Expression of cyclin A1 in different cell lines. Expression of human cyclin A1 mRNA in human tumor cell lines was analyzed by Northern blotting of 10 μg of total RNA and hybridization with a ³²P-labeled cyclin A1-specific probe. The levels of 28S RNA show that equal amounts of RNA were loaded. HeLa (cervical carcinoma) and PC3 (prostate cancer) cell lines were derived from solid tumors, and U937 and Kcl22 were established from leukemic blasts.