Signaling of Human Frizzled Receptors to the Mating Pathway in Yeast

Abstract

Frizzled receptors have seven membrane-spanning helices and are considered as atypical G protein-coupled receptors (GPCRs). The mating response of the yeast Saccharomyces cerevisiae is mediated by a GPCR signaling system and this model organism has been used extensively in the past to study mammalian GPCR function. We show here that human Frizzled receptors (Fz1 and Fz2) can be properly targeted to the yeast plasma membrane, and that they stimulate the yeast mating pathway in the absence of added Wnt ligands, as evidenced by cell cycle arrest in G1 and reporter gene expression dependent on the mating pathway-activated FUS1 gene. Introducing intracellular portions of Frizzled receptors into the Ste2p backbone resulted in the generation of constitutively active receptor chimeras that retained mating factor responsiveness. Introducing intracellular portions of Ste2p into the Frizzled receptor backbone was found to strongly enhance mating pathway activation as compared to the native Frizzleds, likely by facilitating interaction with the yeast Gα protein Gpa1p. Furthermore, we show reversibility of the highly penetrant G1-phase arrests exerted by the receptor chimeras by deletion of the mating pathway effector FAR1. Our data demonstrate that Frizzled receptors can functionally replace mating factor receptors in yeast and offer an experimental system to study modulators of Frizzled receptors.

Frizzled receptors signal through G proteins

“…We have shown that Frizzled receptors co-expressed with chimeric G proteins can activate the yeast MAPK pathway, thus confirming Frizzled as a GPCR. These results confirm those obtained by another group that expressed human Frizzled receptors 1 and 2 and observed activation of the yeast MAPK pathway through the yeast G proteins [42]. Our study extends this work by showing that there is specificity in the interaction between Frizzleds and chimeric G proteins, with Frz1, Frz2, Frz6 and Frz7 preferentially interacting with Gpa1/Gα s over Gpa1/Gα i or Gpa1/Gα q .…”

GSK-3� and Vitamin D Receptor are Involved in �-Catenin and Snail Signaling in High Glucose-Induced Epithelial-Mesenchymal Transition of Mouse Podocytes

“…However, in recent years, studies on GSK-3β and Wnt/β-catenin signaling in tumor cells suggested that inhibition of GSK-3β could both inhibit or promote Wnt/β-catenin signaling [31.] GSK-3β has two ways to modulate β-catenin, revealing that GSK-3β can negatively regulate Wnt/β-catenin signaling through degradation of β-catenin (the traditional view), but can also positively control expression of β-catenin by an even more complex regulatory mechanism [32,33].…”

International Union of Basic and Clinical Pharmacology. LXXX. The Class Frizzled Receptors

“…Human Frizzleds equipped with the N-terminal signal sequence from yeast 7TM STE2 receptor are capable of recruiting the yeast mating pathway, which requires the activation of a heterotrimeric G protein (Dirnberger and Seuwen, 2007). Even though this artificial system does not prove that FZDs can do the same in mammalian cells, it is indeed a strong indication.…”