12 - Cell Signalling & Cancer

Which of the following are TRUE about signaling pathways?

A) Binding to GTP can act as a “switch” to turn on activity of some proteins

B) Hormones are typically examples of endocrine signaling

C) Paracrine signaling requires cell-to-cell contact

D) Juxtacrine signaling involves secretion of ligands into the bloodstream

E) A morphogen is a signaling factor that influences cell fate in a concentration-dependent manner

a b e

Cancer:

a group of diseases of abnormal, uncontrolled cell division

Malignant:

cells invade nearby tissue and can spread to other parts of the body

Benign:

Abnormal growth without invasion

Metastasis:

cancer cells spread and form tumours at additional sites in the body

Transformation:

process of a normal cell becoming cancerous

• Primary tumor:

• The original tumor where abnormal growth begins.
  
  

All malignant cancers are driven by

mutations in DNA

Oncogenes

contain gain-of-function mutations that turn on pathways promoting processes that drive growth and survival of cancer cells

T/F Increasing speed of GTP hydrolysis = increased Ras signalling?

false

Tumor suppressor

genes typically contain loss-of-function mutations that remove a protein that usually functions to limit one of these cancer promoting processes

Phosphorylation

addition of a phosphate group, typically on serine, threonine, or tyrosine residues.

“Molecular switches” in signal transduction: Phosphorylation

Often (though not always) phosphorylation is used to activate a signaling protein/pathway. This is common for turning on cellular responses like proliferation or migration

In cancer, do you think deletion/nonfunctional mutants occur more commonly in kinases or phosphatases?

phosphatases; loss of function in phosphatases can lead to unchecked signalling, which can promote cancer progession

Which of the techniques discussed in this course would help you identify changes in expression (mRNA or protein) and/or mutations in kinases and phosphatases?

rna seq and 2d gel electrophoresis

Src is auto-inhibited when

the SH2 domain is bound to phosphorylated tyrosine 527.

Src is active when

other proteins compete for SH2/SH3 binding and when the activation loop tyrosine 416 is phosphorylated

What types of mutations in Src (or other changes in cancer cells) could cause an increase in Src kinase activity?

A) A point mutation that changes tyrosine 527 to phenylalanine

B) A point mutation that changes tyrosine 416 to phenylalanine

C) A mutation in the linker sequence prevents binding to SH3

D) A mutation in another signaling protein creates an over abundance of tyrosine-phosphorylated Src-binding proteins

E) A nonsense mutation occurs shortly after (C-terminal side) the coding sequence for the kinase domain

F) A nonsense mutation occurs shortly before (N-terminal side) the coding sequence for the kinase domain

a c d e

Western blot

detect specific protein(s) using specific antibody

how could a western blot be used to study protein levels and cell signaling

Can detect:

Total protein levels (e.g. total Akt)

Phosphorylation-specific forms of proteins (e.g. phospho-Tyrosine for active RTKs)

Allows you to study changes in signaling pathways, e.g. activation of Src, EGFR, etc., by comparing protein levels between conditions (cancer vs. normal).

Effects of oncogene signalling

multiple signalling pathways are involved, and that these converge on pathways related to cancer progression:

• Survival & growth

• Cell motility (to travel around the body to make tumors at other sites; metastasis)

• Angiogenesis (making the tumor’s blood supply)

activation mechanisms of RTKs (EGFR)

activation mechanisms of ligand-gated channels (LGCs)

activation mechanisms of GPCRs

activation mechanisms of non-receptor kinases (Src)

activation mechanisms of GTPases (Kras)