Abstract
Folliculostellate cell gap junctions establish a network for the transmission of information within the anterior pituitary. Connexins make up gap junction channels. Changes in connexin (Cx) turnover modify gap junction-mediated intercellular communication. We have reported that cytokines and hormones influence Cx43 turnover and coupling in folliculostellate cells and in the folliculostellate cell line TtT/GF. In addition, the expression of different connexins alters intercellular communication and connexins may have functions besides cell coupling. Here we assessed the expression, turnover and subcellular localization of Cx46 and Cx50 in the anterior pituitary and TtT/GF cells. Then, we assessed the impact of various natural (lactation, annual reproductive cycle, bFGF) and pathological (autoimmune orchitis, diabetes/obesity) conditions associated with altered anterior pituitary hormone secretion on Cx46 and Cx50. Anterior pituitary Cx46 and Cx50 expression and subcellular distribution were cell-dependent. Cx46 was expressed by folliculostellate, TtT/GF and endocrine cells. In the cytoplasm, Cx46 was chiefly associated with lysosomes. Variously sized Cx46 molecules were recovered exclusively in the TtT/GF cell nuclear fraction. In the nucleus, Cx46 co-localized with Nopp-140, a nucleolar factor involved in rRNA processing. Neither cytoplasmic nor nuclear Cx46 and Cx43 co-localized. Cx50 localized to folliculostellate and TtT/GF cells, and to the walls of blood capillaries, not to endocrine cells. Cx50 was cytoplasmic and associated with the cell membrane, not nuclear. Cx50 did not co-localize with Cx46 but it co-localized in the cytoplasm and co-immunoprecipitated with Cx43. Cx46 and Cx50 responses to various physiological and pathological challenges were different, often opposite. Cx46 and Cx43 expression and phosphorylation profiles differed in the anterior pituitary, whereas Cx50 and Cx43 were similar. The data suggest that Cx46 participates to cellular growth and proliferation and that Cx50, together with Cx43, contributes to folliculostellate cell coupling.
Highlights
The folliculostellate (FS) cells together with endocrine cells constitute the anterior pituitary gland parenchyma
The results suggest that, together with Cx43, Cx50 participates in cell-to-cell communication and that Cx46 may contribute to the proliferation and growth of FS cells
Proteins from mouse lens probed with Cx46 antibodies generated an immunoreactive band around 48 kDa, that can be resolved into a kDa band and a kDa band when the proteins were allowed to migrate longer, and a 68 kDa band at times viewed as a doublet (68–71 kDa) (Fig 1A)
Summary
The folliculostellate (FS) cells together with endocrine cells constitute the anterior pituitary gland parenchyma. The FS cells control several anterior pituitary activities [1]. FS cells produce cytokines and growth factors that regulate anterior pituitary hormone secretion [2;3]. By enclosing endocrine cells in clusters, the FS cell cytoplasmic processes organize the anterior pituitary parenchyma into follicles [6,7,8]. We and others have shown that the extent of FS cell cytoplasmic processes is responsive to the hormonal milieu [8;9] and to serum-borne molecules [10] such as the basic fibroblast growth factor (bFGF) [11;12]
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