Differential regulation of apoptosis and senescence by the miR-449 family microRNAs and its implications in tumor microenvironments of NSCLC

[[abstract]]MicroRNAs (miRNAs) play important roles in various biologic processes, and aberrant miRNA expression is one of the mechanisms of tumorigenesis. Previous studies indicate that oncogenic HPV infection interrupts the expression of tumor-suppressive miR-34a and contributes to the development of cervical cancer. In addition, the traditional Chinese medicine Gynostemma pentaphyllum (Thunb.) Makino may exert its pharmacologic effects through modifying the gut microbiota by regulating hepatic miR-34a expression. MiR-449 miRs are members of the tumor suppressor miR-34 family and are evolutionarily conserved. In this study, we demonstrated that, in lung cancer cells, ectopic expression of miR-449 family, including miR-449a, miR-449b, and miR-449c, decreased the levels of several G1 phase proteins including cyclin D1, cyclin D3, CDK4, and CDK6 via directly targeting their mRNA’s 3’-UTR. We also observed a differential induction of apoptosis vs. senescence by the miR-449 cluster. While miR-449a and miR-449c induced senescence, miR-449b induced apoptosis and sensitized cancer cells to apoptotic stimuli, such as serum deprivation. Interestingly, among this cluster miRNAs, only miR-449a could induce significant senescence-associated secretory phenotype (SASP), e.g., expression of IL-8, IL-6, IL-1b, and TNF-alpha. Moreover, we also found that miR-449a increased NF-kB phosphorylation at S276, but not phosphorylation site of S536, and promoted the expression of IL-8 mRNA. In this regard, the gut microbiota has been indicated to induce proinflammatory cytokines such as IL-8 to influence the outcomes of cancer patients. In addition to MRX34 (a miR-34a mimic) used in clinical trials, miR-449 family may also potentially become a new therapeutic candidate for NSCLC and other solid tumors’ treatmen