This gene produces several transcript variants with different first exons. At least three spliced variants encode distinct proteins, two of which are CDK4 kinase inhibitors. The third variant includes an alternate first exon and open reading frame (ARF), encoding a protein that stabilizes the tumor suppressor p53. This ARF product interacts with and sequesters MDM2, an E3 ubiquitin ligase that degrades p53. Despite structural differences, both the CDK inhibitor isoforms and ARF product share a common role in regulating G1 progression of the cell cycle through CDK4 and p53. This gene is frequently mutated or deleted in many tumors, making it an important tumor suppressor.