During growth, unicellular D. discoideum monitor their cell density relative to that of their bacterial food source by secreting a glycoprotein called prestarvation factor at a constant rate.

TLS Online TPP Program

#Id: 1571

#Unit 4. Cell Communication and Cell Signaling

In the absence of Wnts,

β-catenin is bound in a complex with Axin (a scaffold protein), APC, and kinases CK1 and GSK3.

TLS Online TPP Program

#Id: 1572

#Unit 4. Cell Communication and Cell Signaling

Kinases CK1 and GSK3,

sequentially phosphorylate β-catenin at multiple serine and threonine residues.

TLS Online TPP Program

#Id: 1573

#Unit 4. Cell Communication and Cell Signaling

The E3 TrCP ubiquitin ligase then binds to two phosphorylated β-catenin residues, leading to β-catenin ubiquitinylation and degradation in proteasomes.

TLS Online TPP Program

#Id: 1574

#Unit 4. Cell Communication and Cell Signaling

Binding of Wnt to its receptor Frizzled (Fz) and to the LRP co-receptor triggers phosphorylation of LRP by GSK3 and CK1, enables Axin to bind LRP & Dsh.

 

TLS Online TPP Program

#Id: 1575

#Unit 4. Cell Communication and Cell Signaling

Binding of Axin to the phosphorylated LRP protein and to Dishevelled disrupts the Axin–APC–CK1–GSK3–β-catenin complex. 

TLS Online TPP Program

#Id: 1576

#Unit 4. Cell Communication and Cell Signaling

Unphosphorylated β-catenin translocates to the nucleus.