IL-9 inhibits HTB-72 melanoma cell growth through upregulation of p21 and TRAIL.

Background: IL-9 is a pleiotropic cytokine produced mainly by Th9 cells. IL-9 may have an anti-proliferative role in murine melanoma, however, its effect on human melanoma is unknown.

Methods: We examined the effects of IL-9 on proliferation and apoptosis in four human melanoma cell lines, HTB-65, HTB-72, CRL-11147, and SK-Mel-5. Clonogenic assay, PCNA staining, Quick Cell Proliferation assay, TUNEL staining and caspase-3 activity assay were used to assess proliferation and apoptosis, as appropriate.

Results: We found that IL-9 decreased the percentage of colonies of HTB-72 and SK-Mel-5 cells but not that of HTB-65 or CRL-11147 cells. PCNA mRNA, PCNA+ cells, PCNA staining intensity, and the OD value of HTB-72 melanoma cells were consistently decreased in the present of IL-9. IL-9 also increased TUNEL+ cells and the relative caspase-3 activity in HTB-72 melanoma cells. We further investigated the possible molecular mechanisms using RT-PCR and immunohistochemical staining. The anti-proliferative effect of IL-9 on HTB-72 cells correlated with higher expression of anti-proliferative molecule p21. Its pro-apoptotic effect on HTB-72 cells correlated with higher expression of the pro-apoptotic molecule TRAIL.

Conclusions: IL-9 inhibits melanoma HTB-72 cell growth by upregulation of p21 and TRAIL. Understanding the interactions between IL-9 and melanoma may help direct strategies for cytokine-based immunotherapy development.