Colony-Stimulating Factor Colony-Stimulating Factor ReceptorReceptor

(CSF-1R); c-fms.(CSF-1R); c-fms.

By Nate ReynoldsBy Nate Reynolds

Questions to Be AnsweredQuestions to Be Answered

What is the CSF-1 Receptor?What is the CSF-1 Receptor?

What does the CSF-1 Receptor do in the What does the CSF-1 Receptor do in the normal cell and how does it do it?normal cell and how does it do it?

What is the link between the CSF-1 What is the link between the CSF-1 Receptor and cancer?Receptor and cancer?

What is the CSF-1 Receptor?What is the CSF-1 Receptor?

It is a receptor tyrosine kinase.It is a receptor tyrosine kinase. It has 4 domains:It has 4 domains:

1)1) Extracellular domain that binds the ligandExtracellular domain that binds the ligand2)2) Membrane spanning domainMembrane spanning domain3)3) Cytoplasmic domain that has tyrosine kinase Cytoplasmic domain that has tyrosine kinase

activityactivity4)4) C-terminusC-terminus

Its ligand is macrophage colony Its ligand is macrophage colony stimulating factor (M-CSF or CSF-1).stimulating factor (M-CSF or CSF-1).

What does CSF-1 Receptor do in What does CSF-1 Receptor do in the normal cell?the normal cell?

It is responsible for regulating the growth, It is responsible for regulating the growth, proliferation, and differentiation of monocyte and proliferation, and differentiation of monocyte and macrophage precursors.macrophage precursors.

The binding of M-CSF to its receptor during G-1 The binding of M-CSF to its receptor during G-1 results in a commitment through the progression results in a commitment through the progression of DNA synthesis and cell division.of DNA synthesis and cell division.

It has also been shown to be expressed in It has also been shown to be expressed in normal trophoblast and fibroblast cells.normal trophoblast and fibroblast cells.

How does the CSF-1 Receptor How does the CSF-1 Receptor work normally?work normally?

It binds its ligand, dimerizes, It binds its ligand, dimerizes, and phosphorylates itself.and phosphorylates itself.

Its phosphorylated tyrosine Its phosphorylated tyrosine residues serve as binding sites residues serve as binding sites for other proteins via SH2 for other proteins via SH2 domains.domains.

A signal cascade is produced A signal cascade is produced culminating in mitogenesis and culminating in mitogenesis and morphological changes.morphological changes.1) Believed to activate the Ras 1) Believed to activate the Ras

pathway as well as the GTP pathway as well as the GTP binding proteins Rac and Rho. binding proteins Rac and Rho.

How does CSF-1 Receptor work How does CSF-1 Receptor work normally?normally?

Once activated the receptor is internalized Once activated the receptor is internalized and degraded.and degraded.

This is an important part of the regulation This is an important part of the regulation process; it disallows the continued process; it disallows the continued propagation of the signal.propagation of the signal.

What is the link between CSF-1 What is the link between CSF-1 Receptor and cancer?Receptor and cancer?

The gene that encodes for the CSF-1 The gene that encodes for the CSF-1 Receptor (c-fms) was found as a homolog Receptor (c-fms) was found as a homolog to v-fms, or feline sarcoma virus.to v-fms, or feline sarcoma virus.

V-fms encodes a constitutively active form V-fms encodes a constitutively active form of the receptor, resulting in increased of the receptor, resulting in increased growth and proliferation, as well as growth and proliferation, as well as changes in morphology.changes in morphology.

Understanding cancer: Differences Understanding cancer: Differences between c-fms and v-fmsbetween c-fms and v-fms

Differences between Differences between c-fms protein and v-c-fms protein and v-fms protein occur in fms protein occur in three places:three places:

1)1) The extracellular The extracellular domaindomain

2)2) The intracellular The intracellular domaindomain

3)3) The C-terminusThe C-terminus

Differences between c-fms and v-Differences between c-fms and v-fms: The extracellular domainfms: The extracellular domain

In v-fms a leucine at amino acid 301 is changed to serine.In v-fms a leucine at amino acid 301 is changed to serine.

This point mutation alone causes some transformation, but not as This point mutation alone causes some transformation, but not as much as pure v-fms.much as pure v-fms.

