RB1

The retinoblastoma protein (protein name abbreviated pRb; gene name abbreviated RB or RB1) is a tumor suppressor protein that is dysfunctional in several major cancers.

One function of pRb is to prevent excessive cell growth by inhibiting cell cycle progression until a cell is ready to divide. When the cell is ready to divide, pRb is phosphorylated, becomes inactive and allows cell cycle progression. It is also a recruiter of several chromatin remodeling enzymes such as methylases and acetylases.

Rb belongs to the pocket protein family, whose members have a pocket for the functional binding of other proteins. Should an oncogenic protein, such as those produced by cells infected by high-risk types of human papillomaviruses, bind and inactivate pRb, this can lead to cancer.

Functions

 Cell cycle regulation

In a resting cell, RB is a component of the E2F/DP1/RB complex, which represses gene transcription through the recruitment of histone deacetylase, an enzyme that alters the conformation of chromatin, making it more compact.

Phosphorylation of RB by cyclin D-CDK4 removes histone deacetylase from chromatin, allowing the activation of E2F transcriptional activity (RB can also be phosphorylated by cyclin E-CDK2).

E2F-mediated transcription of cyclins E and A, and of genes required for DNA replication, permit the passage through the G1 restriction point.

Tumor predisposition

 RB1-associated tumor predisposition syndrome

• retinoblastoma
• post-radiation osteosarcoma

Pathology

 germline mutations in familial retinoblastoma
 somatic mutations in:

• sporadic retinoblastoma
• post-radiation osteosarcoma

 inactivation of RB protein by HPV-E6 and HPV-E7 oncoproteins through p16 protein (CDKN2A)

• p16 is an inhibitor of cyclin dependent kinases such as CDK4 and CDK6.
• These latter kinases phosphorylate retinoblastoma protein (pRB) which eventually results in progression from G1 phase to S phase.

Immunochemistry

 Loss of retinoblastoma protein expression in spindle cell/pleomorphic lipomas and cytogenetically related tumors: an immunohistochemical study with diagnostic implications. (22790852)

Features

 RB/E2F pathway (P16(INK4A)-CDK4/6-RB)

References

 Loss of retinoblastoma protein expression in spindle cell/pleomorphic lipomas and cytogenetically related tumors: an immunohistochemical study with diagnostic implications. Chen BJ, Mariño-Enríquez A, Fletcher CD, Hornick JL. Am J Surg Pathol. 2012 Aug;36(8):1119-28. PMID: 22790852

 Deshpande A, Hinds PW. The retinoblastoma protein in osteoblast differentiation and osteosarcoma. Curr Mol Med. 2006 Nov;6(7):809-17. PMID: 17100605

 Jones EE, Wells SI. Cervical cancer and human papillomaviruses: inactivation of retinoblastoma and other tumor suppressor pathways. Curr Mol Med. 2006 Nov;6(7):795-808. PMID: 17100604

 Wikenheiser-Brokamp KA. Retinoblastoma regulatory pathway in lung cancer. Curr Mol Med. 2006 Nov;6(7):783-93. PMID: 17100603

 Pacal M, Bremner R. Insights from animal models on the origins and progression of retinoblastoma. Curr Mol Med. 2006 Nov;6(7):759-81. PMID: 17100602

 Knudsen ES, Sexton CR, Mayhew CN. Role of the retinoblastoma tumor suppressor in the maintenance of genome integrity. Curr Mol Med. 2006 Nov;6(7):749-57. PMID: 17100601

 Dasgupta P, Padmanabhan J, Chellappan S. Rb function in the apoptosis and senescence of non-neuronal and neuronal cells: role in oncogenesis. Curr Mol Med. 2006 Nov;6(7):719-29. PMID: 17100598

 Delston RB, Harbour JW. Rb at the interface between cell cycle and apoptotic decisions. Curr Mol Med. 2006 Nov;6(7):713-8. PMID: 17100597

 Korenjak M, Brehm A. The retinoblastoma tumour suppressor in model organisms—new insights from flies and worms. Curr Mol Med. 2006 Nov;6(7):705-11. PMID: 17100596

 Liu H, Dibling B, Spike B, Dirlam A, Macleod K. New roles for the RB tumor suppressor protein. Curr Opin Genet Dev. 2004 Feb;14(1):55-64. PMID: 15108806

 Chau BN, Wang JY. Coordinated regulation of life and death by RB. Nat Rev Cancer. 2003 Feb;3(2):130-8. PMID: 12563312

 Classon M, Harlow E. The retinoblastoma tumour suppressor in development and cancer. Nat Rev Cancer. 2002 Dec;2(12):910-7. PMID: 12459729

 Nevins JR. The Rb/E2F pathway and cancer. Hum Mol Genet. 2001 Apr;10(7):699-703. PMID: 11257102

 Korenjak M, Brehm A. E2F-Rb complexes regulating transcription of genes important for differentiation and development. Curr Opin Genet Dev. 2005 Oct;15(5):520-7. PMID: 16081278

 Blais A, Dynlacht BD. Hitting their targets: an emerging picture of E2F and cell cycle control. Curr Opin Genet Dev. 2004 Oct;14(5):527-32. PMID: 15380244

 Nevins JR. The Rb/E2F pathway and cancer. Hum Mol Genet. 2001 Apr;10(7):699-703. PMID: 11257102