Immunogenicity of mammary tumor cells can be induced by shikonin via direct binding-interference with hnRNPA1

Abstract

Immunogenic cell death (ICD) of tumor cells occurs via various pathways that activate immune cell systems against cancer. Previous studies have demonstrated that shikonin (SK), a plant secondary metabolite, can confer strong pharmacological activities that activate ICD and strong immunogenicity of tumor cells. However, the exact hierarchical regulatory mechanisms including the molecular targets of SK-activated immunogenicity are still unknown. Here, the heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) was revealed to serve as a specific protein target for SK. This binding plays a key role in SK-stimulated ICD activity and the suppression of post-transcriptional mRNA processing, including nuclear export activity of newly synthesized mRNAs in mammary carcinoma cells in vitro. Moreover, it also mechanistically mediates the anti-metastatic effect of a tumor cell lysate (TCL) vaccine, which can be readily generated from SK-treated 4T1 tumor cells (SK-TCL), and the derived tumor-immunogenicity of SK-TCL-treated dendritic cells in vivo. Together, the identification of hnRNPA1 as the intracellular molecular target provides compelling pharmacology-based knowledge for the potential clinical use of SK-induced immunogenicity. In addition, SK may also serve as a potent suppressor that interferes with specific post-transcriptional activities, a mechanism which may be useful for exploitation in cancer therapeutics.

Naturally occurring anti-cancer compounds: shining from Chinese herbal medicine

“…It can enhance the proliferation of NK cells and its cytotoxicity to human colorectal cancer Caco-2 cells by regulating ERK1/2 and Akt expressions [623]. It can also bind directly to heterogeneous nuclear ribonucleoprotein A1 to induce immunogenic cell death in human breast cancer MDA-MB-231 cells [624]. Shikonin is also reported to be used as an immunotherapy modifier in cell-based cancer vaccine systems, suggesting its potential application in cancer immunotherapy [625].…”

Molecular basis of shikonin-induced immunogenic cell death: insights for developing cancer therapeutics

“…In addition, hnRNPA1 has been shown to play an important role in control of specific splicing activity of tyrosine kinase receptor (Ron), and can thus further promote the MET activity [33] . Taking these findings together, we contemplate that SK-induced EMT and the related changes in microRNA expression in vivo may also reflect the dysfunction of hnRNPA1 activity [7] . Therefore, the application of SK in promoting tissue wound-healing activity after clinical resection of tumors in cancer patients may constitute another avenue of research to aid the recovery of cancer patients.…”

“…Recently, a molecular target of SK, namely heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1), was identified to play a key role in SK-induced ICD in mammary tumor cells [7] . Specifically, hnRNPA1 was shown to act as an important substrate of GzmA that can impair the nuclear export activity of newly synthesized RNA, and this resulted in a specific type of immune-mediated programmed cell death [8] .…”

“…These results indicate that SK may exhibit both pro-and anti-inflammatory activities at the tissue/organ levels. The identification of hnRNPA1 [7] may provide a plausible mechanistic explanation for this seemingly contradictory "Yin vs. Yang" regulation, and the diverse effects of SK on epithelial tissues. We suggest that by targeting hnRNPA1 activity via binding with SK the splicing and nuclear export activities of specific inflammation-related genes may be efficiently, but transiently, suppressed, and this highly temporal action may result in an interruption of the acute "cytokine storm", effecting timely control of the "resolution" of inflammation activities.…”

“…Among various ICD inducers, SK can effectively induce ICD activity of tumor cells and increase the expression of DAMPs in the resultant tumor cell lysate (TCL), which could then be used to stimulate strong anti-tumor activity in a DC-based cancer vaccine approach [15][16][17] . Recently, the targeting of hnRNPA1 by SK has been proven to play a key role in SK-induced ICD in mammary tumor cells and the derived anti-metastatic activities of vaccinated DCs [7] . Moreover, three specific ICD proteins were shown to exhibit distinguishable or comprehensive activities in activating DCs (Figure 2).…”