Tumor-associated macrophages confer colorectal cancer 5-fluorouracil resistance by promoting MRP1 membrane translocation via an intercellular CXCL17/CXCL22-CCR4-ATF6-GRP78 axis

Chemotherapy represents a major type of clinical treatment against colorectal cancer (CRC). Aberrant drug efflux mediated by transporters acts as a key approach for tumor cells to acquire chemotherapy resistance. Increasing evidence implies that tumor-associated macrophages (TAMs) play a pivotal role in both tumorigenesis and drug resistance. Nevertheless, the specific mechanism through which TAMs regulate drug efflux remains elusive. Here, we discovered that TAMs endow CRC cells with resistance to 5-fluorouracil (5-FU) treatment via a cell-cell interaction-mediated MRP1-dependent drug efflux process. Mechanistically, TAM-secreted C-C motif chemokine ligand 17 (CCL17) and CCL22, via membrane receptor CCR4, activated the PI3K/AKT pathway in CRC tumor cells. Specifically, phosphorylation of AKT inactivated IP3R and induced calcium aggregation in the ER, resulting in the activation of ATF6 and upregulation of GRP78. Accordingly, excessive GRP78 can interact with MRP1 and promote its translocation to the cell membrane, causing TAM-induced 5-FU efflux. Taken together, our results demonstrated that TAMs promote CRC chemotherapy resistance via elevating the expression of GRP78 to promote the membrane translocation of MRP1 and drug efflux, providing direct proof for TAM-induced drug resistance.

Salvianolic acid A attenuates inflammation-mediated atherosclerosis by suppressing GRP78 secretion of endothelial cells

ETHNOPHARMACOLOGICAL RELEVANCE

Salvianolic acid A (SAA) is the main active component of the classic anti-atherosclerotic drug Salvia miltiorrhiza Bunge. Inflammation-induced infiltration of monocyte/macrophages into the vascular wall is the initiating step in atherogenesis, and targeted blocking of this step may provide a promising avenue for the precise treatment of atherosclerosis. However, the effect of salvianolic acid A on macrophages is still unknown.

AIM OF THE STUDY

To evaluate the effect of SAA on macrophage infiltration and the underlying mechanism of SAA against atherosclerosis.

MATERIALS AND METHODS

Vascular endothelial cells were stimulated with lipopolysaccharide (LPS) to simulate the inflammatory environment, and its effect on monocyte/macrophages was evaluated. Mass spectrometry was used to identify the proteins that play a key role and further validated them. LncRNA sequencing, western blot analysis, RNA immunoprecipitation, and RNA pulldown were used to elucidate the mechanism of SAA against atherosclerosis. Finally, ApoE^-/- mice were fed a high-fat diet to creat an in vivo atherosclerosis model. Secretory GRP78 content, lipid levels, plaque area, macrophage infiltration, and degree of inflammation were assessed by standard assays after 16 weeks of intragastric administration of SAA or biweekly tail vein injections of GRP78 antibody.

RESULTS

After LPS stimulation, the increased secretion of GRP78 recruits circulating monocyte/macrophages and drives monocyte/macrophage adhesion and invasion into the vascular intima to promote atherosclerosis progression. Interestingly, SAA exerts anti-atherosclerosis effects by inhibiting the secretion of GRP78. Further mechanistic studies indicated that SAA upregulates the expression of lncRNA NR2F2-AS1, which reverses the abnormal localization of the KDEL receptor (KDELR) caused by inflammation. It promotes the homing of GRP78 from the Golgi apparatus to the endoplasmic reticulum rather than secreting outside the cell.

CONCLUSION

SAA alleviates atherosclerosis by inhibiting GRP78 secretion via the lncRNA NR2F2-AS1-KDELR axis. The findings not only provide a new direction for the precise therapy of atherosclerosis based on secretory GRP78 but also elucidate the pharmacological mechanism of SAA against atherosclerosis, putting the foundation for further development and clinical application of SAA drugs.

Tumor-secreted GRP78 induces M2 polarization of macrophages by promoting lipid catabolism

Macrophages in hypoxic regions of advanced colorectal tumors often exhibit M2-type features, but prefer oxygen-consuming lipid catabolism, which is contradictory in oxygen demand and supply. In this study, the results from bioinformatics analysis and intestinal lesions immunohistochemistry of 40 colorectal cancer patients illustrated that glucose-regulatory protein 78 (GRP78) was positively correlated with M2 macrophages. Furthermore, tumor-secreted GRP78 could enter macrophages and polarize them to M2-type. Mechanistically, entered GRP78 located in lipid droplets of macrophages, and elevated protein stabilization of adipose triglyceride lipase ATGL by interacting with it to inhibit its ubiquitination. Increased ATGL promoted the hydrolysis of triglycerides and the production of arachidonic acid (ARA) and docosahexaenoic acid (DHA). Excessive ARA and DHA interacted with PPARγ to encourage its activation, which mediated the M2 polarization of macrophages. In summary, our study showed that secreted GRP78 in the tumor hypoxic microenvironment mediated the domestication of tumor cells to macrophages and maintained tumor immunosuppressive microenvironment by promoting lipolysis, and the lipid catabolism not only provides energy for macrophages but also plays an important role in maintenance of immunosuppressive properties.

