The document compares the inhibitory effects of three transcriptional variants of the CDKN2A gene in the human lung cancer cell line A549. It finds that p16INK4a has the strongest suppressive effect on cell growth compared to p14ARF and p12. Experiments show p16INK4a, p14ARF, and p12 are expressed in A549 cells and lead to cell cycle arrest before DNA replication in the S phase. Protein transduction of the transcriptional variants into A549 cells demonstrates their tumor suppressive effects and potential for protein therapy.