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Journal of Clinical Endocrinology & Metabolism , doi:10.1210/jc.2005-1807
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The Journal of Clinical Endocrinology & Metabolism Vol. 91, No. 6 2366-2372
Copyright © 2006 by The Endocrine Society

Thrombin and Interleukin-1ß Regulate HOXA10 Expression in Human Term Decidual Cells: Implications for Preterm Labor

Jennifer L. Sarno, Frederick Schatz, Charles J. Lockwood, S.-T. Joseph Huang and Hugh S. Taylor

Yale University School of Medicine, New Haven, Connecticut 06520

Address all correspondence and requests for reprints to: Hugh S. Taylor, M.D., Associate Professor, Division of Reproductive Endocrinology and Fertility, Department of Obstetrics, Gynecology, and Reproductive Sciences, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06520. E-mail: hugh.taylor{at}yale.edu.


   Abstract
Top
 Abstract
Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
Context: Preterm delivery is commonly caused by intraamniotic infection with expression of proinflammatory cytokines (IL-1ß) or by abruption resulting in generation of decidual thrombin. Although human parturition is not preceded by overt progesterone withdrawal, progesterone resistance likely leads to labor. The uteri of Hoxa10(–/–) mice demonstrate progesterone resistance; several genes, including prostaglandin receptors, are inappropriately regulated in response to progesterone.

Objective: We hypothesized that IL-1ß or thrombin would decrease HOXA10 expression, contributing to the progestin-resistant environment. We analyzed expression of HOX genes and their regulation by IL-1ß or thrombin in decidual cells.

Design and Setting: We conducted an in vitro experiment at an academic medical center.

Intervention: Term decidual cells were treated with estradiol (E2) or E2 plus medroxyprogesterone acetate followed by addition of thrombin or IL-1ß.

Main Outcome Measure: HOX mRNA was evaluated by microarray and confirmed by quantitative RT-PCR. Protein expression was detected using immunohistochemistry and Western analysis.

Results: HOXA9, HOXA10, and HOXA11 were expressed in decidual cells and regulated by IL-1ß and thrombin. HOXA10 was further analyzed because of its association with progesterone responsiveness. After E2 treatment, IL-1ß and thrombin decreased HOXA10 mRNA by 94 and 81%, respectively. After E2 plus medroxyprogesterone acetate treatment, IL-1ß and thrombin resulted in an 86 and 72% decrease in HOXA10 mRNA, respectively. A similar decrease was noted in HOXA10 protein expression.

Conclusion: The expression of HOXA10 protein at term indicates that it may have a role in maintaining decidual cell phenotype and pregnancy. The dramatic decrease of HOXA10 in response to IL-1ß or thrombin may contribute to progestin resistance in preterm labor, mimicking progesterone resistance seen in Hoxa10(–/–) mice.


   Introduction
Top
 Abstract
 Introduction
Subjects and Methods
 Results
 Discussion
 References
 
PRETERM DELIVERY (PTD) is a leading cause of infant mortality in the United States (1, 2, 3). Augmented expression of proinflammatory cytokines in the uterus has been linked to PTD (4, 5, 6, 7). Levels of these cytokines, primarily IL-1ß, can increase with or without overt intrauterine infection. Cytokines dramatically affect the expression of cyclooxygenase-2 and augment the expression of prostaglandin receptors in the decidua, fetal membranes, and/or myometrium that ultimately elicit enhanced decidual, fetal membrane, and cervical protease production promoting preterm premature rupture of the membranes as well as cervical shortening and myometrial contractions promoting preterm labor (PTL) (2). PTD is also frequently associated with abruption or decidual hemorrhage that results in intense local thrombin generation (8, 9, 10, 11, 12, 13, 14). Thrombin, binding to protease-activated receptor-1, stimulates both decidual protease production to promote preterm premature rupture of the membranes and myometrial contractions to induce PTL (10, 11, 15).

