Colon cancer development

Question 1

Where do cancer cells in intestine are from?

Answer 1

Intestinal epithelium

Question 2

How do tissue regulate the balance between proliferation and differentiation in tussue (balanced= homeostasis)

Answer 2

By turning signaling pathways ON or OFF for different gene expression

If inbalanced: disease

Question 3

What is the first step in developing colon cancer?

Answer 3

APC mutation.
APC= adenomatour Polyposis Coli

Question 4

Explain the Wnt-signaling and the role of APC during the ON/OFF of Wnt-signaling pathway

Answer 4

Without Wnt (so inactive):
Frizzled receptor+ co-receptor LRP can’t activate protein Dishevelled. THE APC complex (APC/Axin, active GSK3/Active CK1) are able to degrade beta-catenin (phosporylated and degraded). Degraded can’t bind to LEF1/TCF TF, so no transcription of Wnt target genes

Wnt pathway ON:
Wnt protein (secreted by P-cells) bind to Frizzled and Frizzled get’s activated (together with LRP). Axin binds to Dishevelled protein, and the APC protein falls apart so no beta-catenin gets degraded. B-catenin can bind to LEF1/TCF TF, which leads to the kickoff of the protein Groucho. This will lead to transcription of Wnt target genes

Question 5

Where can Wnt signaling be found in the intestine?

Answer 5

At the bottom of the crypts. Wnt signaling is OFF at the top of the vili

Question 6

What will happen when APC is mutated?

Answer 6

Over proliferation
APC mutated: APC complex can’t stay together, leading to beta-catenin destruction complex (APC complex) cannot be formed. Therefore there will be continous accumilation of beta-catenin and transcription of Wnt target genes

Question 7

What is beta-catenin

Answer 7

Pro-oncogene; however it is a co-activator of transcription

Question 8

What is LEF/TCF

Answer 8

Transcription factor; it needs beta-catenin for activation

Question 9

What is APC

Answer 9

Tumor suppressor

Question 10

What is Frizzled

Answer 10

Receptor

Question 11

What is Wnt

Answer 11

Ligand

Question 12

How can you analyse which target genes contribute to the phenotype imposed by beta-catenin and how could you find out which target genes are activated by beta-catenin?

Answer 12

Micro-array analysis comparing gene expression in cells with: Wnt signaling/beta-cateine TVF ON/OFF
How do you create this ON/OFF situation?
For beta-catenin TCF ON:
Cancer cell lines with mutation in APC/beta-catenin –> constitutive accumulation of beta-catenin (target gene activation)
For beta-catenin TCF OFF:
Same cells manipulated to express TCF lacking the beta-catenin binding domain (no target gene activation)

Then RNA isolation, and Micro-array

Question 13

Which cells have limitless replication potential?

Answer 13

Stem cells

Question 14

Which protein is the marker for intestinal stem cells?

Answer 14

Lgr5