that hif - 1 downregulates the antigen presenting mhc class i molecules is an important strategy for cancer to evade immune attack, because only in combination with mhc class i on the target cells, can tumor antigenic peptides be recognized by cd8 + ctl with the subsequent destruction of the target cells. theoretically, inhibition of hif - 1 may upregulate the expression of mhc class i on cancer cells. this study demonstrated that 25 μg / ml endostar inhibited expression of hif - 1 with the upregulation of mhc class i α - heavy chain and β2 m light chain in a549 and nci - h1299 lung cancer cells, suggesting the potential for endostar to facilitate cancer immunotherap y. experimental evidence, however, is required and further research with experimental evidence remains to be performed in the future to confirm the possible suppression of immune evasion tactic with endostar treatment. other limitations such as lack of an in vivo tumor model and further validation using flow cytometry remain to be supplementarily performed in the future. the mechanism of mhc class i regulation involves the innate immune molecule nlr family card domain containing 5 ( nlrc5 ), which is a member of recently discovered nlrs - like receptor family of the highly conserved one. 46 nlrc5 is an mhc class i gene transactivation factor which induces the mhc class i gene transcription and subsequently activates antigen presentation process. 47, 48 nlrc5 is transcriptionally regulated in jak2 / stat3 signaling - dependent pathway. 49 this study demonstrated that some concentrations of endostar decreased the relative levels of stat3 and pstat3 in a549 lung cancer cells with statistical significance, which is in line with the role of jak2 / stat3 pathway in regulation of mhc class i via nlrc5, suggesting the underlying mechanism of mhc class i upregulation involving jak2 / stat3 signaling pathway. conclusions endostar ( 25 μg / ml ) inhibited the expression of hif - 1 with the upregulation of mhc class i α - heavy chain and β2 m light chain in a549 and nci - h1299 lung cancer cells, which showed the potential for endostar to facilitate cancer immunotherap y. it is needed for future studies that are warranted to confirm the role of endostar treatment. introduction hepatocellular carcinoma ( hcc ) is an exceedingly fatal malignancies, with mortalities that approximate the incidence rates worldwide [ 1 ]. hcc is usually diag nosed at advanced stages owing to late symptom manifestations with limited therapeutic options, leading to ineffective intervention and poor prognosis [ 2 ]. an increasing number of studies have focused on the progression, pathological features, and prognosis of liver cancer [ 3 – 5 ]. hcc epidemiology is rapidly evolving, one of the most common causes is non - alcoholic fatty liver disease [ 6 ], further proving that lipid metabolism plays a crucial role in hcc occurrence. therefore, the identification of novel therapeutic targets is urgently needed to improve the treatment of patients with hcc [ 7 ]. phosphatidylethanolamine ( pe ), also known as cephalin, is the most abundant lipid in the cytoplasmic layer of cell membranes and is involved in cellular processes such as membrane fusion [ 8 ], autophagy and apoptosis [ 9 – 11 ]. for eukaryotic pe in vivo, two main synthetic pathways exist [ 12 ]: including the kennedy pathway of cdp - ethanolamine ( cdp - etn ) and mitochondrial phosphatidylserine decarboxylation pathway [ 13 ]. phosphatidylethanolamine cytidyltransferase 2 ( pcyt2 ) is the rate - limiting enzyme of the cdp - etn pathway. previous studies have shown that pcyt2 is highly specific, and is present only in the rough endoplasmic reticulum of eukaryotes [ 14 ]. p - eth is then catalyzed by pcyt2 to form cdp - etn, leading to pe synthesis [ 15 ]. generally, pcyt2 expression is reduced in various epithelial - derived cancer cell lines compared to normal cells [ 16, 17 ]. compared epithelial - derived cancer cell lines pcyt2 activity with that of breast epithelial cells mcf - 10a showed that its pcyt2 activity was inhibited in breast cancer cells ( mcf - 7 ) [ 16 ]. pcyt2 expression was significantly reduced in invasive human metastatic colon cancer cells compared to that in primary tumor cells [ 17 ], and previous studies have shown that pcyt2 knockdown under nutrient - rich conditions significantly facilitated the proliferation of hela and t98g cells and promoted in vivo tumor growth. the inhibition of pcyt2 increases p - etn levels in cancer cells and stimulates tumor growth [ 18 ]. however, in organoid models, pcyt2 knockdown inhibits cell growth [ 19 ]. despite these findings, no evidence exists that suggests that pcyt2 expression is associated with hcc occurrence and development. this study aimed to investigate the role of pcyt2 in human hepatocellular carcinoma cells ( hepg2 ) by inhibiting their proliferation, invasion, and migration abilities and promoting cell apoptosis. materials and methods cell viability analysis hepg2 cells were seeded into 96 - well plates and incubated with a cell counting kit ( cck - 8 ) solution for 40 min at 37°c. absorbance was measured at 450 nm using a spectra max m5 microplate spectrophotometer to detect cell viability. invasion experiment dilute the matrigel with basal medium ( 1: 8 ), lay it flat on a transwell membrane, and incubate at 37°c for 4 h. the subsequent experimental steps were identical to those used for the migration assay, including cell culture, paraformaldehyde fixation and 0. 1 % crystal violet staining. animal experiments five - week - old balb / c female nude mice were purchased from jiangsu jicui pharmaceutical biotechnology co, passed spf level training and assessment, and were routinely reared using standard spf conditions. pcyt2 overexpressed hepg2 cells and control cells were subcutaneously injected into the left and right sides of the nude mice ( approximately 1 × 107 cells on each side, n = 6 tumors in each group ). following 20 – 25 d, the tumors achieved a certain size and the micewere anesthetized with isopentane and sacrificed; the tumors were collected for follow - up evaluation. the animal experiments were approved by the animal ethics committee of anhui medical university and conducted in accordance with the guidelines for the care and use of laboratory animals. statistical analysis data were analyzed using graphpad prism software ( version 8. 0 ), and the results were expressed as mean ± standard deviation ( sd ). t - test was performed to determine the significant of differences between two groups. a one - way analysis of variance was used for comparison across groups. statistical significance was set at p * * * results * * * discussion pcyt2 is a rate - limiting enzyme in pe synthesis that is commonly used in the study of obesity - related diseases, such as non - alcoholic fatty liver disease and type 2 diabetes [ 12, 20 – 22 ]. recently, interest in the role of pcyt2 in cancer has been growing [ 18, 23, 24 ]. previous studies show that pcyt2 has different roles in various cancers and cancer settings. for instance, in metastatic colorectal cancer ( crc ), pcyt2 is significantly downregulated and functions as a tumor metastasis inhibitor [ 25 ]. in human breast cancer cells ( mcf - 7 ), the level of pcyt2 in cancer cells is elevated in response to the stressful environment [ 26 ]. our findings show that pcyt2 expression is abnormally downregulated in hepg2 cells, which is consistent with that of previous studies where in pcyt2 expression was downregulated in mcf - 7 and invasive human metastatic crc [ 16, 17 ]. although pcyt2 regulates several human cancers [ 18, 19, 23 ], its role in hcc cells remains unknown. based on the literature and our findings, pcyt2 in human cancers appears to have a consistent expression profile in human cancers, irrespective of tumor origin or location [ 27 ].