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Adenosine stimulates connexin 43 expression and gap junctional communication in pituitary folliculostellate cells

B. Mary Lewis^*, Annette Pexa, Karen Francis^*, Vandana Verma, Anne M. McNicol, Maurice Scanlon^*, Andreas Deussen, W. Howard Evans, D. Aled Rees^* and Jack Ham^*,1

^* Centre for Endocrine and Diabetes Sciences,

Department of Medical Biochemistry and Immunology, School of Medicine, Cardiff University, Cardiff, UK;

Institut fuer Physiologie, Medizinische Fakultaet Carl Gustav Carus, Dresden, Germany; and

University of Glasgow, Department of Pathology, Royal Infirmary, Glasgow, UK

¹Correspondence: Centre for Endocrine and Diabetes Sciences, School of Medicine, Cardiff University, Cardiff CF14 4XN, UK. E-mail: wmdjh{at}cardiff.ac.uk

ABSTRACT

Adenosine is known to stimulate interleukin (IL)-6 and vascular endothelial growth factor (VEGF) secretion from pituitary TtT/GF folliculostellate (FS) cells indicating that it is an important paracrine regulator of anterior pituitary function. This study demonstrates that rodent anterior pituitary cell lines produce extracellular adenosine that is able to increase intercellular gap junction communication in FS cells. Ecto-5'-nucleotidase (CD73), the enzyme that generates adenosine from AMP, was demonstrated by immunocytochemistry in 20% of anterior pituitary cells, and some of these cells colocalized with prolactin and growth hormone. CD73 mRNA and protein were detected in GH3 and MMQ (somatotroph-lactotroph lineages) and TtT/GF cells, and enzyme activity was demonstrated by the conversion of exogenously added fluorescent ethenoAMP to ethenoadenosine. Adenosine production, as measured by HPLC, was detected in GH3 (1 µM/h) and MMQ (3 µM/h) but not in TtT/GF cells. Adenosine (EC₅₀: 0.5µM) and NECA (universal adenosine receptor agonist; EC₅₀ 0.1 µM) stimulated connexin 43 (Cx43) mRNA and protein expression within 1–2 h in TtT/GF cells. Adenosine and NECA also stimulated gap junctional intercellular communication (as assessed by transmission of Alexa Fluor 488) by 6- to 8-fold in comparison with untreated TtT/GF cells. In cocultures of MMQ and TtT/GF cells, Cx43 expression in TtT/GF cells increased in proportion to the number of MMQ cells plated out. These data suggest that adenosine, formed locally in the anterior pituitary gland can stimulate gap junction communication in FS cells.—Lewis, B. M., Pexa, A., Francis, K., Verma, V., McNicol, A. M., Scanlon, M., Deussen, A., Evans, W. H., Rees, D. A., Ham, J. Adenosine stimulates connexin 43 expression and gap junctional communication in pituitary FS cells.