Molecular Pathogenesis of Disease (Hem-Mal I)

Question 1

What are the two general ways in which translocations create malignancies?
• Which category does the Philadelphia chromosome fall in?
•what chromosomes are involved?
• Gene product?
• What disease(s) is/are caused?

Answer 1

Two Categories:

1. Gene gets translocated next to an extremely active promoter
2. Abnormal Fusion proteins are generated

Philadelphia Chromosome
• BCR-ABL fusion protein is the result of a t(9,22)

Disease:
** CHRONIC MYELOGENOUS LEUKEMIA (CML)
AND
**ACUTE LYMPHOBLASTIC LEUKEMIA (ALL)

Question 2

PHILADELPHIA CHROMOSOME
• Translocation? 
• Domains that aid Migration of gene Product?  
• Drug Target 
• Pathway(s) Activated?

Answer 2

t(9,22) - BCR-ABL => CML or ALL

Migration:
• RHO - multipurpose signal transduction domain
• DNA Binding Domain
• Actin Binding Domain

Drug Target:
• AUTOPHOSPHORYLATING Tyrosine Kinase Domain

Pathways Activated: 
• STAT activation => Proliferation and Differentiation**
• PI3 Kinase Activation
• Ras/MEK pathway
• SRC kinase Activation

Question 3

What translocation results in PML?
• Important genes on each chromosome?
• Job of Gene Products?
• Inhibition of Gene Products?

Answer 3

PML = Promyelocytic Leukemia = t(15,17)

Chromosome 15
• PML gene: Facilitates Nuclear Localization of Binding Partners
• Inhibition = built in degradation mechanism at K160

Chromosome 17
• RARa gene: Transcription Factor that IMPAIRS Granulocyte Differentiation (not proliferation)
• Retanoic acid binds and induces degradation

Question 4

How does the K160 degradation mechanism of the PML gene work?

Answer 4

*Induced by Arsenic Trioxide and ubiquitinates the protein acting as a kill switch

Question 5

What type of cancer gene is p53?
• what prognosis comes from a cancer that lacks p53?
• explain reason for this prognosis.

Answer 5

**Tumor Suppressor gene
• Two Hit Hypothesis applies here

Prognosis of No p53:
• Very poor prognosis, this is because p53 is important in inducing apoptosis in the case of irreparable gene damage.
• Most Cancer drugs work by damaging genes to the extent that the cell undergoes apoptosis. Without an apoptotic regulator the cell can live on.

**Very limited therapy options

Question 6

T or F: cancers resulting from PML-RARA mutations tend to be very treatable.

Answer 6

True

Question 7

What is the normal function of CBF (core binding factor)?

• What types of cancer result from suppression of this function?

Answer 7

NORMAL FUNCTION

CBF (chromosome 16)
• Binds to make heterodimer with Runx1 (chrom. 21)

CBF-Runx1 dimer has 2 functions:

1. bind to DNA enhancer sequences
2. Activate Histone Acetyl Transferases (HAT) to loosen DNA around Histones

Overall Role:
Enhance Lymphoid and Myeloid Differentiation and Proliferation

MUTATIONS result in:
• Acute Myeloid Leukemia (AML)
• Acute Lymphoid Leukemia (ALL)

Question 8

What the prognosis of AML and ALL involving mutations that affect CBF function?

Answer 8

Good Px., these diseases are very treatable

Question 9

What 2 mutations do we need to know involving CBF that result in AML?
• Give Description of mutation effects.

Answer 9

t(8,21)
• Runx1T1 on chromosome 8 fuses with Runx1
• Runx1/Runx1T1 fusion protein still dimerizes with CBFß
• Runx1/Runx1T1-CBFß Activate Histone Deacetylases (HDACs)

inv(16)
• Chromosome 16 inverts and recombines with its homologue and CBFß/MYH11 fusion protein is created
• MYH11 a co-repressor causes the Runx1-CBFß/MYH11 gene to co-repress transcription

NET EFFECT OF BOTH:
• Myeloid and Lymphoid non-differentiation

Question 10

What mutation involving CBF causes ALL?

Answer 10

t(12,21)

•Runx1 translocates to fuse with ETV, the two work together to recruit HDAC via Runx1/ETV-CBFß heterodimer

NET EFFECT:
• Myeloid and Lymphoid non-differentiation

Question 11

What 3 genes are commonly mutated affecting DNA methylation?
• What cancer is caused by these mutations?

Answer 11

3 genes:
• DNA methyl Transferase 3A (DNMT3A) gene
• Tet1, Tet2 genes
• Isocitrated Dehydrogenase I (IDH1) gene

Acute Myeloid Leukemia

Question 12

What role do the following play in causing cancer?
• DNMT3A
• IDH1
• Tet1, and Tet2

Answer 12

DNMT3A:
• Involved in methylating and suppressing genes coding for Tyrosine Kinases such as Flt3 that are involved in PROLIFERATION

Tet1, Tet2:
• Demethylating enzymes that are involved in upregulating genes that cause DIFFERENTIATION

IDH1:
• Mutates to create alpha-HYDROXY-glutarate that inhibits Tet1, and Tet2

***OVERALL effect is proliferation of immature undifferentiated cells = AML