Biochemical requirements for suppressing a constitutively active allele of Gs alpha

In F9 teratocarcinoma stem cells, retinoic acid induces a primitive endoderm-like phenotype and a sharp decline in G alpha i-2, a response mimicked by expression of RNA antisense to G alpha i-2 in the absence of this morphogen (D. C. Watkins, G. L. Johnson, and C. C. Malbon. Science Wash. DC 258: 1373-1375, 1992). The role of the GS alpha/G alpha i-2 axis in cellular differentiation was explored. In the absence of retinoic acid, F9 stem cells stably expressing a constitutively active mutant of GS alpha (G225T) progressed to the primitive endoderm phenotype, as judged by morphological and differentiation markers, such as tissue plasminogen activator. Although elevated in cells expressing G225T GS alpha, adenosine 3',5'-cyclic monophosphate does not mimic retinoic acid action and alone fails to induce stem cells to primitive endoderm. In the absence of retinoic acid, expression of a null mutant of G alpha i-2 (G203T) also induced stem cells to primitive endoderm. These observations establish G proteins in the GS alpha/G alpha i-2 axis as a control point for regulating progression to primitive endoderm independent of adenylate cyclase, in the present study's model of early mouse development.

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Activation of cyclic nucleotide phosphodiesterases in FRTL-5 thyroid cells expressing a constitutively active Gs alpha

Molecular Endocrinology ◽

10.1210/me.9.10.1279 ◽

1995 ◽

Vol 9 (10) ◽

pp. 1279-1287 ◽

Cited By ~ 11

Author(s):

G. Nemoz

Keyword(s):

Cyclic Nucleotide ◽

Thyroid Cells ◽

Cyclic Nucleotide Phosphodiesterases ◽

Gs Alpha ◽

Constitutively Active ◽

Nucleotide Phosphodiesterases

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Increased expression of Gi alpha 2 in mouse embryo stem cells promotes terminal differentiation to adipocytes

AJP Cell Physiology ◽

10.1152/ajpcell.1993.265.6.c1729 ◽

1993 ◽

Vol 265 (6) ◽

pp. C1729-C1735 ◽

Cited By ~ 28

Author(s):

H. L. Su ◽

C. C. Malbon ◽

H. Y. Wang

Keyword(s):

G Protein ◽

Mouse Embryo ◽

Terminal Differentiation ◽

Wild Type ◽

Biological Responses ◽

Steady State Levels ◽

G Protein Alpha Subunit ◽

Gs Alpha ◽

Constitutively Active

The level of Gs alpha activity has been shown to modulate the rate of adipogenesis in mouse embryo fibroblast 3T3-L1 cells (H.-Y. Wang, D. C. Watkins, and C. C. Malbon. Nature Lond. 358: 334-337, 1992). For the current work the role of Gi alpha 2, a G protein mediator of inhibitory control of adenylyl cyclase, in regulating terminal differentiation of these cells was explored by stable transfection of fibroblasts expressing wild-type and a constitutively active mutant of Gi alpha 2 (Q205L). Under the influence of the cytomegalovirus promoter, the expression vector yielded a 1.7-fold (Q205L mutant Gi alpha 2) and 2.2-fold (wild-type Gi alpha 2) increase in steady-state levels of these G protein alpha-subunits. Elevation of Gi alpha 2 expression or expression of constitutively active Gi alpha 2 (Q205L) promoted lipid accumulation in these clones, the hallmark of terminal differentiation of 3T3-L1 fibroblasts to adipocytes. Increasing Gi alpha 2 activity promotes adipogenic conversion, as was previously observed by decreasing Gs alpha either by inducers of differentiation or by oligodeoxynucleotides antisense to Gs alpha. Thus Gs alpha and Gi alpha 2 are shown to be counterregulatory with respect to promoting differentiation of 3T3-L1 mouse embryo fibroblasts to adipocytes in the absence of exogenously added inducers of differentiation. This is the first report demonstrating the induction of terminal differentiation of cells by the overexpression of a G protein alpha-subunit, further implicating G proteins as regulators of complex biological responses such as adipogenesis.

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