MicroRNAs 15A and 16-1 Activate Signaling Pathways That Mediate Chemotaxis of Immune Regulatory B cells to Colorectal Tumors

5 years ago

MicroRNAs 15A and 16-1 Activate Signaling Pathways That Mediate Chemotaxis of Immune Regulatory B cells to Colorectal Tumors

B cells infiltrate tumors but little is known about how they affect tumor growth and progression. microRNA15A (MIR15A or miRNA15A) and microRNA16-1 (MIR16-1 or miRNA16-1) regulate cell proliferation, apoptosis and drug resistance. We investigated their involvement in B cell–mediated immune suppression by colorectal tumors.

Methods

Mice with disruptions of the gene cluster that encodes MIR15A and MIR16-1 (KO mice), and control (C57BL/B6) mice were given azoxymethane with dextran sodium sulfate (AD) to induce formation of colorectal tumors. Mice were given anti-CD20 to delete B cells, or injections of agomir to increase MIR15A and MIR16-1. Proliferation of CD8⁺T cells was measured by carboxyfluorescein-succinimidyl-ester analysis. Colon tissues were collected form mice and analyzed by flow cytometry, microRNA sequencing, and for cytokine production. Intestinal epithelial cells (IECs) were isolated and transfected with microRNA mimics, to identify their targets. We analyzed miRNA expression patterns and quantified B cells in colorectal cancer tissue microarrays derived from 90 patients who underwent surgical resection, from July 2006 through April 2008, in Shanghai, China; expression data was compared with clinical outcomes.

Results

Tumors that developed in KO mice following administration of AD were larger and contained greater numbers of B cells than tumors than grew in control mice. Most of the B cells in the tumors were positive for immunoglobulin A (IgA⁺). IgA⁺B cells expressed high levels of immune-regulatory molecules (PD-L1, interleukin 10 [IL10], and TGFB), and repressed the proliferation and activation of CD8⁺T cells. Levels of MIR15A and MIR16-1 were reduced in colon tumors from mice, compared with non-tumor colon tissue. Incubation of IECs with IL17A reduced expression of MIR15A and MIR16-1. Transgenic expression of MIR15A and MIR16-1 in IECs decreased activation of NF-κB and STAT1 by reducing expression of I-kappaB kinases; this resulted in reduced production of CXCL9 and CXCL10 and decreased chemotaxis of IgA⁺B cells. Tumors in mice injected with AD and agomir grew more slowly than tumors in mice not given in agomir and contained fewer IgA⁺B cells. We found a negative correlation between levels of MIR15A and MIR16-1 and numbers of IgA⁺B cells in human colorectal tumor tissues; high levels of MIR15A and MIR16-1 and low numbers of IgA⁺B cells associated with longer survival times of patients.

Conclusions

We found increased levels of MIR15A and MIR16-1 to reduce numbers of IgA⁺B cells in colorectal tumor tissues and correlate with increased survival time of patients. In mice that lack MIR15A and MIR16-1, colon tumors grow more rapidly and contain increased numbers of IgA⁺B cells. MIR15A and MIR16-1 appear to activate signaling pathways required for B cell–mediated immune suppression.

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DOI: S0016508517362406