Notch1 and its role in pre T-cell Acute Lymphoblastic Leukemia (ALL) By Rebecca Goodman

What is Acute Lymphoblastic Leukemia? A cancer caused by the proliferation of immature lymphocytes (pre T-cells and pre B-cells) A cancer caused by the proliferation of immature lymphocytes (pre T-cells and pre B-cells) These cells are non-functional and accumulate in the body, inhibiting the function of normal cells These cells are non-functional and accumulate in the body, inhibiting the function of normal cells

What does a T-cell do? T-cells are white blood cells that are responsible for cell-mediated immunity and for the coordination of the immune response T-cells are white blood cells that are responsible for cell-mediated immunity and for the coordination of the immune response

75% of Childhood Leukemias in the US are Acute Lymphoblastic Leukemia 75% of Childhood Leukemias in the US are Acute Lymphoblastic Leukemia 80% of ALL’s are in B-cell progenitor cells 80% of ALL’s are in B-cell progenitor cells 15% of ALL’s involve thymocytes 15% of ALL’s involve thymocytes 5% involve cells of unknown origin 5% involve cells of unknown origin The majority of patients with pre T-cell ALL are white males The majority of patients with pre T-cell ALL are white males

Normal Differentiation of Blood Cells All blood cells originate from Haemopoietic Stem Cells found in the bone marrow All blood cells originate from Haemopoietic Stem Cells found in the bone marrow Pike, Marilyn

Non-functional thymocytes accumulate in the bone marrow and organs and crowd out normal hemopoietic cells leading to… Leukocytosis (high white blood cell count) Leukocytosis (high white blood cell count) Bone Marrow Failure (evidenced by fatigue, pallor, bruising, hemorrhaging, infection, and fever) Bone Marrow Failure (evidenced by fatigue, pallor, bruising, hemorrhaging, infection, and fever) Infiltration of spleen, lymph nodes, skin, and CNS Infiltration of spleen, lymph nodes, skin, and CNS

ALL is diagnosed by… Physical Examination Physical Examination Complete Blood Count (CBC) Complete Blood Count (CBC) Bone Marrow Evaluation Bone Marrow Evaluation The clinical onset of ALL is generally acute and rapidly progressing.

Treatments consist of… Chemotherapy to induce a complete remission Chemotherapy to induce a complete remission Post-remission chemotherapy and radiation of the CNS to improve the duration of remission Post-remission chemotherapy and radiation of the CNS to improve the duration of remission

In the 1960’s, less that 5% of children with ALL survived more than 5 years, while today, 85% of children with ALL live five years or more after diagnosis.

Notch1 First discovered in Drosophila and C. Elegans First discovered in Drosophila and C. Elegans A transmembrane receptor A transmembrane receptor Drosophila has one notch receptor whereas humans have four Drosophila has one notch receptor whereas humans have four Highly conserved Highly conserved Ligands are Delta and Serrate/Jagged Ligands are Delta and Serrate/Jagged

Domains of Notch1 Protein Guidos, Cynthia J. Immunology

Function of Notch1 Notch signaling pathways Notch signaling pathways 1. Determine Binary Cell Fates -ex. Neuronal vs. Epidermal Cell in Drosophila 2. Affects Survival/Proliferation of Committed Progenitors -ex. Pre T-cells

Notch Pathway Guidos, Cynthia J. Immunology

Mutations in the Notch Pathway can lead to… Acute Lymphoblastic Lymphoma (Notch1) Acute Lymphoblastic Lymphoma (Notch1) CADASIL (Notch3) CADASIL (Notch3) The Alagille Syndrome (Jagged1) The Alagille Syndrome (Jagged1) HPV-induced Cervical Cancer (Notch1) HPV-induced Cervical Cancer (Notch1)

The specific mutation that leads to ALL… A translocation between chromosomes 7 (contains T-cell receptor gene) and 9 (contains Notch1 gene) A translocation between chromosomes 7 (contains T-cell receptor gene) and 9 (contains Notch1 gene) This puts part of the Notch1 gene downstream of the TCR gene promoter and leads to overexpression of the mutant Notch1 This puts part of the Notch1 gene downstream of the TCR gene promoter and leads to overexpression of the mutant Notch1

The mutant Notch1 protein has a truncated extracellular domain and is constitutively activated The mutant Notch1 protein has a truncated extracellular domain and is constitutively activated Thus, the intracellular domain will undergo proteolysis without activation by a ligand Thus, the intracellular domain will undergo proteolysis without activation by a ligand In the case of ALL this ultimately causes the thymocytes to remain undifferentiated while proliferating In the case of ALL this ultimately causes the thymocytes to remain undifferentiated while proliferating

Evidence that this Notch mutation leads to ALL Pear et al infected the bone marrow of mice with mutant Notch1 using recombinant retroviruses. This induced pre T-cell leukemia in ~50% of the animals. Pear et al infected the bone marrow of mice with mutant Notch1 using recombinant retroviruses. This induced pre T-cell leukemia in ~50% of the animals.

Steps in Lymphoblast Differentiation at which Notch1 might play a role… 1. T-cell vs. B-cell 2. Rearrangement of receptors (two fates for T-cells) 3. Decision between Helper T-cell or Cytotoxic T-cell

Guidos, Cynthia J. Immunology