STK11 and lung carcinoma: We infected human LKB1-null lung cancer A549 cells with the CRTC1-CBD-nls-GFP or GFP (control) retroviruses and observed that CRTC1-CBD-nls-GFP was predominantly localized in the nuclear compartment, while the control GFP showed diffuse cytoplasmic and nuclear signals (Figure 3B).