Date Published: April 26, 2019
Publisher: Public Library of Science
Author(s): Karlie A. Intlekofer, Kelsey Clements, Haley Woods, Hillary Adams, Alexander Suvorov, Sandra L. Petersen, Partha Mukhopadhyay.
Progesterone membrane receptor component 1 (Pgrmc1) is a cytochrome b5-related protein with wide-ranging functions studied most extensively in non-neural tissues. We previously demonstrated that Pgrmc1 is widely distributed in the brain with highest expression in the limbic system. To determine Pgrmc1 functions in cells of these regions, we compared transcriptomes of control siRNA-treated and Pgrmc1 siRNA-treated N42 hypothalamic cells using whole genome microarrays. Our bioinformatics analyses suggested that Pgrmc1 plays a role in immune functions and likely regulates proinflammatory cytokine signaling. In follow-up studies, we showed that one of these cytokines, TNFα, increased expression of rtp4, ifit3 and gbp4, genes found on microarrays to be among the most highly upregulated by Pgrmc1 depletion. Moreover, either Pgrmc1 depletion or treatment with the Pgrmc1 antagonist, AG-205, increased both basal and TNFα-induced expression of these genes in N42 cells. TNFα had no effect on levels of Rtp4, Ifit3 or Gbp4 mRNAs in mHippoE-18 hippocampal control cells, but Pgrmc1 knock-down dramatically increased basal and TNFα-stimulated expression of these genes. P4 had no effect on gbp4, ifit3 or rtp4 expression or on the ability of Pgrmc1 to inhibit TNFα induction of these genes. However, a majority of the top upstream regulators of Pgrmc1 target genes were related to synthesis or activity of steroids, including P4, that exert neuroprotective effects. In addition, one of the identified Pgrmc1 targets was Nr4a1, an orphan receptor important for the synthesis of most steroidogenic molecules. Our findings indicate that Pgrmc1 may exert neuroprotective effects by suppressing TNFα-induced neuroinflammation and by regulating neurosteroid synthesis.
Progesterone receptor membrane component 1 (Pgrmc1) is an ancient and somewhat enigmatic molecule with a diverse range of functions and multiple intracellular locations. Structurally, it is a 28-kDa protein with an N-terminal extracellular region, a single transmembrane domain and a cytoplasmic region. The cytoplasmic region contains a cytochrome b5-like heme-binding domain that allows interaction with a number of steroidogenic and drug-metabolizing cytochrome P450 enzymes [1–4]. As suggested by its name, Pgrmc1 also contains a high-affinity progesterone (P4) binding site [5–9], most likely within the transmembrane domain and the initial segment of the C terminus  and near the heme-binding site . Finally, the Pgrmc1 molecule contains sites that may allow interaction with SH2- and SH3-domain signaling proteins .
These microarray and bioinformatics findings provide evidence that Pgrmc111 acts independently of P4 to regulate signaling important for neuroimmune functions. Among the genes most highly upregulated by Pgrmc1 depletion were gbp4, ifit3, and rtp4, genes induced by proinflammatory cytokines such as interferons, interleukins and Tnfα [30–33]. Our follow-up studies verified that at least one of these cytokines, TNFα, upregulated expression of gbp4, ifit3, and rtp4 and expression was inhibited by Pgrmc1 in both hypothalamic and hippocampal cell lines. The effect of Pgrmc1 on the expression of these genes was independent of P4, but our analysis of upstream regulators suggests that Pgrmc1 may alter synthesis or signaling of steroids that alter neuroinflammatory signals . Overall, our findings provide new insights into how Pgrmc1 may exert neuroprotective effects.