Effect of cisplatin treatment on speckled distribution of a serine/arginine-rich nuclear protein CROP/Luc7A.

The C-half of cisplatin resistance-associated overexpressed protein (CROP), an SR-related protein, comprises domains rich in arginine and glutamate residues (RE domain), and is rich in arginine and serine residues (RS domain). We analyzed the role of the individual domains of CROP in cellular localization, subnuclear localization, and protein-protein interaction. CROP fused with green fluorescent protein, GFP-CROP, localized exclusively to the nucleus and showed a speckled intranuclear distribution. The yeast two-hybrid system revealed that CROP interacted with SF2/ASF, an SR protein involved in RNA splicing, as well as CROP itself. The RE and RS domains were necessary for both the intranuclear speckled distribution and the protein-protein interaction. CROP was phosphorylated by mSRPK1, mSRPK2, and Clk1 in vitro, and when cells were treated with cisplatin the subnuclear distribution of GFP-CROP was changed. These results suggest that cisplatin affects RNA splicing by changing the subnuclear distribution of SR proteins including CROP.