Likely that point mutation causes a conformational changes similar Likely that point mutation causes a conformational changes similar to the one caused by the binding of the ligand.to the one caused by the binding of the ligand.

The intracellular domainThe intracellular domain In v-fms tyrosine residue Y807 represents a major In v-fms tyrosine residue Y807 represents a major

autophosphorylation site.autophosphorylation site. Replacing this residue with phenylalanine in the v-fms Replacing this residue with phenylalanine in the v-fms

gene resulted in no change in cell growth or proliferation.gene resulted in no change in cell growth or proliferation. It did impact morphology, reverting the cells back to their It did impact morphology, reverting the cells back to their

untransformed state. untransformed state.

The intracellular domainThe intracellular domain

When phosphorylated Y807 interacts with p120RasGap When phosphorylated Y807 interacts with p120RasGap and p190RhoGap.and p190RhoGap.

Interaction with and phosphorylation of p120RasGap is Interaction with and phosphorylation of p120RasGap is an important step in the cascade of events leading to the an important step in the cascade of events leading to the breakdown of the actin cytoskeleton.breakdown of the actin cytoskeleton.

The C-terminusThe C-terminus

The C-terminus of c-fms The C-terminus of c-fms contains 40-50 amino contains 40-50 amino acids depending on the acids depending on the species; the v-fms protein species; the v-fms protein contains 11 different contains 11 different residues.residues.

A chimera of c-fms and A chimera of c-fms and the v-fms C-terminus the v-fms C-terminus does not transform cells does not transform cells in the absence of the in the absence of the ligand, M-CSF 1.ligand, M-CSF 1.

The C-terminusThe C-terminus

The C-terminus is a negative regulator, likely involved in The C-terminus is a negative regulator, likely involved in the internalization, ubiquitination, and degradation of the the internalization, ubiquitination, and degradation of the CSF-1 Receptor.CSF-1 Receptor.

Autophosphorylation of Tyr 973 in the C-terminus region Autophosphorylation of Tyr 973 in the C-terminus region allows binding of c-Cbl, which leads to ubiquitination and allows binding of c-Cbl, which leads to ubiquitination and degradation.degradation.

Putting it together . . .Putting it together . . .

Point mutations in the extracellular domain can Point mutations in the extracellular domain can change the protein’s conformation to a change the protein’s conformation to a constitutively active form.constitutively active form.

Once activated autophosphorylation of tyrosine Once activated autophosphorylation of tyrosine residues in the intracellular domain can affect residues in the intracellular domain can affect changes in morphology.changes in morphology.

The C-terminus acts as a negative regulator.The C-terminus acts as a negative regulator. A combination of mutations leads to the most A combination of mutations leads to the most

transformed cells.transformed cells.

CSF-1 Receptor and Cancer: More CSF-1 Receptor and Cancer: More than a question of mutationsthan a question of mutations

In humans CSF-1 Receptor is over-In humans CSF-1 Receptor is over-expressed in certain types of cancer:expressed in certain types of cancer:

1)1) Ovarian epithelial carcinomasOvarian epithelial carcinomas

2)2) Endometrial carcinomasEndometrial carcinomas

3)3) Mammary carcinomasMammary carcinomas

4)4) Various leukemiasVarious leukemias

Regulation of c-fmsRegulation of c-fms

The c-fms gene is under the control of two The c-fms gene is under the control of two separate promoters, yielding two mRNA separate promoters, yielding two mRNA isoforms but identical proteins.isoforms but identical proteins.

Promoter 1 is active in placental cells and Promoter 1 is active in placental cells and promoter 2 is active in macrophages.promoter 2 is active in macrophages.

These promoters are abnormal (lacking These promoters are abnormal (lacking TATTA-box elements and GC rich TATTA-box elements and GC rich regions).regions).

The regulation of c-fms is still enigmatic. The regulation of c-fms is still enigmatic.

To conclude . . .To conclude . . .

Despite a lack of knowledge about the Despite a lack of knowledge about the regulation of the c-fms gene, the presence regulation of the c-fms gene, the presence of v-fms provides hope for cell-specific of v-fms provides hope for cell-specific therapies.therapies.

V-fms gives clues as to what regions of the V-fms gives clues as to what regions of the c-fms protein are important for both c-fms protein are important for both morphological transformation and morphological transformation and mitogenesis.mitogenesis.