INK4 is a tumour suppressor protein. It is associated with several genes, including p16INK4a and p14ARF, and with several other proteins, like HRAS. [1] Lack of this protein has been associated with several types of cancer, including bladder and melanoma. The 'INK4' label is given to three proteins: INK4A and INK4B. These proteins act to inhibit cdk4 and cdk6 upon binding, causing the arrest of the cell cycle in G1. [2]