Formins in Human Disease

Abstract

Almost 25 years have passed since a mutation of a formin gene, DIAPH1, was identified as being responsible for a human inherited disorder: a form of sensorineural hearing loss. Since then, our knowledge of the links between formins and disease has deepened considerably. Mutations of DIAPH1 and six other formin genes (DAAM2, DIAPH2, DIAPH3, FMN2, INF2 and FHOD3) have been identified as the genetic cause of a variety of inherited human disorders, including intellectual disability, renal disease, peripheral neuropathy, thrombocytopenia, primary ovarian insufficiency, hearing loss and cardiomyopathy. In addition, alterations in formin genes have been associated with a variety of pathological conditions, including developmental defects affecting the heart, nervous system and kidney, aging-related diseases, and cancer. This review summarizes the most recent discoveries about the involvement of formin alterations in monogenic disorders and other human pathological conditions, especially cancer, with which they have been associated. In vitro results and experiments in modified animal models are discussed. Finally, we outline the directions for future research in this field.

Keywords: actin; cancer; developmental defects; formins; gene variants; genetic disease.

Figure 1

The human formin family. (A) Tree of human formins. The FH2 domain sequence of the formins was aligned with BLAST and the alignment was used to construct the tree [103]. The UniProt accession numbers of the corresponding sequences were: DIAPH1 (O60610), DIAPH2 (O60879), DIAPH3 (Q9NSV4), DAAM1 (Q9Y4D1), DAAM2 (Q86T65), FMNL1 (O95466), FMNL2 (Q96PY5), FMNL3 (Q8IVF7), FHOD1 (Q9Y613), FHOD3 (Q2V2M9), FMN1 (Q68DA7), FMN2 (Q9NZ56), INF2 (Q27J81), FHDC1 (Q9C0D6) and Delphilin (A4D2P6). (B) Structure and regulation of Diaphanous-related formins. The interaction of the DID and the DAD maintains the formin in a closed, inactive conformation. The binding of a specific GTP-loaded Rho GTPase to the N-terminal region of the formin opens the molecule, rendering it in its active form. The FH1 domain recruits profilin, which feeds the FH2 domain with G-actin to form the actin filaments. The illustrated molecules are not drawn to scale.

Figure 2

Pathogenic mutations of the formins causing monogenic disorders. Depending on the specific mutation, some formins produce different disorders. In these cases, we used the colors, as indicated, to refer to each of the diseases and the corresponding mutations. *, stop codon. The mutations without reported familial studies are indicated in italics.

Figure 3

Some of the organs and cell types affected by formin alterations. (A) The formins involved in human disorders and the affected organs and systems are indicated in the schematic of the human body. Those causing monogenic disorders are highlighted in bold. (B) Some of the affected cell types. Their most characteristic structures are indicated.

Figure 4

Schematic of a migrating cancer cell. The processes and cell functions that can be altered by aberrant expression of formins in cancer cells are indicated. Cells, such as cancer-associated fibroblasts and immune system cells, in the surroundings of the cancerous cell influence cancer progression.