Filamin-interacting proteins, Cfm1 and Cfm2, are essential for the formation of cartilaginous skeletal elements

Abstract

Mutations of Filamin genes, which encode actin-binding proteins, cause a wide range of congenital developmental malformations in humans, mainly skeletal abnormalities. However, the molecular mechanisms underlying Filamin functions in skeletal system formation remain elusive. In our screen to identify skeletal development molecules, we found that Cfm (Fam101) genes, Cfm1 (Fam101b) and Cfm2 (Fam101a), are predominantly co-expressed in developing cartilage and intervertebral discs (IVDs). To investigate the functional role of Cfm genes in skeletal development, we generated single knockout mice for Cfm1 and Cfm2, as well as Cfm1/Cfm2 double-knockout (Cfm DKO) mice, by targeted gene disruption. Mice with loss of a single Cfm gene displayed no overt phenotype, whereas Cfm DKO mice showed skeletal malformations including spinal curvatures, vertebral fusions and impairment of bone growth, showing that the phenotypes of Cfm DKO mice resemble those of Filamin B (Flnb)-deficient mice. The number of cartilaginous cells in IVDs is remarkably reduced, and chondrocytes are moderately reduced in Cfm DKO mice. We observed increased apoptosis and decreased proliferation in Cfm DKO cartilaginous cells. In addition to direct interaction between Cfm and Filamin proteins in developing chondrocytes, we showed that Cfm is required for the interaction between Flnb and Smad3, which was reported to regulate Runx2 expression. Furthermore, we found that Cfm DKO primary chondrocytes showed decreased cellular size and fewer actin bundles compared with those of wild-type chondrocytes. These results suggest that Cfms are essential partner molecules of Flnb in regulating differentiation and proliferation of chondryocytes and actin dynamics.

NUSAP1 promotes invasion and metastasis of prostate cancer

“…FAM101B is a filamin binding protein that is upregulated by TGFβ1, participates in skeletal development, and is involved in cell shape remodeling during the epithelial to mesenchymal transition [33, 34]. Since FAM101B is involved in pathways involved in cancer cell invasion and metastasis, we wondered if FAM101B might play a role downstream of NUSAP1 in making prostate cancer cells more aggressive.…”

“…We find that NUSAP1 has limited effects on proliferation, but rather is associated with development of metastatic disease, possibly through modulation of expression of FAM101B . FAM101B is involved in cell shape remodeling during the epithelial to mesenchymal transition and is a signaling effector of TGFβ1 [33, 34], which promotes invasion and metastatic spread during prostate tumor progression [35]. …”

Refilins are short-lived Actin-bundling proteins that regulate lamellipodium protrusion dynamics

“…Deleterious mutations in Filamin genes cause a wide range of muscular dystrophies and developmental malformations in the heart, skeleton and brain (Krakow et al, 2004; Lu et al, 2007; Robertson et al, 2003). Mice with loss of a single Refilin ( Cfm , FAM101 ) gene displayed no overt phenotype (Hirano et al, 2005; Mizuhashi et al, 2014), whereas Refilin double-knockout (KO) mice showed skeletal malformations resembling those of FilaminB (FLNB)-deficient mice (Mizuhashi et al, 2014). This points to functional redundancies between RefilinB (also called Cfm1 or FAM101B) and RefilinA (also called Cfm2 or FAM101A) and suggests essential functions of the Refilin/Filamin complex during embryonic development.…”

Genome‐wide compound heterozygosity analysis highlighted 4 novel susceptibility loci for congenital heart disease in Chinese population

“…CFM2 encodes a 204 amino acid protein of an unknown function in vivo. Using a yeast 2‐hybrid screen system, Mizuhashi et al found that several independent clones encoding Flna interacted with the Cfm2 bait . And of note, mutations in the FLNA gene resulted in severe cardiac structural defects involving ventricles, atria and outflow tracts (OFTs) .…”