The initial site of inflammatory cytokine action in PTL, caused by either intraamniotic infection or abruption, is the decidua. During the midluteal phase of the human menstrual cycle, progesterone transforms the estradiol (E2)-primed stromal cells into decidual cells (16). The homeobox gene HOXA10 (human)/Hoxa10 (mouse) is necessary for normal decidualization and decidual function; Hoxa10 null mice exhibit impaired decidualization and failed embryo implantation (17, 18). HOXA10 is regulated by progesterone and in turn augments progesterone responsiveness (17, 19, 20). In stromal cells, Hoxa10 regulates the expression of several markers of decidualization, including IGF-binding protein 1 (IGFBP-1) and prolactin (17, 21, 22, 23, 24). In the first trimester of pregnancy, IGFBP-1 regulates cytotrophoblast invasion of the decidua, whereas decidual cell-derived prolactin appears to be involved in conferring immune tolerance to the embryo (25). In term decidual cells, the roles of IGFBP-1 and prolactin are less clear, whereas progestin-enhanced plasminogen activator inhibitor 1 and matrix metalloproteinase expression protect against PTD by suppressing a proteolytic cascade targeting decidual and fetal membrane extracellular matrix (10, 11). The current study evaluated expression of HOXA10 mRNA in term decidual cells and the effects of sex steroids and inflammatory cytokines on its expression. We hypothesized that, as demonstrated in stromal and decidual cells in the menstrual cycle and early pregnancy (19, 26), HOXA10 would be expressed and regulated in this cell type at term. The expression of HOXA10 is necessary for the function of these cells early in pregnancy and maintains their ability to regulate genes in response to progesterone (17, 19, 26). HOXA10 may similarly contribute to the function of this cell type at term, including regulating progesterone response.

Progesterone action in both decidua and myometrium is normally required for the maintenance of pregnancy (27, 28, 29). In most species, labor is initiated by progesterone withdrawal. Progesterone withdrawal at term initiates labor in animals including sheep, mice, and rats (30, 31), although overt progesterone withdrawal does not occur in human parturition (32, 33, 34, 35). Prostaglandins are the ultimate arbiters of labor (36, 37, 38, 39), and their synthesis is increased by proinflammatory cytokines (40, 41, 42, 43, 44, 45, 46, 47) or progesterone withdrawal (48, 49), demonstrating a common mechanism for both PTD and parturition at term. Prostaglandin receptors are a target of progesterone regulation throughout pregnancy, and a delicate balance of relaxatory and contractile receptors either maintains the quiescence of the uterus or initiates contractions at the time of labor.

The progesterone responsiveness of prostaglandin receptors is in part regulated by HOXA10 (18). Hoxa10-deficient mice demonstrate aberrant expression of prostaglandin E receptors EP3 and EP4. In wild-type mice, the decidua responds to progesterone with an increase in both EP3 and EP4. However, in Hoxa10(–/–) mice, progesterone fails to fully up-regulate the expression of these receptors (18). The initiation of human labor is not caused by progesterone withdrawal but rather is thought to be initiated by the creation of a progesterone-resistant uterine environment. Similar to the progestin resistance seen in the decidua of Hoxa10(–/–) mice, reduced HOXA10 expression likely also leads to progestin resistance.

HOX gene expression in term decidua has not been characterized, nor have the effects of inflammatory cytokines on HOX gene expression been examined in any system. Here we determine that HOXA10 was expressed in term decidual cells and also report the effect of IL-1ß and thrombin treatment on HOXA10 expression. The results of this study suggest the involvement of HOXA10 in the maintenance of pregnancy and in molecular pathways downstream of IL-1ß and thrombin that may contribute to preterm labor.


   Subjects and Methods
Top
 Abstract
 Introduction
 Subjects and Methods
Results
 Discussion
 References
 
Term decidual cell isolation and culture conditions

Decidua was collected from seven women at cesarean delivery after uncomplicated pregnancies. Samples were collected after informed consent under an approved human investigations committee protocol. Term stromal/decidual cells from these samples were isolated and purified to homogeneity on a Percoll gradient and passaged until more than 99% free of CD45+ cells as determined by FACS analysis as previously described (50). At confluence, the cells were primed with either 10–8 M E2 or 10–8 M E2 plus 10–7 M medroxyprogesterone acetate (MPA) for 7 d to simulate the steroidal milieu of pregnancy and then switched to serum-free defined medium containing the corresponding steroids with either 2.5 U/ml thrombin or 1 ng/ml IL-1ß. After 6 h, total RNA was isolated (RNeasy Mini Kit; QIAGEN, Germantown, MD).

