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. Author manuscript; available in PMC: 2005 Sep 21.
Published in final edited form as: Exp Biol Med (Maywood). 2003 Dec;228(11):1272–1281. doi: 10.1177/153537020322801106

Figure 1.

Figure 1

The possible heterogeneity in steroid-binding proteins involved in mediating nongenomic steroid actions is depicted hypothetically in these diagrams. Each lettered panel depicts a steroid receptor with a different protein class identity (symbols numbered 1–5). Steroid receptors or steroid-binding proteins also have a small circle labeled “S” (for steroid) attached to them. Alternate shapes depict different protein class identities, while alternate fill patterns depict different conformations of a single protein (e.g., 1 vs. 1-crosshatched for nuclear receptor versus nuclear receptor in the membrane in Panel A). Many of these different protein classes and their partners can be regulated by their phosphorylation status (shown by -P). Some signal cascades may culminate in the post-translational modification of transcription factors (symbols labeled “TF” in all panels, also see symbol 1-crosshatched in Panels A and F), making these effects ultimately genomic. Protein partners or targets of steroid receptors (unlabeled geometric shapes) can be located outside the cell, inside the cell, or in the membrane (all panels). The membrane indentation (all panels) refers to the residence of many signaling proteins, including membrane receptors, in membrane rafts or caveolae. For economy of design, some panels and symbols represent different kinds of proteins, as described below. Classes of proteins that bind steroids and participate in initially nongenomic responses could include: classical nuclear-type receptors in a membrane location (Panel A, Protein 1), blood-borne (Panel B, Protein 2), or intracellular (Panel C, Protein 3) steroid-binding proteins, enzymes (Panel C, Protein 3), transporters or channels or other known membrane receptors (Panel D, Protein 4), or entirely new receptors (Panel E, Protein 5). Multiple signaling pathways with numerous steps and directions (arrows) may convene on, and emanate from, these protein clusters, depending upon the cellular signaling context. These combinatorial effects can lead to response complexity. Shown in Panel F, multiple steroid-binding proteins may participate in signaling cascades leading to multiple functions in the same cell.