PKCα and PKCδ Activation Regulates Transcriptional Activity and Degradation of Progesterone Receptor in Human Astrocytoma Cells

Abstract

Progesterone regulates cancer cell proliferation and invasion through its receptors (PR-A and PR-B), whose phosphorylation modifies their transcriptional activity and induce their degradation. We identified by in silico analysis a putative residue (Ser400) in PR that might be phosphorylated by protein kinase C (PKC), a family of enzymes involved in the proliferation and infiltration of astrocytomas, the most frequent and aggressive brain tumors. A grade III human astrocytoma-derived cell line was used to study the role of PKC in PR phosphorylation, transcriptional activity, and degradation. Treatment with PKC activator [tetradecanoyl phorbol acetate (TPA)] increased PR phosphorylation in Ser400 after 5 minutes, which in turn induced PR transcriptional activity and its subsequent degradation by the 26S proteasome 3-5 hours after treatment. Silencing or inhibition of PKCα and PKCδ blocked PR phosphorylation and degradation induced by TPA. Both PR isoforms were associated with PKCα and reached the maximum association after 5 minutes of TPA addition. These data correlated with immunnofluorescence assays in which nuclear colocalization of PKCα with PR increased after TPA treatment. We observed a 2-fold increase in cell proliferation after PKC activation with TPA that was reduced with the PR antagonist, RU486. The PR S400A mutant revealed that this residue is essential for PKC-mediated PR phosphorylation and degradation. Our results show a key participation of PKCα and PKCδ in PR regulation and function.

How hormones may modulate human skin pigmentation in melasma: An in vitro perspective

“…However, while Natale et al did not find ER and PR, they found that melanocytes responded to oestrogen via fixation to GPER (G-protein coupled oestrogen receptor) and to progesterone via fixation to PAQR7 (progestin and adipoQ receptor 7), two G protein-coupled receptors. [20] Since various factors such as TPA, PMA, CT, insulin, IGF-1 and EGF [40][41][42][43][44] modulate ER and PR, we hypothesize that melanocytes are able to express ER, GPER, PR and PAQR7 but that their expression in vitro depends on stimulation by exogenous factors.…”

Sex Hormones Regulate Cytoskeletal Proteins Involved in Brain Plasticity

“…Hormone receptor activation can also induce diverse signaling pathways like those mediated by MAPKs, PI3K/Akt, and PKC ( 25 – 27 ), regulate second messenger cascades ( 28 ) or modulate the actions of neurotransmitter receptors ( 29 ). These mechanisms are regulated through PR and ER located in the cytoplasm, nucleus, or plasma membrane ( 30 – 32 ) or through other membrane receptors that have different biochemical and pharmacological properties ( 33 , 34 ).…”

Growth factors and kinases in glioblastoma growth

“…PKCα activates MAPK and MMP, thus increasing infiltration ability [112] ; PKCδ has been linked to radiation-induced apoptosis as well as MMP activation [119,120] ; and PKCε induces proliferation and apoptosis evasion [121] . Moreover, our group has reported that PKCα and PKCδ, through progesterone receptor phosphorylation, induce proliferation and migration [114] . However, further investigation is necessary to completely understand the role of different PKC isoforms in GBM growth as the effects of these kinases tend to be cell-specific and vary according to very particular cell conditions, hence complicating the use of PKC inhibitors in therapy.…”

“…Once triggered, these proteins can activate and interact with other cascades such as MAPK and PI3K, and regulate processes such as proliferation, differentiation, apoptosis, and angiogenesis [110,111] . These events make PKC an important target in cancer, particularly in glioma where its importance has been thoroughly discussed [112][113][114] as PKC shows increased expression and activity in this kind of tumors [115] . There are reports indicating that PKC is important for progesterone-receptor-mediated proliferation in glioma cells, adding to the possible mechanisms of PKC function [114] .…”

“…These events make PKC an important target in cancer, particularly in glioma where its importance has been thoroughly discussed [112][113][114] as PKC shows increased expression and activity in this kind of tumors [115] . There are reports indicating that PKC is important for progesterone-receptor-mediated proliferation in glioma cells, adding to the possible mechanisms of PKC function [114] . Other reports also indicated that PKC induces proliferation, invasion, and metastasis through PI3K, Bad or Cdk7/Cdk2 [116] , mTOR, and Akt activation [117] .…”