Microarray

Term stromal/decidual cells from three women were grown to confluence in Falcon T-25 flasks. Cells were harvested with QIAzol lysis reagent (QIAGEN, Valencia, CA) and used to prepare total RNA. According to the manufacturer’s instruction, 100 µg total RNA was precipitated using RNeasy Mini Kit (QIAGEN, Valencia, CA) to prepare the template for cDNA synthesis. A T7-(dT)24 oligo-primer was used to synthesize double-stranded cDNA by the One-Cycle cDNA Synthesis Kit (Affymetrix Inc., Santa Clara, CA), which was subsequently purified using Sample Cleanup Module (Affymetrix) and ethanol precipitation. Then GeneChip IVT Labeling Kit (Affymetrix) was used to generate biotinylated cRNA. Additional cRNA purification was carried out using Sample Cleanup Module before the fragmentation of biotinylated cRNAs with 5x fragmentation buffer (200 mM Tris, pH 8.1, 500 mM KOAc, 150 mM MgOAc). The chemically fragmented cRNAs were then hybridized on Affymetrix HG_U133 Plus 2.0 human chips in GeneChip Hybridization Oven 640 (Affymetrix), screening for approximately 47,400 human genes and expressed sequence tags followed by fluorescence labeling with Fluidics Station 450 (Affymetrix) and optical scanning with Affymetrix GeneChip Scanner 3000 by W. M. Keck Foundation Biotechnology Resource Laboratory at Yale University.

Raw data without normalization generated from Affymetrix GeneChip operating software version 1.1.1 (GCOS 1.1.1) (Affymetrix) were analyzed by GeneSpring software 7.2 (Silicon Genetics, Redwood City, CA). The gene readouts were normalized to the 50th percentile of the distribution of all measurements in each chip. Per-gene normalization was performed using the median value of each gene throughout different chips in the same experimental condition. The normalized data were first filtered to eliminate the genes with absent call in all experimental conditions. Then a parametric test assuming unequal variance was applied to test the statistical significance. Fold ratios were derived from comparing normalized data between control and treatment groups. HOX genes up- or down-regulated more than 2.0-fold by E2 plus MPA vs. E2 plus MPA plus IL-1 ß or thrombin were filtered.

Real-time PCR

HOXA10 mRNA levels were evaluated by quantitative real time RT-PCR and normalized to ß-actin using the Roche LightCycler (Roche, Indianapolis, IN). The reaction was carried out using the LightCycler RNA Master SYBR Green I kit. Reaction conditions included 1.0 µg RNA; 2 mM or 3 mM Mn[OAc]2 for HOXA10 and ß-actin, respectively; 150 nM of each primer; and 1x RNA Master SYBR Green for a final reaction volume of 20 µl. Primer sequences for each gene are as follows: HOXA10, 5'-AGGTGGACGCTGCGGCTAATCTCTA-3' and 5'-GCCCCTTCCGAGAGCAGCAAAG-3' (51); ß-actin, 5'-CGTACCACTGGCATCGTGAT-3' and 5'-GTGTTGGCGTACAGGTCTTTG-3' (52).

RT was carried out for 30 min at 61 C, followed by initial denaturation at 95 C for 30 sec and 45 cycles of PCR including denaturation at 95 C for 2 sec; annealing at 65 C (HOXA10), 62 C (ß-actin), or 58 C (EP4) for 5 sec; and elongation at 72 C for 14 sec. A melting curve was created after the amplification to observe the specificity of the primers or number of products amplified. Treatment was carried out and analyzed under each condition using seven decidual cell samples obtained from different individuals. Comparisons between treatment groups were analyzed by ANOVA.

Immunohistochemistry

To demonstrate HOXA10 protein expression in term decidual cells, decidua was collected after a term cesarean delivery performed for breech presentation. The tissue was subsequently fixed in formalin and paraffin embedded, and immunohistochemistry was performed as previously described (53, 54). Briefly, slides were deparaffinized and dehydrated through a series of xylene and ethanol washes, followed by permeabilization in 95% cold ethanol. After a 5-min rinse in distilled water (dH20), an antigen-presenting step was performed by steaming the slides in 0.01 M sodium citrate buffer for 20 min, followed by removal of the staining jar from the steam chamber and cooling for 20 min. Slides were rinsed for 5 min in PBS with 0.1% Tween 20 (PBST), and sections were circumscribed with a hydrophobic pen. Endogenous peroxidase was quenched with 3% hydrogen peroxide for 5 min followed by a 5-min PBST wash. Nonspecific binding was blocked with 1.5% normal horse serum in PBST for 1 h at room temperature. Slides were incubated in goat polyclonal HOXA10 (sc-17159; Santa Cruz Biotechnology, Santa Cruz, CA) at 1:3000 overnight at 4 C. Normal goat IgG (Santa Cruz Biotechnology) was used as a negative control. Slides were washed in 1x PBST. Biotinylated horse antigoat (Vector Laboratories, Burlingame, CA) was applied at 3.5 µg/ml for 1 h at 4 C. Slides were washed in 1x PBST, incubated in ABC Elite (Vector) for 15 min at room temperature, washed in 1x PBST, and incubated for 5 min in diaminobenzidine (Vector). A 20-sec exposure to hematoxylin was used as a counterstain. Slides were rehydrated through 3-min ethanol and xylene washes and mounted with Permount.

