A truncated progesterone receptor (PR-M) localizes to the mitochondrion and controls cellular respiration.

The cDNA for a novel truncated progesterone receptor (PR-M) was previously cloned from human adipose and aortic cDNA libraries. The predicted protein sequence contains 16 unique N-terminal amino acids, encoded by a sequence in the distal third intron of the progesterone receptor PR gene, followed by the same amino acid sequence encoded by exons 4 through 8 of the nuclear PR. Thus, PR-M lacks the N terminus A/B domains and the C domain for DNA binding, whereas containing the hinge and hormone-binding domains. In this report, we have localized PR-M to mitochondria using immunofluorescent localization of a PR-M-green fluorescent protein (GFP) fusion protein and in Western blot analyses of purified human heart mitochondrial protein. Removal of the putative N-terminal mitochondrial localization signal obviated association of PR-M with mitochondria, whereas addition of the mitochondrial localization signal to green fluorescent protein resulted in mitochondrial localization. Immunoelectron microscopy and Western blot analysis after mitochondrial fractionation identified PR-M in the outer mitochondrial membrane. Antibody specificity was shown by mass spectrometry identification of a PR peptide in a mitochondrial membrane protein isolation. Cell models of overexpression and gene silencing of PR-M demonstrated a progestin-induced increase in mitochondrial membrane potential and an increase in oxygen consumption consistent with an increase in cellular respiration. This is the first example of a truncated steroid receptor, lacking a DNA-binding domain that localizes to the mitochondrion and initiates direct non-nuclear progesterone action. We hypothesize that progesterone may directly affect cellular energy production to meet the increased metabolic demands of pregnancy.

Association of maternal IL-1 receptor antagonist intron 2 gene polymorphism and preterm birth.

OBJECTIVE: This study was undertaken to determine whether the interleukin-1 receptor antagonist (IL-1RN) variable number tandem repeat polymorphism is associated with preterm birth. STUDY DESIGN: A case-control study was performed. Cases (n = 95) delivered before 37 weeks after preterm labor (PTL) or preterm premature rupture of membranes (PPROM) and controls (n = 105) delivered after 37 weeks. Maternal DNA was genotyped by polymerase chain reaction for a length polymorphism in intron 2 of the IL-1RN gene. RESULTS: There was no significant difference in maternal age, ethnicity, insurance status, or parity between groups. Allele and genotype frequencies did not differ significantly from that expected under Hardy-Weinberg equilibrium (P = .59) in the total group as well as study groups. Of the 95 cases, 26.8% had at least 1 copy of allele 2 present compared with 12.4% in the control group (P < .0004). CONCLUSION: Maternal carriage of at least 1 copy of the IL-1RN allele 2 appears to be associated with increased risk of preterm birth.