A Novel Nuclear Signaling Pathway for Thromboxane A₂ Receptors in Oligodendrocytes: Evidence for Signaling Compartmentalization during Differentiation

Abstract

The present study investigated G protein expression, localization, and functional coupling to thromboxane A₂ receptors (TPRs) during oligodendrocyte (OLG) development. It was found that as OLGs mature, the expression levels of G_q increase while those of G₁₃ decrease. In contrast, the expression levels of G_s, G_o, and G_i do not change significantly. Localization studies revealed that G_q, G₁₃, and G_i are present only in the extranuclear compartment, whereas G_s and G_o are found in both the extranuclear and the nuclear compartments. Purification of TPR-G protein complexes demonstrated that TPRs couple to both G_q and G₁₃ in the extranuclear compartment but only to G_s in the nuclear compartment. Furthermore, functional analysis revealed that stimulation of nuclear TPR in OLGs stimulates CREB phosphorylation and myelin basic protein transcription and increases survival. Collectively, these results demonstrate that (i) OLGs selectively modulate the expression of certain G proteins during development, (ii) G proteins are differentially localized in OLGs leading to subcellular compartmentalization, (iii) TPRs couple to G_q and G₁₃ in the extranuclear compartment and to G_s only in the nucleus, (iv) mature OLGs have a functional nuclear TPR-G_s signaling pathway, and (v) nuclear TPR signaling can stimulate CREB phosphorylation and myelin gene transcription and increase cell survival. These findings represent a novel paradigm for selective modulation of G protein-coupled receptor-G protein signaling during cell development.

ACKNOWLEDGMENTS

We thank S. Srinivasan and J.-S. Huang for assistance with the cAMP assay and L. Dong for her help with primary cell culture. We also thank F. Khaswaneh for critical reading of the manuscript.

This work was supported in part by a grant from the National Multiple Sclerosis Society (RG 3054B2/1) awarded to G.C.L.