Activation of adenylyl cyclases, regulation of insulin status, and cell survival by Gαolf in pancreatic β-cells

Abstract

Because we recently identified the Gαolf subunit in rat pancreatic β-cells, we investigated the downstream effectors and the biological functions of this G protein in HEK-293T cells and the insulin-secreting mouse βTC-3 cell line. With the use of transient transfection of HEK-293T cells with constitutively activated Gαolf (GαolfQ214L, i.e., AGαolf), together with expression vectors encoding the adenylyl cyclase (AC) isoforms (AC-I to -VIII and soluble AC), compared with cotransfections using AGαs (GαsR201C), we observed that AGαolf preferentially activates AC-I and -VIII, which are also expressed in β-cells. Stable overexpression of wild-type or AGαolf in βTC-3 cells resulted in partial attenuation of insulin secretion and biosynthesis, suggesting that chronic activation of the Gαolf-signaling pathway is associated with β-cell desensitization. In agreement, transfected βTC-3 cells present a decreased insulin content with respect to parental cells, whereas the proinsulin convertases PC-1 and PC-2 were unaffected. Furthermore, βTC-3-AGαolf cells are resistant to serum starvation-induced apoptosis. Our findings suggest that Gαolf is involved in insulin status, cell survival, and regeneration of the insulin-secreting β-cells during development and diabetes.

Involvement of cAMP signaling in elicitor‐induced phytoalexin accumulation in Cupressus lusitanica cell cultures

“…Many studies from animal and fungal cells have suggested that GTP-binding proteins in the plasma membrane may activate adenylyl cyclase, which further synthesizes cAMP and elevates cAMP concentrations in the cytosol, and then further activates ion channels (Lichter & Mills, 1997;Regnauld et al, 2002). Therefore, it is likely that GTP-binding proteins and cAMP signaling may be involved in mediating the elicitor signals to Ca 2+ .…”

“…In fungi, a cAMP signaling pathway has been found in fungus colonization on plants, including filament growth and germ tube formation (Adachi & Hamer, 1998;Kinane et al ., 2000;Thines et al ., 2000). The cAMP signaling pathways have been well studied in animals (Wand et al ., 2001;Regnauld et al ., 2002), while the occurrence and physiological function of cAMP in higher plants have been doubted for long time because of the extremely low activity of adenylyl cyclase and almost undetectable amount of cAMP in higher plants (Assmann, 1995;Bolwell, 1995;Newton et al ., 1999). With advances in analytical biochemistry, however, an increasing body of evidence has shown that cAMP does occur in higher plants (Richard et al ., 2002) and plays various roles in many cellular processes, such as pollen tube growth (Moutinho et al ., 2001), cell cycle (Ehsan et al ., 1998), stomata closure (Curvetto et al ., 1994), and defense responses to environmental stresses (Kurosaki & Nishi, 1993;Bolwell, 1999).…”

“…Previous work has shown that cholera toxin, a G-protein activator, can stimulate β -thujaplicin accumulation (Zhao & Sakai, 2003a). Because cholera toxin is also a potential activator of adenylyl cyclase in animal cells (Regnauld et al ., 2002), we investigated whether or not cAMP signaling is also involved in β -thujaplicin accumulation. Interestingly, we found that this plant cell system also employs cAMP signaling to mediate elicitor-induced β -thujaplicin accumulation, which is an additional example of the cAMP signal working in higher plants.…”

Evolving insights regarding mechanisms for the inhibition of insulin release by norepinephrine and heterotrimeric G proteins

“…Consequently, norepinephrine and other inhibitors of adenylyl cyclases that decrease cyclic AMP levels also have multiple effects on ␤-cell function. Of the nine known isoforms of the trans-membrane adenylyl cyclases (AC I-AC IX), the following have been reported present in ␤-cells: AC I and VIII (93); AC V and VI (66); AC I, VI, and VIII (14); and ACs I-IV, VI, and VIII (32). There is also a soluble adenylyl cyclase (sAC) (11).…”

G-protein αolf subunit promotes cellular invasion, survival, and neuroendocrine differentiation in digestive and urogenital epithelial cells

“…Gaolf, originally discovered in the olfactory neuroepithelium and striatum, was subsequently identi®ed in peripheral tissues, including human and rodent testis, spleen, lung, heart, pancreatic b-cells, and human insulinomas (Jones and Reed, 1989;Zigman et al, 1993;Rius et al, 1994;Astesano et al, 1999;Ferrand et al, 1999;Re gnauld et al, 2002). The Gaolf subunit has an 88% amino acid homology with Gas, as it comprises three conserved functional domains involved in guanosine triphosphate (GTP) binding anity, GTPase activity, GPCR-dependent GTP binding and GTP-induced conformational change .…”