Baicalin Targets HSP70/90 to Regulate PKR/PI3K/AKT/eNOS Signaling Pathways.

Baicalin is a major active ingredient of traditional Chinese medicine Scutellaria baicalensis, and has been shown to have antiviral, anti-inflammatory, and antitumor activities. However, the protein targets of baicalin have remained unclear. Herein, a chemical proteomics strategy was developed by combining baicalin-functionalized magnetic nanoparticles (BCL-N3@MNPs) and quantitative mass spectrometry to identify the target proteins of baicalin. Bioinformatics analysis with the use of Gene Ontology, STRING and Ingenuity Pathway Analysis, was performed to annotate the biological functions and the associated signaling pathways of the baicalin targeting proteins. Fourteen proteins in human embryonic kidney cells were identified to interact with baicalin with various binding affinities. Bioinformatics analysis revealed these proteins are mainly ATP-binding and/or ATPase activity proteins, such as CKB, HSP86, HSP70-1, HSP90, ATPSF1ß and ACTG1, and highly associated with the regulation of the role of PKR in interferon induction and the antiviral response signaling pathway (P = 10-6), PI3K/AKT signaling pathway (P = 10-5) and eNOS signaling pathway (P = 10-4). The results show that baicalin exerts multiply pharmacological functions, such as antiviral, anti-inflammatory, antitumor, and antioxidant functions, through regulating the PKR and PI3K/AKT/eNOS signaling pathways by targeting ATP-binding and ATPase activity proteins. These findings provide a fundamental insight into further studies on the mechanism of action of baicalin.

nc886, a non-coding RNA, inhibits UVB-induced MMP-9 and COX-2 expression via the PKR pathway in human keratinocytes.

nc886, a long non-coding RNA (ncRNA) of 101 nucleotides in length, is known as a vault RNA or microRNA precursor. Despite the recent discovery that ncRNAs in the nucleus play a crucial role in regulating chromosomal transformation and transcription, only a few studies have focused on the function of ncRNAs in the cytoplasm, such as nc886. Several studies have investigated the function of nc886 as a suppressor of carcinogenesis and inflammation in different cancer cell types; however, its role in the skin has yet to be clearly elucidated. The two RNA binding sites for protein kinase RNA-activated (PKR) are located in the central region of the stable structure of nc886, which competes with other double-stranded RNA species. Successful binding results in decreased PKR activity. Among changes in skin cells induced by ultraviolet B (UVB) radiation, nc886 expression decreases, whereas PKR phosphorylation via mitogen-activated protein kinases (MAPKs) increases. Reduced nc886 expression leads to uncontrolled PKR activity and increases in the expression of inflammatory cytokines, matrix metalloproteinase-9 (MMP-9), type IV collagenase, and cyclooxygenase (COX-2), which ultimately accelerate inflammatory responses and skin aging. The present study investigated the regulatory mechanism associated with PKR activity and nc886-PKR binding in skin cell aging and inflammation. These results suggest a role for nc886 in controlling photoaging and inflammation in skin cells.

Icariin alleviates the injury of Sertoli cell junction function by upregulating PKR pathway via ERα/c-fos signaling in aged mice.

ETHNOPHARMACOLOGICAL RELEVENACE: Sertoli cells are vital to maintain spermatogenesis and their function decline during aging. Epimedium has the effects of tonifying kidney-yang, strengthening bones and muscles, and expelling wind and dampness, and is commonly used in the treatment of kidney-yang deficiency, impotence and spermatorrhea. Icariin is the main active ingredients from Epimedium exhibiting delaying aging effects and improving male reproductive dysfunction. Whereas, it remains poorly understood how icariin alleviates age-associated decline in testicular function by protecting against the damage of junction function of Sertoli cells. AIM OF THE STUDY: This study aimed to evaluate the improvement effect of icariin on Sertoli cell junction function damage and explore the underlying mechanisms. MATERIALS AND METHODS: Male C57BL/6 mice and mouse Sertoli cell line TM4 cells were utilized to assess the improvement effect of icariin on aging-associated Sertoli cell junction function injury. H&E staining, transmission electron microscopy, qPCR, Western blot, molecular docking, siRNA transfection, and immunofluorescence were performed in this study. RESULTS: Dietary administration of icariin remarkly attenuated age-associated deterioration in spermatogenic function as evidenced by elevated testicular weight and index, sperm concentration and sperm viability. In addition, icariin protected Sertoli cell junction function from age-associated damage as proven by increased Sertoli cell numbers, improved tight junction ultrastructure, and upregulated junction-related proteins (ZO-1, Occludin and ß-Catenin). Moreover, icariin significantly upregulated ERα/c-fos signaling and PKR pathway in testicular Sertoli cells. Similarly, in vitro studies revealed that deletion of ERα, c-fos or PKR abolished the improvement effects of icariin on Sertoli cell junction function damage. CONCLUSIONS: Icariin effectively mitigates age-associated decline in testicular function by diminished Sertoli cell junction function damage through upregulating PKR pathway via ERα/c-fos signaling. Therefore, attenuating Sertoli cell junction function injury by the upregulation of PKR pathway via ERα/c-fos signaling probably indicates an effective target for the prevention and treatment of testicular spermatogenic function with aging.

Porcine circovirus type 2 exploits cap to inhibit PKR activation through interaction with Hsp40.

Porcine circovirus type 2 is the main pathogen of porcine circovirus disease, which has caused enormous economic losses to the pig industry worldwide. The PKR signaling pathway is important for the cellular antiviral response, but its role in the process of PCV2 infection is unknown. In this study, we first found that dsRNA was produced and that PKR was activated in PCV2 infection. However, interestingly, the activation of PKR was inhibited when the Cap protein was exogenously expressed in PAMs, and this inhibition was reversed by the expression of DNAJC7. The interaction between Cap and DNAJC7 was confirmed by laser confocal microscopy, coimmunoprecipitation and GST pull-down, and it was found that PCV2 infection or the expression of Cap protein could induce DNAJC7 to migrate to the nucleus and release P58IPK, an inhibitor of PKR activation. Downregulating the expression of DNAJC7 by a specific inhibitor or recombinant lentivirus-mediated shRNA, inhibited the replication of the PCV2 genome and the production of virions, which was consistent with the increase of DNAJC7 expression in multiple tissues of weaned piglets infected with PCV2. These data indicate that although PKR was activated by PCV2 infection, the activation was inhibited by Cap through an interaction with DNAJC7. These results help to understand the molecular mechanism of immune escape after PCV2 infection.