Western analysis

Cells were washed once with PBS, harvested into 100 ml passive lysis buffer [50 mM Tris (pH 7.5), 5 mM MgCl2, 5 mM EGTA, 10% glycerol, 0.25% Triton X-100, containing a 1:100 dilution of a freshly added protease inhibitor cocktail (Sigma P8340; Sigma Chemical Co., St. Louis, MO)], passed through a 22-gauge 1.5-inch needle, and incubated on ice for 30 min. The cell lysate was centrifuged at 10,000 x g for 10 min at 4 C, and the supernatant was transferred to a new tube. Samples were quantified using the Bio-Rad protein assay kit. Thirty-five micrograms of cell lysate were separated on a 7.5% SDS-PAGE gel and transferred to nitrocellulose. After blocking in PBS containing 5% milk and 0.1% Tween 20 overnight at 4 C, the membrane was incubated with goat anti-HOXA10 (Santa Cruz Biotechnology) at 1:200 or monoclonal ß-actin antibodies at 1:20,000 (Sigma A5441) for 1 h at room temperature. The membrane was then washed three times for 5 min each with wash buffer (1x PBS/0.1% Tween). The blot was incubated in a 1:1000 dilution of horseradish peroxidase-conjugated secondary antibodies (Santa Cruz Biotechnology) for 1 h at room temperature. The membrane was washed three times for 5 min each with wash buffer, and bands were visualized using chemiluminescence (ECL; Amersham Biosciences, Piscataway, NJ).


   Results
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
Discussion
 References
 
IL-1ß and thrombin decrease homeobox gene expression

Leukocyte-free term stromal/decidual cells were treated with either IL-1ß or thrombin, two molecules implicated in the initiation of preterm labor. Genes affected by the treatment were analyzed by microarray. Several homeobox genes that have been previously reported to be expressed in the female reproductive tract were identified in the array. Figure 1Go shows the average decrease in HOX gene expression with thrombin or IL-1ß treatment. Among E2-treated cultures, IL-1ß treatment resulted in the most significant decrease in HOX expression, with HOXA9, HOXA10, and HOXA11 expression decreased 6.00-, 6.02-, and 4.71-fold, respectively, compared with cultures treated with E2 alone. Term decidual cells treated with E2 plus MPA and subsequently with IL-1ß demonstrated a smaller yet significant decrease in HOX expression, with HOXA9, HOXA10, and HOXA11 expression decreased 5.31-, 4.8-, and 4.2-fold, respectively, compared with cultures treated with E2 plus MPA alone. Thrombin treatment resulted in decreased HOX gene expression; HOXA9, HOXA10, and HOXA11 each decreased 2.37-, 2.57-, and 2.19-fold, respectively, compared with E2-treated controls. Term decidual cells pretreated with E2 plus MPA and subsequently with thrombin also demonstrated a statistically significant greater than 2-fold decrease in HOX gene expression; HOXA11 showed the greatest decrease, declining 3-fold compared with cultures treated with E2 plus MPA alone. Effects of IL-1ß and thrombin on HOXA9, HOXA10, and HOXA11 were all statistically significant.


Figure 1
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  		FIG. 1. HOXA9, -A10, and -A11 expression was decreased in term stromal/decidual cells treated with IL-1ß or thrombin. Microarray analysis revealed a statistically significant decrease in HOX gene expression in term decidual cells treated with IL-1ß (I) or thrombin (T) compared with E2 (E) or E2 plus MPA (EM)-treated controls. Raw microarray data were normalized using the median value of each gene throughout different chips in the same experimental condition. Fold ratios were derived from comparing normalized data between control and treatment groups. Genes up- or down-regulated more than 2.0-fold by IL-1ß or thrombin were filtered. P values of EI and ET are in comparison with E2-treated controls, and P values for EMI and EMT are in comparison with EM-treated controls. n = 3 in each treatment group.

