[The effect of c-Myc on regulating the immune-related ligands in Y subtype small cell lung cancer through histone deacetylase 1].

<b>Objective:</b> To explore the effect and mechanism of c-Myc on regulating the expression of immune-related ligands in Y subtype small-cell lung cancer (SCLC) characterized by high expression of immune-related molecules. <b>Methods:</b> The Y subtype SCLC cell line H196 was randomly divided into the control group, c-Myc inhibitor 10058-F4 group, histone deacetylase 1 (HDAC1) inhibitor pyroxamide group, and 10058-F4 plus pyroxamide group. The co-culture system with NK-92MI cells was used to determine the effect of H196 cells on the function of natural killer (NK) cells. Western Blotting and co-immunoprecipitation assays were used to detect the effect of c-Myc on class Ⅰ HDAC, and flow cytometry was used to detect the regulatory effect of c-Mycon CD47, programmed cell death ligand 1 (PD-L1), and CD155, which are highly expressed immune checkpoints in Y subtype SCLC, and major histocompatibility complex classⅠ-related chains A and (MICA/B), which is a poorly expressed immune-activating ligand in SCLC, and the role of HDAC. Chromatin immunoprecipitation (ChIP) assay and real-time quantitative polymerase chain reaction (RT-qPCR) were used to determine the regulatory mechanism of c-Myc-HDAC1 on MICA/B expression. <b>Results:</b> Inhibition of c-Myc decreased the mortality of H196 cells in the co-culture system and down-regulated the expression of MICA/B. Compared with the NK+H196 group [(42.54±2.47)%], the proportion of cells killed by NK-92MI cells in the NK+H196+10058-F4 group was lower [(28.48±3.38)%, <i>P</i>＜0.001]. The mean fluorescence intensity (MFI) of MICA/B on the cells in the 10058-F4 group (36.40±0.82) was lower than that in the control group (91.23±8.60, <i>P</i>＜0.001). And c-Myc could bind to HDAC1, whose protein level was up-regulated by 10058-F4 while the mRNA level was not. Compared with the cells in the control group (90.10±4.91), the MFI of MICA/B on the cells in the pyroxamide group was significantly increased (145.70±5.86, <i>P</i>＜0.001), and the MFI of MICA/B on the cells in the 10058-F4+pyroxamide group (54.60±2.88) was significantly increased compared with the cells in the 10058-F4 group (35.97±1.60, <i>P</i>＜0.001). The percentage of MICA promoter gene fragments in the c-Myc antibody precipitation group (0.125±0.037) was significantly higher than that in the IgG group (0.000 8±0.000 3, <i>P</i>=0.004). MICB had a similar trend, suggesting that the c-Myc-HDAC1 complex could bind to the promoter region of MICA/B. The MFI of CD47 on the cells in the 10058-F4 group (60.07±0.21) was significantly lower than cells in the control group (70.27±1.37, <i>P</i>＜0.001), but the MFIs of PD-L1 (13.50±0.61) and CD155 (829.70±41.19) were significantly higher than those on the cells in the control group (9.23±0.94, <i>P</i>＜0.01; 496.00±4.36, <i>P</i>＜0.001, respectively). <b>Conclusions:</b> c-Myc may promote the expression of MICA/B and CD47 in Y subtype SCLC cells by binding and inhibiting HDAC1, while it may also be involved in inhibiting the expression of PD-L1 and CD155 in SCLC cells.