Ferulic Acid and P-Coumaric Acid Synergistically Attenuate Non-Alcoholic Fatty Liver Disease through HDAC1/PPARG-Mediated Free Fatty Acid Uptake

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease and has become a growing public health concern worldwide. Polyphenols may improve high-fat diet (HFD)-related NAFLD. Our previous study found that ferulic acid (FA) and p-coumaric acid (p-CA) were the polyphenols with the highest content in foxtail millet. In this study, we investigated the mechanism underlying the impact of ferulic acid and p-coumaric acid (FA/p-CA) on non-alcoholic fatty liver (NAFLD). The association of FA and p-CA with fatty liver was first analyzed by network pharmacology. Synergistic ameliorating of NAFLD by FA and p-CA was verified in oleic acid (OA) and palmitic acid (PA) (FFA)-treated hepatocytes. Meanwhile, FA/p-CA suppressed final body weight and TG content and improved liver dysfunction in HFD-induced NAFLD mice. Mechanistically, our data indicated that FA and p-CA bind to histone deacetylase 1 (HDAC1) to inhibit its expression. The results showed that peroxisome proliferator activated receptor gamma (PPARG), which is positively related to HDAC1, was inhibited by FA/p-CA, and further suppressed fatty acid binding protein (FABP) and fatty acid translocase (CD36). It suggests that FA/p-CA ameliorate NAFLD by inhibiting free fatty acid uptake via the HDAC1/PPARG axis, which may provide potential dietary supplements and drugs for prevention of NAFLD.

Tumor-secreted GRP78 facilitates the migration of macrophages into tumors by promoting cytoskeleton remodeling

Glucose-regulated protein 78 (GRP78), an important molecular chaperone in the endoplasmic reticulum, is often over-expressed in the central region of advanced tumor and acts as a promoter of tumor progression. As main immune cells in the tumor microenvironment, infiltration of abundant macrophages into advanced tumor further facilitates growth of tumor. Although has potential association between GRP78 and infiltration of macrophages, its underlying mechanisms are poorly understood. Here, we report that secreted GRP78 facilitates recruitment of macrophages into tumors both in vitro and in vivo. Further studies reveal that secreted GRP78 transports into macrophages and bound to intracellular Ca²⁺, which lead to uneven distribution of Ca²⁺ and subsequent polarization of macrophages. The polarization of macrophages activates expression of microRNA-200b-3p. By directly targeting RhoGDI, miR-200b-3p stimulates the activity of RhoGTPase and ultimately leads to the distribution of GTP-Rac1 and GTP-Cdc42 in front protrusion and GTP-RhoA in rear contraction, which further results in migration of macrophages in a certain direction. Our results reveal a novel function of GRP78 to promote the recruitment of macrophages to tumor and provide a potential therapeutic target for malignancies.

(-)-Epigallocatechin Gallate (EGCG) Enhances the Sensitivity of Colorectal Cancer Cells to 5-FU by Inhibiting GRP78/NF-κB/miR-155-5p/MDR1 Pathway

Green tea accounts for approximately 20% of the world's total tea yield. (-)-Epigallocatechin gallate (EGCG) is an active catechin in green tea, which suppresses tumor growth and enhances drug sensitivity in various cancers, but the molecular mechanism is still unclear. Chemotherapy drugs, such as 5-fluorouracil (5-FU), are a common strategy for clinical treatment of cancer patients; however, the lower response rate caused by prolonged use becomes the main reason for tumor recurrence. Therefore, discovering a safe and effective chemo-sensitizer is an urgent task required to be solved. Here, we report that EGCG reinforces the sensitivity of colon cancer cells to 5-FU, and the IC₅₀ values of 5-FU is decreased from 40 ± 4.2 μM to 5 ± 0.36 μM in one human colon carcinoma cell line-HCT-116, and from 150 ± 6.4 μM to 11 ± 0.96 μM in the other human colon carcinoma cell line-DLD1 when these cells are cotreated with 50 μM EGCG. Consistently, compared to 5-FU or EGCG treatment alone, the combination of both significantly promotes cancer cell apoptosis and DNA damage. Further mechanism research reveals that treatment of colorectal cancer (CRC) with 50 μM EGCG inhibits GRP78 expression, activates the NF-κB (2.55 ± 0.05-fold for HCT-116 and 2.27 ± 0.08-fold for DLD1) pathway, and enhances miR-155-5p (2.12 ± 0.02-fold for HCT-116 and 2.01 ± 0.01-fold for DLD1) level. The elevated miR-155-5p strongly suppresses target gene MDR1 expression, which blocks the efflux of 5-FU. The accumulation of 5-FU resulted in caspase-3 and PARP activation, Bcl-2 reduction, and Bad increase, which ultimately lead to cancer cell apoptosis. Overall, our data show that EGCG may be act as a novel chemo-sensitizer, and the GRP78/NF-κB/miR-155-5p/MDR1 pathway plays a vital role in EGCG enhancing the sensitivity of colorectal cancer to 5-FU.

