Membrane initiated steroid signaling (MISS): computational, in vitro and in vivo evidence for a plasma membrane protein initially involved in genomic steroid hormone effects.

Steroid hormones are indispensable for control of vital processes, development, reproduction and modulation of behavior. Lack or complete dysfunction of glucocorticoid (GC) signaling, in particular, have lethal consequences. Even a minor change in the level of circulating cortisol can be of physiological and clinical significance. Analysis of the action mechanisms of GC is therefore of major importance, especially since natural and synthetic GC are widely used in the therapy of GC-responsive diseases. According to the classical genomic concept of steroid hormone action, the effects of GC are mediated by specific nuclear receptors (GR). Recent findings provide evidence for the existence of additional, plasma membrane (PM) located steroid receptors, which are thought to be responsible for rapid, non-genomic responses. We present evidence for a PM-residing protein, termed "steroid hormone recognition and effector complex" (SHREC), which plays a pivotal role in the complex network of PM-related non-genomic responses leading to GR-mediated genomic effects. This conclusion was drawn from studies using different in vitro and in vivo models of a GC-target: (1) highly purified fractions of osmotically active PM-vesicles isolated from rat and human hepatocytes, (2) a computational model of SHREC generated by the "automated receptor modeling" (ARM) method, (3) rat liver cell lines transfected with a GC-responsive reporter gene construct and (4) young women orally administered with selected steroids. We conclude that SHREC and the GR participate in the same signaling chain, SHREC<-->steroid interaction is the initial step and an interdependent part of the complete GC signal propagation, thus called "membrane initiated steroid signaling" (MISS).

Association of progesterone receptor polymorphism with recurrent abortions.

OBJECTIVE: The current study sought for polymorphisms within the progesterone receptor (PR) gene. Allele and genotype frequencies of patients with repeated abortions were compared to a control group. DESIGN: All exons of the PR of 42 women with repeated abortions and 40 controls were screened for single nucleotide polymorphisms (SNP). Determination of the DNA-sequences was performed. RESULTS: Three SNPs were detected (exon 1: G1031C Ser344Thr; exon 4: G1978T Leu660Val, exon 5: C2310T His770His). These SNPs are linked. The more frequent wildtype (*1) allele and the rarer (*2) allele were found in the control group and in the study group at different frequencies (control group: *1/*1: 78%, *1/*2: 22%, *2/*2: 0%; patient group: *1/*1: 50%, *1/*2: 43%, *2/*2: 7%). The genotypes distributions differed significantly from each other (P=0.019, chi2=7.879). CONCLUSIONS: The data suggest that the rarer PR allele may be associated with an increased likelihood of repeated miscarriages contributing to its multi-factorial causes.

Membrane-initiated steroid signaling (MISS): genomic steroid action starts at the plasma membrane.

UNLABELLED: Plasma membrane (PM) steroid recognition sites are thought to be responsible only for rapid, non-genomic responses without any link to the nuclear receptor-mediated genomic effects of steroids. We focused on a PM "glucocorticoid-importer" (GC-importer) that imports GC into rat liver cells. This site interacts also with particular gestagens (progesterone, P; medroxyprogesterone, MP; ethynodiol, Ethy) and estrogens (ethinylestradiol, EE(2); mestranol), which do not bind to the nuclear GC receptor (GR). To elucidate the role of the GC-importer, we transfected a rat wild-type hepatocyte (CC-1) and a hepatoma cell line, unable to import GC (MH 3924), with a GC<-->GR-responsive luciferase (luc)-reporter gene. Selected steroids were tested for their ability to induce or inhibit luc expression. Corticosterone (B) and dexamethasone (Dex), but also the GC-antagonists cortexolone (Cortex), P and MP, induced luc. Even the PM-impermeable BSA-derivatives of B, Dex and Cortex did so to almost the same extent as the free steroids. MH 3924 cells respond stronger than CC-1 to luc inducing steroids. Luc expression was inhibited by RU 38 486, but also by EE(2) and Ethy. The thiol reactive mesylate-derivatives of B, Dex and Cortex induced to a considerably lesser extent than the free or BSA-steroids. The thiol reagent mersalyl blocks cellular entry of GC and inhibits luc induction in CC-1 cells. Incubation with EE(2) and B of PM-vesicles, isolated from liver cells, resulted in a decrease of the density of two 75 and 52kDa G-proteins reflecting a diminished exchange of GDP by GTP. CONCLUSION: the PM-residing GC-importer, now renamed "Steroid Hormone Recognition and Effector Complex" (SHREC) is an interdependent part of the complete GC signal propagation in which G-proteins are involved. Free SH-groups of SHREC are a prerequisite for genomic GC activity. Specific interactions between SHREC and GC-agonist/-antagonist trigger steroid-dependent signaling. However, import of the ligand into the cell terminates it. Thus, the PM-related non-genomic steroid responses are clearly linked to the GR-related genomic effects.