Hypoxia-Induced Expression of miR-424, miR-155, CD47, and PD-L1 in a Gastric Cancer Cell Line (MKN-45).

Background: Hypoxia (pO2 < 5-10 mmHg) is a critical feature of the tumor environment that causes genetic and epigenetic changes. This study aimed to evaluate the effect of hypoxia on the expression of immune checkpoint genes (CD39, CD47, and PD-L1) and their regulatory microRNAs (miRNAs; miR-155, miR-424, miR-133, miR-142) in the gastric cancer cell line MKN-45. Methods: MKN-45 cells were cultured under standard conditions and treated with 25 µM of CoCl2 for 24 hours to induce hypoxia. In the next step, the mRNA expression levels of CD39, CD47, PD-L1, miR-155, miR-424, miR-133, and miR-142 were analyzed in the MKN-45 cells under hypoxia versus normoxia. Also, the protein levels of PD-L1 were assessed using Western blot analysis. Results: Hypoxia was confirmed by increased hypoxia-inducible factor 1α expression in MKN-45 cells treated with CoCl2. Under hypoxic conditions, CD47 and PD-L1, as well as miR-424 and miR-155, showed significantly higher expression levels in hypoxia compared to normoxia. Also, Western blot analysis corroborated the increased PD-L1 expression in hypoxia. However, CD39, miR-133, and miR-142 did not show statistical differences between the two conditions. Conclusion: Our in vitro findings indicate that CD47 expression under hypoxic conditions may be influenced by other miRNAs (miR-424) or the duration of hypoxia. Also, the relationship between PD-L1 and miR-155 expression suggests that PD-L1 can be regulated by other miRNAs and that hypoxia enhances its expression. These outcomes indicate that targeting hypoxia in the tumor microenvironment may improve cancer immunotherapy strategies.