8. Developmental pathways and cancer (Notch+JAgged)

Developmental pathways are cellular signaling routes crucial for normal development. In cancer, they are often targeted by viruses and are associated with tumor development, progression, and chemoresistance. They are important for diagnosis and as targets for therapy, especially in hematological tumors.

The Notch family in mammals consists of four highly conserved transmembrane receptors (Notch-1, 2, 3, and 4) and five ligands. These are large single-pass type I transmembrane proteins involved in cell fate decisions.

Most cancer-associated mutations in Notch receptors occur in the intracellular domain, which is a recurrent site of mutations.

Notch signaling is activated through close proximity between a signal-sending cell (expressing the ligand) and a signal-receiving cell (expressing the receptor). Activation involves consecutive cleavage by metalloprotease and gamma-secretase enzymes.

Gamma-secretase is an enzyme that cleaves the Notch receptor, releasing its intracellular domain to act as a transcription factor. Malfunction of gamma-secretase is linked to Alzheimer's disease.

FBXW7 is involved in the poly-ubiquitination of Notch, serving as a mechanism to shut down Notch signaling.

Notch signaling is involved in neuronal development, differentiation of haemogenic endothelial cells into hematopoietic stem cells, commitment of immune cells, vasculogenesis, arteriogenesis, and wound healing.

• Congenital heart disease (Notch1 loss-of-function)
• Alagille syndrome (Jag1 or Notch2 loss-of-function)
• CADASIL (Notch3 loss-of-function)
• Hajdu-Cheney syndrome (Notch2 gain-of-function)

CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy) is a hereditary cerebrovascular disease primarily involving loss-of-function mutations in the Notch3 gene.

Main features include recurrent subcortical ischemic events, cognitive impairment, dementia, migraine with aura, mood disturbance, and apathy.

CADASIL mutations cluster in the extracellular domain of the Notch3 receptor, especially in exons 3 and 4.

The pathological hallmark is the thickening of the arterial wall and the presence of granular osmiophilic material (GOM) near smooth muscle cells and pericytes in brain and skin arteries.

CADASIL can be diagnosed by detecting characteristic mutations in the Notch3 gene and by identifying granular osmiophilic material in skin or brain vessel biopsies.

Alagille syndrome is a rare pediatric disease associated with loss-of-function mutations in the Jag1 ligand gene, leading to hepatic failure, reduced bile duct formation, growth delay, and characteristic facial features.

Notch signaling regulates the formation and remodeling of blood vessels, particularly through the interaction of Notch receptors and ligands (e.g., DLL4) with VEGF. In tumors, this pathway is hijacked to promote abnormal, inefficient vasculature that supports tumor growth. p.4-5

DLL4 is a Notch ligand expressed in small arteries and capillaries, playing a key role in controlling tip/stalk cell behavior during angiogenesis, especially in tumor vasculature.

Anti-angiogenic therapies use monoclonal antibodies (e.g., bevacizumab) to block VEGF and experimental agents to inhibit Notch signaling, aiming to reduce tumor vascularization and growth.

In skin, Notch promotes keratinocyte differentiation and survival. In cervical cancer, HPV downregulates Notch, impairing differentiation and promoting proliferation, contributing to carcinogenesis. p.5-6

HPV oncoproteins (E6/E7) downregulate Notch1, blocking pro-differentiative pathways and promoting proliferation, transformation, and resistance to cell death in cervical cancer. p.5-6

Mutations in Notch1 and Notch3 are associated with T cell acute lymphoblastic leukemia (T-ALL), influencing disease progression and prognosis. p.7-8

B cell neoplasms express B cell markers (e.g., CD19, CD20), while T cell neoplasms express T cell markers (e.g., CD3, CD4, CD8). Molecular analysis is required for precise diagnosis.

Common features include splenomegaly, enlarged lymph nodes, mediastinal thymic masses, and possible CNS involvement.

The SDF1-CXCR4 system drives the migration of leukemic cells from the thymus to the bone marrow, promoting disease progression. Blocking CXCR4 can prevent bone marrow colonization.

Specific miRNAs released by tumoral cells can be monitored in peripheral blood (liquid biopsy) to study disease progression and response to therapy.

Although many clinical trials are ongoing (e.g., monoclonal antibodies, gamma-secretase inhibitors, SERCA inhibitors, HDAC inhibitors), there are currently no approved targeted therapies for Notch signaling in cancer.

These models allow researchers to study disease mechanisms, test drug efficacy and toxicity, and translate findings to human disease, aiding in the development of diagnostic methods and treatments.

Molecular diagnosis (e.g., Notch receptor mutations, miRNA profiles) is crucial for disease classification, prognosis, and guiding personalized therapy in hematological malignancies.

Metalloprotease is one of the enzymes responsible for the cleavage of the Notch receptor, which is necessary for activating the signaling pathway.

Notch signaling is important for the maintenance and commitment of hematopoietic stem cells, influencing the development of various immune cells.

EGF-like repeats are repetitive sequences in the extracellular domain of Notch3. Mutations in these repeats are characteristic of CADASIL and are diagnostic for the disease.

Notch3 mutations lead to the accumulation of non-functional receptors, causing thickening of the arterial wall and morphological alterations in vascular smooth muscle cells and pericytes.

Notch signaling is associated with tumor relapse and chemoresistance, making tumors difficult to treat and contributing to disease progression.

Notch signaling is required for neoangiogenesis during wound healing, promoting the formation of new blood vessels.

VEGF acts upstream of Notch during arterial-venous differentiation, and there is a negative feedback loop between the two pathways in angiogenesis.

Notch promotes the commitment of keratinocytes to differentiation and increases their survival, playing a dual role in skin homeostasis and cancer.

HPV downregulates Notch1, impairing differentiation and promoting abnormal cell growth, transformation, and resistance to cell death in cervical cancer.

Acute leukemia arises from bone marrow precursors and is associated with the circulation of immature cells, while chronic leukemia involves more mature cells and has a slower progression.

The transition from double negative (CD4-, CD8-) to double positive (CD4+, CD8+) stages is crucial in T cell development. Blockage at these stages is associated with T-ALL.

Remission is monitored by the reduction of T lymphoblasts in the bone marrow and the disappearance of dysregulated gene expression (e.g., Notch3, pTalfa).

HDAC inhibitors modulate transcription and are being studied as potential therapies to prevent the development of cancers involving Notch signaling.

Personalized therapy tailors treatment to the individual patient's molecular and clinical profile, improving efficacy and reducing side effects.