Immunoblot analysis of GFP-PN2-3 in HeLa Tet-Off inducible cell lines. The cellular proteins prepared from four established GFP-PN2-3-inducible cell lines after withdrawal of doxycycline at the indicated time points (D: days) were subjected to immunoblotting using anti-GFP antibody. The lower band may represent a degradation product of GFP-PN2-3.