INK4

INK4 is a family of proteins that function as tumor suppressors. These proteins are known to regulate the cell cycle, specifically the progression from the G1 phase to the S phase. The INK4 family includes four members: p16INK4a, p15INK4b, p18INK4c, and p19INK4d.

Function

The INK4 family proteins bind to cyclin-dependent kinases (CDK4 and CDK6) and inhibit their activity, thereby preventing the phosphorylation of the retinoblastoma protein (Rb). This results in the arrest of the cell cycle in the G1 phase. The INK4 proteins are thus critical in preventing uncontrolled cell proliferation, which is a hallmark of cancer.

Structure

INK4 proteins have a common structural motif known as the ankyrin repeat, which is involved in protein-protein interactions. Each INK4 protein has four ankyrin repeats, which are responsible for the binding to CDK4/6.

Role in Cancer

Mutations in the genes encoding INK4 proteins are frequently observed in various types of cancer. For example, the gene encoding p16INK4a is one of the most commonly mutated genes in human cancer. Inactivation of this gene leads to uncontrolled cell proliferation and tumor development.

See Also

• Cyclin-dependent kinase
• Retinoblastoma protein
• Cell cycle
• Cancer

References

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