin persisted. Adenovirus infection raised basal protein levels of the phosphorylated forms of cAMP response element-binding protein(pCREB)andERK1/2andincreasedtheproportionof pCREB-immunoreactive lactotrophs. Adenoviruses also altered estrogen-induced responses in mRNA expression of several estrogen-responsive genes in a gene-specific manner. The results demonstrate that an adenovirus vector differentially interferes with lactotroph proliferation in response to various mitogens. Our results suggest that the effects of the adenovirus thatareindependentofthegenestransferredmustbeconsidered