Introduction:
Uveal melanoma is known as a frequent intraocular tumor, with high metastasis and poor prognosis. Mitogen- and stress-activated protein kinase 1 (MSK1) is a serine/threonine kinase that has been reported to be associated with tumor progression in several types of human cancer. However, the role of MSK1 has rarely been studied in uveal melanoma and the underlying mechanism remained unclear.

Material and methods:
The expression level of MSK1 in human uveal melanoma tissues and normal uveal tissues was determined by qRT-PCR analysis, western blotting and immunohistochemistry (IHC). Subsequently, MTT assay, colony formation assay and flow cytometry assay were performed to assess the effects of MSK1 on cell proliferation. Wound-healing and transwell chamber assays were adopted to clarify the role of MSK1 in cell metastasis. Finally, the function of MSK1 was confirmed in vivo in a tumor-bearing mouse model.

Results:
The expression levels of MSK1 and p-cyclic AMP-responsive element binding protein (CREB) were strongly up-regulated in human uveal melanoma tissues. MSK1 overexpression facilitated cell viability and clone formation, and promoted migration and invasion of uveal melanoma cells. However, mutation of cyclic AMP-responsive element binding protein (CREB) at Ser133 residues reversed the effect of MSK1 on uveal melanoma cell proliferation and metastasis. The in vivo experiment suggested that the tumor weight was lower and the tumor mass grew more slowly in the shMSK1 group as compared to the shNC group.

Conclusions:
MSK1 promotes proliferation and metastasis of uveal melanoma cells by phosphorylated CREB at Ser133 residues. Therefore, MSK1 could be a promising candidate for uveal melanoma therapy and especially has tremendous potential in the treatment of cancers in which the MSK1-CREB pathway is abnormally active.