The Notch signaling pathway is a cell signaling system that regulates cell proliferation, differentiation, and death. It relies on protein-protein interactions between Notch receptors on receiving cells and ligands on sending cells. Faulty Notch signaling is implicated in cancers like T-ALL and diseases like CADASIL. The pathway involves cleavage of the Notch receptor which releases the Notch intracellular domain to regulate target gene expression. Inhibitors of gamma secretase can inhibit the pathway and prevent cancer overexpression of Notch.

1. NOTCH PATHWAY
GROUP 1.2.6

2. GROUP MEMBERS
NAME REGISTRATION NUMBER
KAALE SHARON 2019-08-07612
WAJAMBUKA FAISAL 2020-08-00012
EDYEGU CHRISTOPHER 2020-08-00025

3. Introduction.
• The notch pathway is a cell signaling system that relies on protein –
protein interactions to transduce signals.
• It regulates cell proliferation, cell fate, differentiation and cell death in
all metazoans.
• The notch pathway is a highly conserved cell signaling pathway

4. Aim of studying NOTCH pathway.
• NOTCH signaling is dysregulated in many cancers and faulty NOTCH
signaling is implicated in many diseases forexample CADASIL, Alagille
syndrome.

5. Importance of the NOTCH pathway.
• Promotes proliferative signaling during neurogenesis.
• Stabilization of arterial endothelial fate and angiogenesis.
• Determination of fate of cells in the immune system
• Plays a major role in regulation of embryonic development.

6. Components of the notch pathway
a. Notch receptors; NOTCH 1, NOTCH 2, NOTCH 3, NOTCH 4
These are hetero-oligomers made of three components
-notch extracellular domain (NECD).
-notch intracellular domain (NICD).
-transmembrane component.
b. Ligands which include the jagged protein family (JAG 1 and JAG 2)
and the delta like protein family (DLL 1, DLL 3, DLL 4).

7. Mechanism.

8. Mechanism.
• The notch pathway requires two cells; a sending cell which has more
ligands than notch receptors and a receiving cell which has more
notch receptors than ligands.
• For notch signaling to be activated, the ligand has to bind to the
NECD.
• The ligands is activated first by a protein(Neur or Mib) within the
sending cell that ubiquinates the ligand in order to activate it.

9. • In the golgi apparatus (S1 cleavage), furin in its future extracellular
domain converts it into heterodimer and its then transported to the
cell surface receptor consisting of three domains, signalling starts
when the ligand interacts with the receptor leading to further
cleavages.
• Endocytosis of the ligand promotes exposure of the NRR domain
(negative regulatory region domain) of the receptor for S2 cleavage.
• Once activated the ligand can then bind on the NECD.

10. • A protease(ADAM) then cleaves the NECD dislodging it from the receiving
cell, a process known as S2 cleavage.
• Secretase gamma cleaves the NICD off the receptor, a process known as S3
cleavage.
• Once NICD is free in the cytosol it can bind to a complex of proteins that
then translocate into the nucleus .
• This leads to transcription of NOTCH target genes eg; Myc, P21, Cyclin D3.

11. • Once target genes have been expressed, NICD can be be down-
regulated via an E3 ubiquinine ligase(FBW 7).
• FBW 7 ubiquinates the NICD which leads to degradation of the NICD
shutting down the pathway.

12. Regulation of the pathway
• Signal down regulation.
During transcription activation, NICD is phosphorylated on its PEST
domain by kinases such as CDK8 and targeted for proteasomal degradation
by E3 ubiquitin ligases such as sel10/Fbw7. This terminates the notch signal
and resets the cell for the next round of signaling.
Transcriptional switch and target gene expression.
In the absence of NICD, the DNA binding protein is bound to a
ubiquitous co repressor protein and histone deacetylases to repress
transcription of target genes and when NICD enters the nucleus and binds to
CSL, it triggers a conformational change which causes displacement of
repressors.

