Retinoblastoma protein

A tumor suppressor protein involved in cell cycle regulation

The retinoblastoma protein (Rb) is a crucial tumor suppressor protein that plays a pivotal role in regulating the cell cycle. It is encoded by the RB1 gene located on chromosome 13q14.1-q14.2. The protein is named after retinoblastoma, a rare type of eye cancer that primarily affects young children, as mutations in the RB1 gene were first identified in this disease.

Function

The primary function of the retinoblastoma protein is to control the progression of cells through the G1 phase of the cell cycle. Rb exerts its effects by binding to and inhibiting the activity of the E2F family of transcription factors, which are essential for the transition from the G1 phase to the S phase of the cell cycle. By inhibiting E2F, Rb prevents the transcription of genes required for DNA replication, thereby halting cell cycle progression.

Rb is regulated by phosphorylation. In its hypophosphorylated state, Rb is active and can bind to E2F, inhibiting its activity. As the cell progresses through the G1 phase, Rb becomes phosphorylated by cyclin-dependent kinases (CDKs), such as CDK4/6 in complex with cyclin D. This phosphorylation inactivates Rb, releasing E2F and allowing the transcription of genes necessary for S phase entry.

Passing the restriction point triggers immediate hyper-phosphorylation of mono-phosphorylated Rb

Role in Cancer

Mutations in the RB1 gene can lead to the loss of Rb function, resulting in uncontrolled cell proliferation and tumor development. Such mutations are commonly associated with retinoblastoma, but they are also found in a variety of other cancers, including osteosarcoma, breast cancer, and small cell lung cancer.

The loss of Rb function disrupts the normal regulation of the cell cycle, allowing cells to bypass the G1 checkpoint and proliferate uncontrollably. This makes Rb a critical target for cancer research and therapy.

Interactions

Rb interacts with several other proteins and pathways involved in cell cycle regulation and tumor suppression. These include:

• p53, another tumor suppressor protein that regulates the cell cycle and apoptosis.
• Cyclin-dependent kinase inhibitors such as p16, which prevent the phosphorylation of Rb.
• Histone deacetylases (HDACs), which are recruited by Rb to repress transcription.

Also see

• Cell cycle
• Tumor suppressor gene
• E2F transcription factor
• Cyclin-dependent kinase
• Retinoblastoma

External links

• RB1 gene - NCBI
• Retinoblastoma and RB1 - National Cancer Institute