Tumor-suppressor microRNA-139-5p restrains bladder cancer cell line ECV-304 properties via targeting Connexin 43

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Tumor-suppressor microRNA-139-5p restrains bladder cancer cell line ECV-304 properties via targeting Connexin 43

Bladder cancer is the 10th most common cancer worldwide, with over 549,000 new cases reported in 2018. Despite advances in diagnosis and treatment, its 5-year survival rate has barely improved—and researchers are racing to uncover new ways to stop it. A 2019 study from Chinese Medical Journal offers a promising clue: a small molecule called microRNA-139-5p (miR-139-5p) may act as a “brake” on bladder cancer growth by targeting a protein named Connexin 43 (CX43). Here’s what you need to know.

The Players: MiR-139-5p and CX43

First, let’s break down the science. MicroRNAs (miRNAs) are tiny, non-coding RNAs that regulate how genes are expressed. Think of them as “dimmer switches” for your DNA—they don’t change the gene itself, but they can turn its activity up or down. Connexin 43 (CX43) is a protein that helps cells communicate with each other through “gap junctions”—channels that let small molecules pass between neighboring cells. In previous work, the study’s authors found CX43 is overexpressed in bladder cancer tissues, meaning it’s more active than normal and may promote tumor growth.

The big question: Could a miRNA like miR-139-5p “turn down” CX43—and in turn, slow bladder cancer?

What the Study Did

Led by Qiang Chi and colleagues from the Department of Urology at the Affiliated Hospital of Chengde Medical University (China), the research combined two key approaches:

  1. Data Analysis: They used The Cancer Genome Atlas (TCGA)—a public database of cancer genetics—to compare miR-139-5p levels in 418 bladder cancer tissues and 19 healthy “paracancer” tissues.
  2. Cell Experiments: They worked with three human bladder cancer cell lines (5637, T24, ECV-304) and a healthy bladder cell line (SV-HUC-1). They:
    • “Transfected” cells with miR-139-5p “mimics” (to boost miR-139-5p levels) or “si-CX43” (to knock down CX43).
    • Used techniques like qRT-PCR (to measure gene activity) and Western blotting (to measure protein levels) to track miR-139-5p and CX43.
    • Tested cell proliferation (with a CCK-8 assay), migration, and invasion (with transwell chambers).
    • Used a dual-luciferase reporter assay to confirm if miR-139-5p directly binds to CX43’s genetic code (the 3’UTR region).

Key Findings

The results were clear—and promising:

1. MiR-139-5p is low in bladder cancer

TCGA data showed miR-139-5p levels were 30% lower in bladder cancer tissues than in healthy ones (2.29 vs. 3.21, P < 0.0001). The same pattern held in cancer cell lines: miR-139-5p was significantly lower in 5637, T24, and ECV-304 cells compared to healthy SV-HUC-1 cells (P < 0.01 for all).

2. Boosting miR-139-5p slows cancer cells

When the team increased miR-139-5p levels in ECV-304 and T24 cells (using mimics), they found:

  • Reduced proliferation: Cell growth dropped by ~30% in ECV-304 (P = 0.001) and ~25% in T24 (P = 0.005) compared to control cells.
  • Less migration and invasion: The number of cells that moved through transwell chambers (a sign of metastasis) fell by ~50% in ECV-304 cells (P = 0.001 for both migration and invasion).

3. MiR-139-5p directly targets CX43

The dual-luciferase assay confirmed the “smoking gun”: miR-139-5p binds to the 3’UTR of CX43’s mRNA. When cells were given miR-139-5p mimics, the activity of a “wild-type” CX43 gene (with the intact binding site) dropped by ~60% (P = 0.002). A “mutant” CX43 gene (with a broken binding site) was unaffected—proof that miR-139-5p specifically targets CX43.

4. Knocking down CX43 makes miR-139-5p even more effective

To test if CX43 is the key mediator of miR-139-5p’s effects, the team knocked down CX43 in ECV-304 cells while boosting miR-139-5p. The result? Cell proliferation, invasion, and migration dropped even further than when miR-139-5p was boosted alone (P < 0.01 for proliferation; P = 0.028 for invasion; P = 0.014 for migration).

Why This Matters

Bladder cancer is tough to treat because it often recurs and spreads. These findings add two important pieces to the puzzle:

  • MiR-139-5p is a tumor suppressor: Its low levels in bladder cancer mean it’s not doing its job—stopping tumor growth. Boosting it could be a new treatment strategy.
  • CX43 is a critical target: Since miR-139-5p works by turning down CX43, targeting CX43 directly (or via miR-139-5p) could slow cancer progression.

The study also aligns with broader research: miR-139-5p acts as a tumor suppressor in other cancers (like lung, endometrial, and colorectal), and CX43 overexpression is linked to poor survival in bladder cancer patients.

The Takeaway

This research doesn’t just add to scientific knowledge—it points to potential new treatments. If miR-139-5p or CX43 can be targeted in patients (e.g., with miRNA mimics or CX43 inhibitors), it could offer a way to slow bladder cancer growth and metastasis.

Of course, more work is needed: animal studies and clinical trials will be key to confirming these effects in living organisms. But for a disease where progress has been slow, this study is a step forward.

Qiang Chi, Zhi-Yong Wang, Hong-Yang Li, Dian-Bin Song, Hui Xu, Guang Ma, Ze-Min Wang, Xiu-Ming Li
Department of Urology, Affiliated Hospital of Chengde Medical University, Chengde, Hebei 067000, China

Originally published in Chinese Medical Journal 2019;132(19):2354–2361.

doi:10.1097/CM9.0000000000000455

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