Ajuba receptor mediates the internalization of tumor-secreted GRP78 into macrophages through different endocytosis pathways

Glucose-regulated protein 78 (GRP78), an ER chaperone, is overexpressed in cancer cells. Solid tumor cells can secrete GRP78 that can promote tumor angiogenesis, differentiation of bone marrow-derived mesenchymal stem cells, tumor cell proliferation and polarization of tumor-associated macrophages. However, the mechanism by which GRP78 functions as a tumor promoter either by staying on the membrane to stimulate intracellular signals or directly entering into cytosolic remains unknown. Here, we reported that an endotoxin-free His-GRP78 protein was purified in vitro that simulates original secreted GRP78. Through analyzing GRP78 concentration in serum samples from 32 colon cancer patients, 40 nM His-GRP78 was selected as an optimized dose to treat cells. Biochemical analysis revealed that secreted GRP78 was able to enter into RAW264.7 and THP-1 cells directly rather than stay on the plasma membrane to transfer signals. Further studies showed that GRP78 internalization was endocytosis-dependent, and both phagocytosis and clathrin, caveolin-1 and micropinocytosis-mediated endocytosis pathways contributed to internalization of secreted GRP78 into cells. Mechanistically, Ajuba is able to interact with GRP78. Ablation of Ajuba suppressed the internalization of secreted GRP78 into cells, indicating that Ajuba was responsible for internalization of secreted GRP78 into RAW264.7. Furthermore, we observed that internalized GRP78 could entered into the mitochondrion and endoplasmic reticulum, which provided a suitable place and enough time for GRP78 to function in molecular and cellular processes. Together, these results reveal a novel mechanism by which secreted GRP78 internalizes into macrophages in the tumor microenvironment, which provides a potential target for drug development.

Berberine-induced autophagic cell death by elevating GRP78 levels in cancer cells

Berberine, an isoquinoline alkaloid extracted from Coptidis Rhizoma, has been shown to induce cancer cell autophagic death. Glucose regulated protein 78 (GRP78) is associated with stress-induced autophagy. However, the related mechanisms between berberine-induced cancer cell autophagy and GRP78 remain to be elucidated. Here, we report that berberine can induce autophagic cancer cell death by elevating levels of GRP78. These results further demonstrated that berberine enhanced GRP78 by suppression of ubiquitination / proteasomal degradation of GRP78 and activation of ATF6. Moreover, fluorescence spectrum assay revealed that berberine could bind to GRP78 and form complexes. Finally, co-IP analysis showed that the ability of GRP78 to bind to VPS34 was increased with berberine treatment. Taken together, our results suggest that berberine induces autophagic cancer cell death via enhancing GRP78 levels and the ability of GRP78 to bind to VPS34.

Design, purification and assessment of GRP78 binding peptide-linked Subunit A of Subtilase cytotoxic for targeting cancer cells

BACKGROUND

Targeted therapies for cancer, especially the malignant cancer, are always restricted by the deficiency of tumor-specific drug delivery methods. Subtilase cytotoxic is a virulent cytotoxin, and the subunit A (SubA) of it is able to destroy the structure of glucose-regulated protein 78 (GRP78) to induce cell apoptosis, and to be expected as anti-cancer drugs, however, the ubiquitous receptor of subunit B of Subtilase cytotoxic (SubB) restricts its application on cancer therapy.

RESULTS

The present study constructed and expressed a fusion protein of GBP-SubA in E. coli Rosetta (DE3) system, in which the subunit B of Subtilase cytotoxic was replaced by GRP78 binding peptide (GBP). The fusion protein was expressed in inclusion body form. Subsequently, the denaturation/renaturation process and Ni-column purification were performed. Our data indicated the purified GBP-SubA could bind GRP78 existed on cancer cell surface specifically, internalize into cells to inactivate intracellular GRP78 and induce apoptosis. Moreover, the apoptosis induction effect of GBP-SubA was enhanced obviously along with the increased cancer cell surface GBP78.

CONCLUSIONS

It indicates that the recombinant GBP-SubA possesses the dual functions of GBP and SubA to induce cancer cell apoptosis specifically, revealing that GBP-SubA holds important implications for developing as an anti-cancer peptide drug. A schematic representation of the construction and function of GBP-SubA.