An optical labeling-based proliferation assay system reveals the paracrine effect of interleukin-6 in breast cancer

Junji Itou, Sunao Tanaka, Fumiaki Sato, Ryutaro Akiyama, Yasuhiko Kawakami, Masakazu Toi

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


Proliferation analysis is one of the basic approaches to characterize various cell types. In conventional cell proliferation assays, the same sample cannot be observed over time, nor can a specific group within a heterogeneous population of cells, for example, cancerous cells, be analyzed separately. To overcome these limitations, we established an optical labeling-based proliferation assay system with the Kaede protein, whose fluorescence can be irreversibly photoconverted from green to red by irradiation. After a single non-toxic photoconversion event, the intensity of red fluorescence in each cell is reduced by cell division. From this, we developed a simple method to quantify cell proliferation by monitoring reduction of red fluorescence over time. This study shows that the optical labeling-based proliferation assay is a viable novel method to analyze cell proliferation, and could enhance our understanding of mechanisms regulating cell proliferation machinery. We used this newly established system to analyze the functions of secreted interleukin-6 (IL-6) in cancer cell proliferation, which had not been fully characterized. Reduction in proliferation was observed following IL-6 knockdown. However, after co-culturing with IL-6-expressing cells, the proliferation of Kaede-labeled IL-6-knockdown cells was restored. These data indicate that in basal-like breast cancer cells, IL-6 exhibits a paracrine effect to positively regulate cell proliferation. Our results thus demonstrate that cancer cells can secrete signaling molecules, such as IL-6, to support the proliferation of other cancer cells.

Original languageEnglish (US)
Pages (from-to)27-40
Number of pages14
JournalBiochimica et Biophysica Acta - Molecular Cell Research
Issue number1
StatePublished - Jan 1 2015

Bibliographical note

Funding Information:
We thank Dr Kunio Kitada, Dr Yasuko Miyake, Dr Elham Fakhrejahani, Dr Fengling Pu and Ms Kayoko Koishihara for technical assistance. We thank Dr Isao Oishi and Dr Yoshiaki Matsumoto for editorial assistance. We thank the members of the Departments of Breast Surgery, and of Hepato-biliary-pancreatic Surgery and Transplantation for sharing laboratory equipment. Confocal imaging and time-lapse analysis using Leica TCS SP8 were performed at the Medical Research Support Center, Graduate School of Medicine, Kyoto University. This study was supported by JSPS Grant-in-Aid for Young Scientists (B) No. 25870384 . Financial support was provided by Taiho Pharmaceutical Cd. Ltd .

Publisher Copyright:
© 2014 Elsevier B.V.


  • Breast cancer
  • Interleukin-6
  • Optical labeling
  • Paracrine effect
  • Proliferation
  • The OPA system


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