 
HOXA10 is expressed in human term decidual cells in vivo

To verify that HOXA10 protein was expressed in term decidua in vivo, endometrial samples were collected after term cesarean delivery performed for breech presentation. Immunohistochemistry revealed that HOXA10 protein was present in term decidual cells from a noncontracting uterus at term (Fig. 2Go). Normal goat IgG was used as a nonspecific control antibody (Fig. 2AGo). HOXA10 expression has been previously well characterized in secretory endometrium; this tissue was used as a positive control and for comparison. Endometrium collected at d 23 of the menstrual cycle demonstrated HOXA10 expression in the glands and the majority of stromal cells (Fig. 2BGo). Term decidua demonstrated HOXA10 protein expression in the majority of decidual cells (Fig. 2CGo).


Figure 2
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  		FIG. 2. Term decidua expressed HOXA10 protein in vivo. Endometrial tissue was collected from luteal phase or term cesarean section and analyzed for HOXA10 expression by immunohistochemistry. A, Endometrium immunostained with a nonimmune goat IgG antibody as a negative control; B, endometrium from the luteal phase of the menstrual cycle expressed HOXA10 protein; C, term decidua from an uncomplicated pregnancy expressed HOXA10 protein. Strong nuclear HOXA10 expression is seen in almost all endometrial epithelial and stromal cells as well as decidual cells. Photographs were taken at x20 magnification.

 
IL-1ß and thrombin decrease HOXA10 mRNA and protein expression

Of the homeobox genes affected by IL-1ß and thrombin in the microarray screen, HOXA10 is known to regulate progesterone action, because Hoxa10(–/–) mice demonstrate progesterone resistance (18). In humans, labor may be initiated by alteration of the uterus from a state of progesterone responsiveness to progesterone resistance. Therefore, we confirmed the effect of IL-1 ß and thrombin on HOXA10 expression in term stromal/decidual cells. mRNA from the term stromal/decidual cells used in the microarray was analyzed for HOXA10 expression by quantitative real-time RT-PCR (Fig. 3Go). In E2-treated cultures, IL-1ß and thrombin decreased HOXA10 by 94 and 81%, respectively (P < 0.001) (Fig. 3AGo). Cultures treated with E2 plus MPA demonstrated an average 53% decrease in HOXA10 expression compared with cultures treated with E2 alone (Fig. 3AGo). Addition of IL-1ß or thrombin to cultures maintained in E2 plus MPA resulted in an 86 and 72% decrease in HOXA10 expression, respectively (P < 0.001) (Fig. 3BGo). After treatment of stromal/decidual cells with either E2 or EP, HOXA10 protein expression was similarly greatly decreased by IL-1ß or thrombin as demonstrated by Western analysis (Fig. 4Go).


Figure 3
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  		FIG. 3. IL-1ß and thrombin significantly decreased HOXA10 mRNA expression in term stromal/decidual cells in vitro as determined by real-time RT-PCR. A, In E2-treated cells (E), IL-1ß (I) and thrombin (T) decreased HOXA10 by 94 and 81%, respectively. MPA treatment (M) decreased levels of HOXA10 by 53%. B, In E2 plus MPA-treated cells (EM), IL-1ß (I) and thrombin (T) decreased HOXA10 by 86 and 72%, respectively. For all IL-1ß and thrombin treatments, P < 0.001 compared with E- or EM-treated controls. n = 7 in each treatment group.

 

Figure 4
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  		FIG. 4. IL-1ß and thrombin significantly decreased HOXA10 protein expression in term stromal/decidual cells in vitro as determined by Western analysis. A, In E2-treated cells (E), IL-1ß (I) and thrombin (T) greatly decreased HOXA10 expression. In E2 plus MPA-treated cells (EM), IL-1ß (I) and thrombin (T) similarly decreased HOXA10. n = 3 in each treatment group.

 

   Discussion
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
References
 
Early PTD at less than 33 wk gestation is a leading cause of infant mortality in the United States (1, 2, 3). The two most common etiologies of early PTD are intrauterine infection and abruption. The former results in enhanced expression of proinflammatory cytokines in the fetal membranes and decidua, whereas the latter results in increased decidual thrombin generation (4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15). Here we describe a common pathway involving HOXA10 by which IL-1ß and thrombin may contribute to the initiation of labor.

