Background: We previously reported an inverse relationship between B cell-specific Moloney murine leukemia virus integration site 1 (Bmi-1) and Raf kinase inhibitory protein (RKIP), which is associated with the prognosis of gastric cancer (GC). In this study, we further explored the microRNA (miRNA) regulatory mechanism between Bmi-1 and RKIP. Methods: Microarray analysis was first carried out to identify miRNA profiles that were differentially expressed in cells overexpressing Bmi-1. Then, miRNAs that could regulate RKIP were identified. Quantitative real-time PCR (qRT-PCR) and Western blotting were performed to measure the expression of Bmi-1, miR-155, miR-27a and RKIP. RKIP was confirmed as a target of miR-27a and miR-155 through luciferase reporter assays, qRT-PCR and Western blotting. The effects of the Bmi-1/miR-27a/RKIP and Bmi-1/miR-155/RKIP axes on tumor growth, proliferation, migration, invasion, colony-formation ability, metastasis and chemoresistance were investigated both in vitro and in vivo. Results: The downregulation of RKIP by Bmi-1 occurred at the protein but not mRNA level. This indicates probable posttranscriptional regulation. miRNA expression profiles of cells with ectopic expression of Bmi-1 were analyzed and compared to those of control cells by microarray analysis. A total of 51 upregulated and 72 downregulated miRNAs were identified. Based on publicly available algorithms, miR-27a and miR-155 were predicted, selected and demonstrated to target RKIP. Bmi-1, miR-27a and miR-155 are elevated in human GC and associated with poor prognosis of GC, while RKIP is expressed at lower levels in GC and correlated with good prognosis. Then, in vitro tests shown that in addition to regulating RKIP expression via miR-27a and miR-155, Bmi-1 was also able to regulate the migration, invasion, proliferation, colony-formation ability and chemosensitivity of GC cells through the same pathway. Finally, the in vivo test showed similar results, whereby the knockdown of the Bmi-1 gene led to the inhibition of tumor growth, metastasis and chemoresistance through miR-27a and miR-155. Conclusions: Bmi-1 was proven to induce the expression of miR-27a and miR-155 and thus promote tumor metastasis and chemoresistance by targeting RKIP in GC. Overall, miR-27a and miR-155 might be promising targets for the screening, diagnosis, prognosis, treatment and disease monitoring of GC.

Tumor‐associated macrophages (TAMs) are abundant population of inflammatory cells which play an essential role in remodeling tumor microenvironment and tumor progression. Previously, we found the high density of TAMs was correlated with lymph node metastasis and poor prognosis in pancreatic ductal adenocarcinoma (PDAC). Therefore, this study was designed to investigate the mechanisms of interaction between TAMs and PDAC. THP‐1 monocytes were the exposure to conditioned media (CM) produced by PDAC cells; then, monocyte recruitment and macrophage differentiation were assessed. CM from PDAC attracted and polarized THP‐1 monocytes to tumor‐driven like macrophages. mRNA expression cytokine profiling and ELISA identified the IL‐8 secretion was increasing in tumor‐driven like macrophages, and STAT3 pathway was involved. Addition of exogenous recombinant human IL‐8 promoted PDAC cells motility in vitro and metastasis in vivo via upregulating Twist expression, which mediated epithelial‐mesenchymal transition in cancer cells. What is more, IL‐8 expression level in tumor stroma by immunohistochemical analysis was related to lymph node metastasis, the number of tumor CD68 but not CD163 positive macrophages and patient outcome. Taken together, these findings shed light on the important interplay between cancer cells and TAMs in tumor microenvironment and suggested that IL‐8 signaling might be a potential therapeutic target for PDAC.

Objectives: Tumor-associated macrophages (TAMs) are thought to be involved in the perineural invasion (PNI) process and to be associated with poor prognoses. The associations between TAMs, PNI, and clinicopathological features in pancreatic ductal adenocarcinomas (PDAs) remain to be elucidated. Methods: Fifty-nine PDA patients who had undergone pancreaticoduodenectomy were retrospectively examined. The PNI statuses and TAMs were reviewed following H&E staining and S-100, CD68, and CD163 immunohistochemical staining. The relationships between PNI, TAMs, and overall survival and various clinical and histopathologic factors were investigated. Results: PNI was identified in 83% (49/59) of the cases, the TAM density of the PNI⁺ group was greater than that of the PNI^- group, and the infiltrating TAMs around the nerves that were invaded by cancer were much more numerous than those around the nerves without cancer cell invasion. The incidences of PNI, lymph node metastasis, high serum CA19-9 level, cancers in the body/tail, and advanced pathological stage were associated with shorter OSs. In the PNI⁺ group, lymph node metastasis and high levels of TAM infiltration were associated with worse prognoses. Conclusions: TAMs might enhance PNI, and the incidence of PNI was associated with poor prognosis. PNI⁺ status and high levels of TAM infiltration further worsen the prognosis. Therapies targeting TAMs might represent auxiliary and preventive treatment for PNI in PDA patients.