Frizzled class receptor 1 (also known as FZD1) belongs to the frizzled subfamily of G protein-coupled receptors. Currently, the frizzled family of GPCRs contains 10 frizzled proteins (FZD1-10) and Smoothened (SMO).

Similar to other GPCRs, FZD1 consists of a single polypeptide with an extracellular N-terminus, an intracellular C-terminus, seven hydrophobic transmembrane domains (TM1-TM7) linked by three extracellular loops (ECL1-ECL3) and three intracellular loops (ICL1-ICL3). FZD1 is encoded by the firzzled-1 gene which is mainly expressed in the adult heart, placenta, lung, kidney, pancreas, prostate and ovary.

FZD1 is activated by WNTs, which are cysteine-rich lipo-glycoproteins with fundamental functions in ontogeny and tissue homeostasis. Signaling through the WNT/FZD complex can lead to the activation of pertussis toxin-sensitive heterotrimeric G proteins, the elevation of intracellular calcium activation of cGMP-specific PDE6 and elevation of cAMP as well as RAC-1, JNK, Rho and Rho kinase signaling¹.

The relation between the FZD1 pathway and various pathologies has been researched extensively. Reduced levels of FZD1 can be found in the spinal cords of ALS transgenic mice, possibly due to the increase of FZD1 protein degradation or the inhibition of FZD1 protein expression in the spinal cord in the disease process of ALS transgenic mice². The FZD1 signaling pathway has also been implicated in inflammatory bowel disease. Patients with ulcerative colitis exhibit reduced expression of FZD1. FZD1 is overexpressed in the multi drug resistant cancer cell subline MCF-7/ADM and seems to mediate multidrug resistance by regulating the Wnt/β-catenin pathway³.