No abstract

Tumor-associated macrophages (TAMs), the main part of immune cells in tumor microenvironment (TME), play a potent role in promoting tumorigenesis through mechanisms such as stimulating angiogenesis, enhancing tumor migration and suppressing antitumor immunity. MicroRNAs (miRNAs) are considered as crucial regulators in multiple biological processes. The relationship between miRNAs and macrophages function has been extensively reported, but the roles that miRNAs play in regulating TAMs phenotype remain unclear. In this study, we screened highly expressed microRNAs in TAMs, and first identified that miR-100 represented a TAMs-high expression pattern and maintained TAMs phenotype by targeting mTOR signaling pathway. Moreover, miR-100 expression level in TAMs was positively related to IL-1ra secretion, a traditional immune-suppressive cytokine, which was determined to promote tumor cells stemness via stimulating Hedgehog pathway. Mechanism study suggested that mTOR/Stat5a pathway was involved in IL-1ra transcriptional regulation process mediated by miR-100. More importantly, tumor metastasis and invasion capacity were significantly decreased in a 4T1 mouse breast cancer model injected intratumorally with miR-100 antagomir, and combination therapy with cisplatin showed much better benefit. In this study, we confirm that highly expressed miR-100 maintains the phenotype of TAMs and promotes tumor metastasis via enhancing IL-1ra secretion. Interfering miR-100 expression of TAMs in mouse breast cancer model could inhibit TAMs pro-tumor function and reduce tumor metastasis, which suggests that miR-100 could serve as a potential therapy target to remodel tumor microenvironment in breast cancer.

Considerable evidence suggests that proinflammatory pathways drive self-renewal of cancer stem-like cells (CSC), but the underlying mechanisms remain mainly undefined. Here we report that the let7 repressor LIN28B and its regulator IKBKB (IKKb) sustain cancer cell stemness by interacting with the Wnt/TCF7L2 (TCF4) signaling pathway to promote cancer progression. We found that LIN28B expression correlated with clinical progression and stemness marker expression in breast cancer patients. Functional studies demonstrated that the stemness properties of LIN28B-expressing human breast and lung cancer cells were enhanced by IKKb, whereas loss of LIN28B abolished stemness properties in these settings. These phenomena were driven through interactions with TCF7L2, which enhanced LIN28B expression by direct binding to intron 1 of the LIN28B gene, which in turn promoted TCF7L2 mRNA translation through a positive feedback loop. Notably, RNAimediated silencing of LIN28B or pharmacologic inhibition of IKKb was sufficient to suppress primary and metastatic tumor growth in vivo. Together, our results establish the LIN28B/ TCF7L2 interaction loop as a central mediator of cancer stemness driven by proinflammatory processes during progression and metastasis, possibly offering a new therapeutic target for generalized interventions in advanced cancers.

This study was conducted to determine the role of neuregulin 1 (NRG1)-dependent human epidermal growth factor receptor 3 (HER3) activation in trastuzumab primary resistance, and to observe the inhibitory effect of HER3 monoclonal antibody on HER2-overexpressing breast cancer cells. BT474 cells (trastuzumab sensitive) and MDA-MB-453 cells (trastuzumab resistant) were first stimulated with NRG1 and then treated with either trastuzumab, HER3 antibody, or a combination of both. The expression of phospho human epidermal growth factor receptor 2 (p-HER2), phospho human epidermal growth factor receptor 3 (p-HER3), phospho protein kinase B (p-Akt) and phospho mitogen-activated protein kinase (p-MAPK) were detected by western blotting. Apoptosis was detected by flow cytometry. Cell viability was detected by MTT assay. Without NRG1 stimulation, trastuzumab treatment significantly down-regulated the expression of p-HER2, increased early apoptosis, and decreased cell viability in BT474 cells. After NRG1 stimulation, the aforementioned effects weakened or disappeared in the trastuzumab treatment group, whereas in the HER3 antibody treatment group, there was significant downregulation in p-HER3 expression and increase in early apoptosis of BT474 cells. In MDA-MB-453 cells, the HER3 antibody significantly downregulated both p-HER2 and p-HER3 and promoted early apoptosis after NRG1 stimulation, however, trastuzumab hardly played a role. p-Akt and p-MAPK were also significantly downregulated by the HER3 antibody after NRG1 stimulation. The expressions of p-HER2, p-HER3, p-Akt and p-MAPK were all downregulated after HER3 gene silencing, compared to the control. NRG1-dependent activation of HER3 induces primary resistance to trastuzumab in HER2-overexpressing breast cancer cells. HER3 monoclonal antibody combined with trastuzumab may serve as a treatment choice for patients with primary resistance to trastuzumab.