This is the first study to demonstrate the expression of any of the HOX genes in term decidual cells. HOX genes are expressed in a phase-dependent manner during the menstrual cycle and are necessary for decidualization and implantation (19, 55, 56). Here we have demonstrated that HOX genes are expressed at term and likely throughout pregnancy. The expression of HOXA10 protein at term indicates that it may have a role in maintaining decidual phenotype throughout pregnancy. The presence of HOXA10 near term also implicates this protein as having a potential role in maintaining progesterone responsiveness and preventing preterm labor.

Progesterone resistance is a postulated method by which labor is initiated in humans (27, 28). A potential consequence of decreased HOXA10 expression is the creation of a progesterone-resistant environment in the decidua. Hoxa10(–/–) mice display progesterone resistance; EP3 and EP4 are inappropriately regulated in response to progesterone (18). The dramatic decrease in HOXA10 expression seen after IL-1ß or thrombin treatment may mimic the uterine environment seen in the Hoxa10(–/–) mouse. The diminished progesterone responsiveness of uterine prostaglandin receptors (and likely multiple additional molecules) may mimic the response to progestin withdrawal seen in other species. The loss of HOXA10 expression may lead to lack of progesterone response and therefore functional progesterone withdrawal.

The action of prostaglandins on each receptor leads to different intracellular events. EP1 and prostaglandin F receptor lead to intracellular calcium mobilization, and EP3 inhibits the adenylate cyclase; these actions induce a contractile signal. EP2 and EP4 both increase adenylate cyclase, which allows muscle relaxation (57, 58, 59, 60, 61, 62, 63, 64, 65, 66). The expression pattern of the receptors changes during pregnancy and labor, which may lead to differential tissue response to prostaglandins (61, 62, 63). Progesterone in part controls the spatial and temporal expression of prostaglandin receptors during pregnancy and labor. In sheep and rats at term, the level of progesterone significantly decreases (64, 65, 66). As a result, the expression of the contractile receptors EP3 and prostaglandin F receptor is up-regulated, and that of the relaxatory receptor EP2 is down-regulated. Interestingly, the relaxatory receptor EP4 is also up-regulated during labor. It is likely that the regulation of the prostaglandin receptors, and therefore the increased sensitivity of the uterus to prostaglandins, is responsible for controlling uterine contractions. Here decreased HOXA10 is expected to alter the balance of relaxatory and contractile receptors.

HOXA10 is a known regulatory target of progesterone in the endometrium during the menstrual cycle, where it is an essential mediator of progesterone function, necessary for endometrial receptivity (17, 19, 26, 56). Hoxa10 null mice lack endometrial receptivity and do not conceive, which prohibits the examination of Hoxa10 loss on parturition (67). However, in the endometrium, HOXA10 is known to mediate the pleiotropic effects of progesterone (17). HOXA10 regulates several known progesterone-responsive genes, including ß3 integrin subunit (68), EMX2 (69, 70), IGFBP-1 (23), and EP3 and EP4 (18). HOXA10, itself induced by progesterone, in turn regulates a subset of progesterone-responsive genes; these targets of HOXA10 regulation may not be directly progesterone regulated or only partially so. Loss or decrease of HOXA10 may similarly diminish progesterone action.

Three HOX genes were down-regulated in response to IL-1ß and thrombin. HOXA11 is known to be regulated by progesterone, whereas the progesterone responsiveness of HOXA9 has not been examined (55). These HOX proteins may also contribute to progesterone responsiveness. Although progesterone withdrawal does not initiate labor in humans, other members of the progesterone signaling pathway, potentially including several HOX genes, are affected, resulting in progesterone resistance. Two known mediators of PTL, thrombin and IL-1ß, operate in a common pathway that results in reduced expression of HOXA10 and thereby diminishes the ability to maintain uterine progesterone responsiveness.


   Footnotes
 
This work was supported by National Institutes of Health Grants HD36887 (to H.S.T.), ES10610 (to H.S.T.), and HL07004 (to C.J.L.).

All authors have nothing to declare.

First Published Online March 21, 2006

Abbreviations: E2, Estradiol; EP, prostaglandin E receptor; IGFBP-1, IGF-binding protein 1; MPA, medroxyprogesterone acetate; PBST, PBS with 0.1% Tween 20; PTD, preterm delivery; PTL, preterm labor.

Received August 10, 2005.

Accepted March 14, 2006.


   References
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

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