Retinoblastoma protein and gene

3 structural components.
Carboxyl terminal
pocket subunit
Amino terminal
Within each component there are a number of phosphorylation sites.

Phosphorylation causes interdomain locking that changes rb configuration & prevents target binding , inactivating rb.

Different sites are phosphoryated at different times giving rise to a variety of functions

1. Rb & retinoblastoma By D.REIYA BOSCO St. Joseph’s College Trichy

2. They are multifunctional with many binding & phosphorylation sites . Most common function is binding & repressing E2F targets . pRb is protein belongs to pocket protein family . rb proteins have pockets for functional binding of other proteins. Oncogenic proteins bind & inactivate rb proteins eg -HPV . Retinoblastoma protein

3. 3 structural components. Carboxyl terminal pocket subunit Amino terminal Within each component there are a number of phosphorylation sites. Phosphorylation causes interdomain locking that changes rb configuration & prevents target binding , inactivating rb . Different sites are phosphoryated at different times giving rise to a variety of functions.

4. RB gene is responsible for muticellular lineages of life. Located on the long arm of chromosome 13(q). 27 exons & 26 introns . 2 normal copies of rb gene is present in most human cells. Rb gene product is 928 aa phospho protein . Its function is to suppress cell growth . In humans RB 1 gene codes for rb protein. RB gene

5. If both allels of RB gene is inactivated early in life the rb protein is inactivated. This results in retinoblastoma cancer . RB gene is dysfunctional in major cancers. It prevents cell growth by inhibiting cell cycle progression until cell is ready to divide.

6. RB prevents phase transition from G1 – S. RB binds & inhibits E 2 F-DP (promoter-binding-protein- dimerization -partner)-they push cell cycle to S. {Rb-E2F-DP} complex inactivates its function. It attracts histone deacetylase (HDAC). Reduces transcription of S-phase promoting factors & suppressing synthesis. Cell cycle suppression

7. Rb gene has ability to reversibly inhibit DNA repilcation . When rb is activated it leads to down regulation of necessary replication factors. With 72-96h of active rb induction DNA replication factors like MCMs,RPA34,DBF4 showed decreased levels. The process is reversible by induced knockout of rb . Attenuation of proteins by rb gene

8. 3 mechanisms exist through which rb repress transcription of E2F pRb binds to activator domain of activator E2F. pRb recruitment to a promoter, blocks assembly of pre-initiation complex. pRb associate with complex to modify chromatin structure. Mechanism of repressed transcription

9. E2F are a family of proteins whose binding sites are in the promoter region of genes for cell proliferation /progression of cell cycle. E2F 1-5 associate with proteins in pRb family. E2F 6-7 are independent of pRb. E2F is split into 2 - Activators-E2F 1,2,3 Repressors-E2F-4,5,6 pRb binds to activator domain of activator E 2 F s

10. Activator E2F along with E2F4 (repressor) bind exclusively to pRB . pRb binds to activator domain of activator E2F. Blocking E2F activity thereby transcription is repressed. Presence of pRB may change confirmation of TFIIA/D COMPLEX . It generates a less active version with low binding affinity. It even infers with complex formation.

11. pRb recruits some proteins that alter chromatin structure to bind to the E2F regulated promoters . Access to E2F regulated promoters by transcriptional factors is blocked by nucleosome formation & further by chromatin formation. De- acteylation forms nucleosome & makes it difficult for TF to sit on promoters. 2) pRb associate with complex to modify chromatin structure.

12. Rb interacts with HDAC I,HDAC II, HDAC III. With HDAC I –Rb binds to its pocket domain & represses genes at E2F regulated promoters by nucleosome . Cyclin E (G1-S) is repressed at early G1. HDAC- Rb complex is disrupted by cyclin D / CDK4 (they peak at late G1).

13. RB exist in 3 states. Unphosphorylated (G0)-active Monophosphorylated (early G1) Hyperphosphorylated (late G1 after restriction point.)-inactive Activation & inactivation of RB

14. When cell enters G1, cyclinD & CDK 4/6 phoshorylate Rb at a single phosphorylation site. No further phosphorylation occurs. Its experimentally proven that Rb is phosp by the above 2 only. Throughout G1 the exist in 14 isoforms , together called hypophosphorylated Rb. It has a variety of functions & is active upto varying degrees. Monophosphorylation

15. After cell passes the restriction point cyclin E & CDK2 hyperphosphrylates all the monophosphorylated forms. Exact mech is unknown. Hysteric & irreversible. Accumulation of of monophosphates drives this process. H yperphosphorylated

16. retinoblastoma

17. Paevius described retinblastoma in 1597. It was thought to be described from glial cells & was called glioma of retina by virchow (1864). Later it was known that tumor originated from retina & the name retinoblastoma was accepted. Most common intraocular malignancy. H istory

18. Constitutes to 1 of 3 children with rb . Present at birth & is in cells of body including all the cells of both retinas. This is called germline mutations. RB 1 gene mutation is not inherited from parent.(apart from few cases) Genes change during early devp stages in womb . Congenital rb

19. Bilateral retinoblastoma .(both eyes) Multifocal retinoblastoma .(several tumors within the eye) All cells of body have a mutated RB1 gene & cancer could be developed anywhere in the body.

20. 2 of 3 children with rb has this disease. One cell is mutated in one eye. Reason for change is not yet known . Found in children slightly older . Risk of cancer is less when cmpared to congenital. Sporadic rb

21. Cells grow & fill eyeball. metastasis. Tumors block fluid circulation within the eye. Increases the pressure in the eye—leading to Gucoma (pain & loss of vision). Grow along optic nerve 7 reach brain. Gow in eyeball, eyelids , socket,near tissues. S pread

22. Ophthalmoscope. Biopsy confirms it. White colour in the center of eye. Squint. Redness & swelling. Diagnosis S ymptoms

23. Thank you