Figure - PMC

Skip to main content

An official website of the United States government

Here's how you know

Here's how you know

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

View full-text article in PMC

. 2021 Feb 5;22(4):1626. doi: 10.3390/ijms22041626

Search in PMC
Search in PubMed
View in NLM Catalog
Add to search

© 2021 by the authors.

Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

PMC Copyright notice

PKR, OAS, and IL-24 proteins which are expressed in normal tissues are suppressed in human primary lung cancer tissues. (A) Box-whisker plot showing the transcript levels of PKR, OAS, and IL-24 in TCGA database, respectively. Both AD (adenocarcinoma) tissues (n = 509), SCC (squamous cell carcinoma) tissues (n = 498) and normal tissues (n = 58 for AD group and n = 51 for SCC group) were used for analysis. Data are reported as normalized counts as provided in the TCGA level 3 data (**, p < 0.01). (B) Retrospective staining of patient lung cancer (“C”) and paired normal (“N”) tissues for PKR, OAS, and IL-24 was performed for lung cancer stages I, II, III, and IV. Clinicopathological parameters are shown in Supplementary Figure S6. Inflammatory cell infiltration is indicated with yellow arrows. The protein levels of tumor suppressor markers, PKR and OAS, are dramatically reduced in carcinoma tissues, compared to normal controls. Consistently, anticancer cytokine, IL-24, showed a clear reduction in lung cancer tissues. Scale bar; 100 μm. (C) The corresponding quantitative results of IHC (immunohistochemistry) of PKR, OAS, and IL-24 are shown. (D) A hypothetical model to illustrate PKR activation via interaction with Hiltonol. There are 9 key residues involved in dsRNA-binding [21]. Computational analysis by InterPro (https://www.ebi.ac.uk/interpro/ (accessed on 6 October 2020)) [22] shows that N-terminal of PKR (brown) contains two dsRNA-binding motifs (a.a. 10-76 and a.a. 101-166), whereas C-terminal of PKR (atrovirens) is characterized mainly as protein kinase domain with Ser/Thr kinase active site (a.a. 410–422). The left panel shows that in the absence of Hiltonol, PKR remains in an inactive state, hence leading to tumor progression. The right panel shows that in the presence of Hiltonol (a dsRNA binding agent), PKR homodimerization occurs which leads to autophosphorylation of identified residues. This active form of PKR suppresses tumorigenesis. (E) A hypothetical model of the mechanisms by which Hiltonol mediates killing of lung cancer cells. Hiltonol effectively stimulates the expression of intracellular PKR and OAS [23], which are dsRNA-binding enzymes which mediate cellular antiviral and anti-tumor responses (Figure 4). PKR and OAS RNAi significantly restored cell survival and proliferation upon Hiltonol treatment. Consequentially, Hiltonol plays an immune-modulatory role, which suppresses pro-tumorigenic cytokines: GRO, IL-8, and IL-6, in H292 and H358, and MCP-1 in H1299. In addition, Hiltonol upregulates anti-tumor cytokine, IL-24, in A549 and H292, which also suggests that it contributes to the NSCLC tumorigenic microenvironment.

PKR, OAS, and IL-24 proteins which are expressed in normal tissues are suppressed in human primary lung cancer tissues. (A) Box-whisker plot showing the transcript levels of PKR, OAS, and IL-24 in TCGA database, respectively. Both AD (adenocarcinoma) tissues (n = 509), SCC (squamous cell carcinoma) tissues (n = 498) and normal tissues (n = 58 for AD group and n = 51 for SCC group) were used for analysis. Data are reported as normalized counts as provided in the TCGA level 3 data (**, p < 0.01). (B) Retrospective staining of patient lung cancer (“C”) and paired normal (“N”) tissues for PKR, OAS, and IL-24 was performed for lung cancer stages I, II, III, and IV. Clinicopathological parameters are shown in Supplementary Figure S6. Inflammatory cell infiltration is indicated with yellow arrows. The protein levels of tumor suppressor markers, PKR and OAS, are dramatically reduced in carcinoma tissues, compared to normal controls. Consistently, anticancer cytokine, IL-24, showed a clear reduction in lung cancer tissues. Scale bar; 100 μm. (C) The corresponding quantitative results of IHC (immunohistochemistry) of PKR, OAS, and IL-24 are shown. (D) A hypothetical model to illustrate PKR activation via interaction with Hiltonol. There are 9 key residues involved in dsRNA-binding [21]. Computational analysis by InterPro (https://www.ebi.ac.uk/interpro/ (accessed on 6 October 2020)) [22] shows that N-terminal of PKR (brown) contains two dsRNA-binding motifs (a.a. 10-76 and a.a. 101-166), whereas C-terminal of PKR (atrovirens) is characterized mainly as protein kinase domain with Ser/Thr kinase active site (a.a. 410–422). The left panel shows that in the absence of Hiltonol, PKR remains in an inactive state, hence leading to tumor progression. The right panel shows that in the presence of Hiltonol (a dsRNA binding agent), PKR homodimerization occurs which leads to autophosphorylation of identified residues. This active form of PKR suppresses tumorigenesis. (E) A hypothetical model of the mechanisms by which Hiltonol mediates killing of lung cancer cells. Hiltonol effectively stimulates the expression of intracellular PKR and OAS [23], which are dsRNA-binding enzymes which mediate cellular antiviral and anti-tumor responses (Figure 4). PKR and OAS RNAi significantly restored cell survival and proliferation upon Hiltonol treatment. Consequentially, Hiltonol plays an immune-modulatory role, which suppresses pro-tumorigenic cytokines: GRO, IL-8, and IL-6, in H292 and H358, and MCP-1 in H1299. In addition, Hiltonol upregulates anti-tumor cytokine, IL-24, in A549 and H292, which also suggests that it contributes to the NSCLC tumorigenic microenvironment.