G _sα -selective G protein antagonists

Abstract

Suramin acts as a G protein inhibitor because it inhibits the rate-limiting step in activation of the G ␣ subunit, i.e., the exchange of GDP for GTP. Here, we have searched for analogues that are selective for G s␣ In current pharmacotherapy the input into G proteinregulated signaling is manipulated by targeting the receptor with appropriate agonists and antagonists. Several arguments, however, suggest that elements of the receptor-activated, downstream signaling cascade, in particular G proteins, may be considered as drug targets per se. (i) The molecular diversity of G protein ␣, ␤, and ␥ subunits is large, and the number of distinct ␣␤␥ oligomers that can be produced by combinatorial association of subunit is excessive (1). (ii) The interaction of a given receptor with the cellular complement of G proteins may be governed by both exquisite specificity and promiscuity; in the first case, only one defined oligomer supports the ability of a receptor to regulate an effector in an intact cell (for review see refs. 2 and 3). (iii) On the other hand, many receptors couple to multiple G proteins (2, 3); this is exemplified by the thyrotropin receptor (4), which can activate essentially all G protein ␣ subunits expressed in the thyroid (i.e., members of all subfamilies of G ␣ other than the transducins). Thus, cellular stimulation by a receptor often results in the concerted activation of several distinct G proteins such that multiple effector pathways are recruited to produce the biological response. In theory, it may be desirable to block signaling of a receptor via one type of G protein but not via the other G proteins (resulting in ''biased inhibition of receptor/G protein tandem formation''), a goal that cannot be achieved by receptor antagonists but that may be achieved by compounds that bind selectively to individual G proteins. In addition, several human diseases arise from activation of G protein ␣ subunits by point mutations (for a brief overview, see ref. 5); appropriate G protein antagonists are desirable under these circumstances.Suramin has been shown previously to act directly on G protein ␣ subunits (6) and to block their activation by receptors (7-9). In the present work, we have searched for compounds that inhibit G s␣ directly. Two compounds of remarkable selectivity were identified that suppress the coupling of ␤-ad-

Tricyclic Antidepressant Amitriptyline-induced Glial Cell Line-derived Neurotrophic Factor Production Involves Pertussis Toxin-sensitive Gαi/o Activation in Astroglial Cells

“…The concentrations of the selective inhibitors for the various intracellular signal cascade molecules were based on previous reports for cell culture systems (23-26, 30, 31, 38, 39). Based on the IC 50 value of these inhibitors, these inhibitors are in fact selective for their respective targets (30,(42)(43)(44)(45)(46)(47). Although 25 M GM6001 was used, which is 1000-fold of the IC 50 , a previous study used the negative analog of GM6001 to confirm selectivity of GM6001.…”

Obestatin Promotes Survival of Pancreatic β-Cells and Human Islets and Induces Expression of Genes Involved in the Regulation of β-Cell Mass and Function

“…3F). NF449, a specific antagonist of the G␣ s protein (33), whose engagement results in adenylyl cyclase activation and cAMP production (34), blocked obestatin antiapoptotic effect in serum-starved and cytokine-treated cells. Similar results were obtained by inhibiting adenylyl cyclase and protein kinase A (PKA) with MDL12330A and KT5720, respectively (20) (Fig.…”

A mechanism of cell death involving an adenylyl cyclase/PKA signaling pathway is induced by the Cry1Ab toxin of Bacillus thuringiensis

“…Membranebound ACs are activated by G ␣s (31). To ascertain whether G protein activity is involved in the Cry toxin-induced pathway, we used a cell-permeable inhibitor, NF449 (35), which selectively antagonizes G ␣s . S5 cells preincubated (30 min) with NF449 (1 M) were less sensitive to the Cry1Ab toxin than untreated cells (Fig.…”