Gene Expression and Retinoblastoma “Cancer of the Eye” School of Medicine, Health Sciences and Engineering Susquehanna Township High School Lecture Series  Week 9, September 2013 Clinical Relevance of This Week’s Topic Gene Expression and Retinoblastoma “Cancer of the Eye” Wen Jie Zhang, MD, PhD

Eyes that look at the world

Eyes that guard our homes

Eyes that work at night

Eyes that look at us on Halloween

Eyes that can talk

Eyes that look at the future

Eyes that may lose vision Retinoblastoma, Rb

Anatomy of the Eye

Retinoblastoma (Rb) Cancer of the Eye Rapid developing cancer of the childhood Outgrowth of immature cells of the Retina, the light-detecting tissue in the eye Diagnosed: 90% of Rb within the first 3 years of age the remaining within the 6 years of age Very rare after 6 years of age Incidence of 18,000 to 30,000 live births worldwide

Retinoblastoma (Rb) Categories (Types) Familial Rb Hereditary and bilateral (affects both eyes) Approx 10% Sporadic Rb Non-hereditary and unilateral (affects one eye) Approx 70%

Retinoblastoma (Rb) Signs Leukocoria (white pupil, 60% of Rb)

Retinoblastoma (Rb) Signs Strabismus (squint, cross-eye, 20% of Rb)

Retinoblastoma (Rb) Signs Other signs (10% of Rb) Eye swelling with pain and redness

Funduscopic finding of a retinoblastoma

Funduscopic finding of a retinoblastoma

Migration of retinoblastoma “seeds“ onto the iris surface.

A Drawing of Retinoblastoma J. Wardrop, 1809

A Surgically Removed Retinoblastoma

Mechanism(s) of Retinoblastoma

Carcinogenesis Environmental Factors Genetic Factors (Carcinogens) Physical Chemical Biological (Mutations) Substitutions Deletions Insertions Lifestyle Cancer (Carcinogens) Translocations

Tumor Suppressor Genes Gene Human Disease Function APC Colon cancer Interacts with catenins DCC Colon cancer CAM domains E-cadherin Breast cancer Intracellularly interacts (CDH1) with catenins DPC4 Pancreatic cancer TGF--related signaling BRCA1 Mammary cancer/ DNA damage repair, Ovarian cancer checkpoint control, apoptosis BRCA2 Mammary cancer DNA damage repair, genomic stability ATM Ataxia-telangiectasia DNA damage response mutated gene upstream in p53 pathway P53 Mutated in >50% Transcription factor, tumors checkpoint control, apoptosis

Mechanism(s) of Retinoblastoma RB1 gene encodes a protein (pRb) that serves as a tumor suppressor Suppress cell (division) cycle Mutation of RB1 gene Results a defective pRb protein, therefore, unable to suppress cell cycle leading uncontrolled cell division (tumor formation)

Cell Division Cycle Under Control

If not controlled, Cancer (tumor) Formation

RB1 Gene Location RB1 gene 13q14.1-q14.2

of Retinoblastoma Protein (pRb) Crystal Structure of Retinoblastoma Protein (pRb)

Crystal Structure of the Retinoblastoma Tumor Suppressor Protein Bound to E2F Retinoblastoma Protein is colored blue, E2F is violet

Carcinogenesis – “Two-hit” Hypothesis (Knudson, 1971) First hit Second hit Outcome Multi-step process Germline Mutation (Insertion/ Deletion) First Mutation (Insertion/Deletion) Inherited Before birth Second Mutation (Insertion/Deletion) Acquired After birth Cancer develops Genetic Somatic

“Two-hit” Hypothesis Familial Rb fits the hypothesis First hit: One mutated gene inherited (recessive) Second hit: Another gene is also mutated due to different reason(s) (e.g., UV radiation, reported in New Zealand)

Common Mutations Substitutions (point mutation) In a DNA sequence, a single nucleotide is exchanged for another (A G, C T), leading to missense or nonsense mutation. Insertions (insertion mutation) The addition of one or more nucleotide base pairs into a DNA sequence. Deletions (deletion mutation) Part of a chromosome or a sequence (base pairs) of DNA is missing from a DNA sequence.

Genetic Testing “Well Baby Screening” for Signs for Early Diagnosis Several methods for detecting the RB1 gene mutations have been developed A method that can detect large deletions in the RB1 gene that correlate with advanced stage retinoblastoma “Well Baby Screening” for Signs for Early Diagnosis

Treatment Simple enucleation (removal of the eye) Eye-sparing radiotherapy Chemotherapy-based multi-modality therapy Laser therapy Cryotherapy (freezing therapy at −196ºC or −321ºF) 

Images of Retinoblastoma (Rb) tumors by Retino-scan before and during chemotherapy

Outcomes Rb has one of the best cure rates (95-98%) among all childhood cancers 9 out of every 10 patients survive into adulthood

Eyes that look at the future

The Coda