13. Inhibitors of the NOTCH pathway.
• The NOTCH pathway inhibitors can act as cancer treatments since
they can prevent over expression of NOTCH receptors and ligands
during cancer.
• Examples include;
• gamma secretase inhibitors AL101 and AL102.
• Anti-notch 1 or anti delta like monoclonal antibodies. These prevent
over expression of the NOTCH receptors and ligands.

14. • NOTCH signaling pathway plays an oncogenic role in T-ALL, lung
adenocarcinoma, splenic marginal zone lymphoma, B chronic
lymphocytic leukemia, ovarian cancer.
• NOTCH signaling pathway plays a tumor suppressing role in squamous
cell cancers, neuroendocrine tumors, pancreatic ductal
adenocarcinoma

15. NOTCH signaling in cancers
Cancer type Involved NOTCH components
T-ALL NOTCH 1, NOTCH 3
Splenic marginal zone lymphoma NOTCH 1, NOTCH 2
B chronic lymphocytic leukemia NOTCH 1-2, JAG 1-2
Lung adenocarcinoma NOTCH 1, NOTCH 3
Breast cancer NOTCH 1, NOTCH 4, JAG 1
Neuroendocrine tumors NOTCH 1, DLL3
Squamous cell cancers NOTCH 1-3

16. Disorders associated with faulty NOTCH
signaling pathway.
• Alagille syndrome.
This is an autosomal dominant genetic disease. It is caused by
abnormal NOTCH signaling with JAG 1 mutations being
predominant(greater than 90%) and NOTCH 2 mutations being second
most.
• CADASIL.
It is mediated by dominant mutations in the NOTCH 3 gene.

17. Abbreviations
• ADAM- A disintegrin and metalloproteinase
• MAML- Mastermind like proteins
• CSL- CBF-1/ suppressor of hairless/ Lag 1
• CBF-1 – Centromere Binding Factor 1
• LAG 1 – Longevity Assurance Gene 1
• RBPJ- Recombinant signal binding protein of immunoglobulin kappa J
• Neur – Neuralized
• Mib- Mindbomb

18. Abbreviations
• CADASIL – Cerebral Autosomal Dominant Arteriopathy with Subcortical
Infarcts and Leukoencepthalopathy.
• T-ALL – T cell Acute Lymphoblastic Leukemia.
• PEST domain is a sequence motif found in some proteins that are targeted
for rapid degradation within the cell. (PEST is P- proline, E- glutamic acid, S-
serine, T- threonine)

19. Corrections
• Who was Alagille?
Daniel Alagille was a French physician who specialized in paediatric
hepatology, the study of childhood liver diseases.
How breast cancer and lung adenocarcinoma is related to NOTCH
signaling?
In lung adenocarcinoma, there is high expression of NOTCH 1 and
NOTCH 3. This alteration involves loss of NUMB expression( a negative
modulator of NOTCH signaling) which increases NOTCH activity and gain of
function mutations of NOTCH 1 gene.
in breast cancer, upregulation of non mutated JAG 1 and NOTCH 1 is
associated with poor regulation of breast cancer. The mutations of NOTCH 1
and NOTCH 4 promote epithelial mammary tumorigenesis.

20. • How does NOTCH signaling pathway play an oncogenic role?
The NOTCH signaing pathway is a regulator of self renewal and differentiation in
several tissues and cell types. Hyperactivity of the NOTCH signaling pathway
brings about excessive uncontrolled cellular proliferation leading to tumors.
For example mutations that abolish FBW 7 function in the pathway can lead to
cancers since there will be no stopping of the pathway.

21. References.
• Robbins and Cotran Pathological basis of disease 9th edition.
• Binghan Zhou, Wanling Lin, Yaling long, Yunkai yang, Huan Zhang,
Kongming Wu, Qian Chu. Notch signaling pathway: architecture,
disease, and therapeutics. 2022