A Truncated Progesterone Receptor (PR-M) Localizes to the Mitochondrion and Controls Cellular Respiration

Abstract

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.

Expression of a mitochondrial progesterone receptor in human spermatozoa correlates with a progestin‐dependent increase in mitochondrial membrane potential

“…RNAi studies in T47D breast cancer cells and overexpression in TET-On HeLa cells reveal a ligand-dependent control of cellular respiration. Progestin treatment shows an increase in mitochondrial membrane potential (ψ m ) and oxygen consumption, consistent with increased cellular respiration (Dai et al, 2013). …”

“…We have previously identified a novel, truncated PR localized to the outer membrane of the mitochondrion, named PR-M (Dai, et al, 2013). Originally cloned from human adipose and aortic cDNA libraries (Saner, et al, 2003), transcript analysis shows a novel sequence derived from the distal 3 rd intron of the PR gene, consistent with a mitochondrial localization signal (MLS), followed by the same sequence for exons 4 through 8 of nuclear PR.…”

Mitochondrial determinants of cancer health disparities

“…In fact, a truncated PR (PR-M) has been cloned from human adipose and aortic cDNA libraries [320]; the encoded protein lacks the DNA-binding and regulatory domains but retains the hormone-binding domain. Subsequently, Dai et al showed that the PR-M localizes to the mitochondria of T47D breast epithelial cells and HeLa cells [81]. The functionality of PR-M was established by an increase in mitochondrial membranes and increased cellular respiration upon exposure to progestin.…”

Mitochondrial Hormone Receptors - an Emerging Field of Signaling in the Cell’s Powerhouse

“…A mitochondrial progesterone receptor (PR) has been demonstrated and discussed in terms of nongenomic effects [10][11][12][13]. These actions concern respiratory activity, such as increased mitochondrial membrane potential and oxygen consumption [10][11][12], a role that would be in line with metabolism-enhancing properties of property of progesterone, as known from the postovulatory increase in temperature.…”

“…These actions concern respiratory activity, such as increased mitochondrial membrane potential and oxygen consumption [10][11][12], a role that would be in line with metabolism-enhancing properties of property of progesterone, as known from the postovulatory increase in temperature. The mitochondrial PR variant has been shown to be truncated, in which N-terminal domains as well as the DNA-binding domain are absent [10]. Therefore, this PR variant can only act nongenomically.…”