Antagonistic regulation of F-BAR protein assemblies controls actin polymerization during podosome formation

Abstract

Summary FBP17, an F-BAR domain protein, has emerged as a crucial factor linking the plasma membrane to WASP-mediated actin polymerization. Although it is well established that FBP17 has a powerful self-polymerizing ability that promotes actin nucleation on membranes in vitro, knowledge of inhibitory factors that counteract this activity in vivo is limited. Here, we demonstrate that the assembly of FBP17 on the plasma membranes is antagonized by PSTPIP2, another F-BAR protein implicated in auto-inflammatory disorder. Knockdown of PSTPIP2 in macrophage promotes the assembly of FBP17 as well as subsequent actin nucleation at podosomes, resulting in an enhancement of matrix degradation. This phenotype is rescued by expression of PSTPIP2 in a manner dependent on its F-BAR domain. Time-lapse total internal reflection fluorescence (TIRF) microscopy observations reveal that the self-assembly of FBP17 at the podosomal membrane initiates actin polymerization, whereas the clustering of PSTPIP2 has an opposite effect. Biochemical analysis and live-cell imaging show that PSTPIP2 inhibits actin polymerization by competing with FBP17 for assembly at artificial as well as the plasma membrane. Interestingly, the assembly of FBP17 is dependent on WASP, and its dissociation by WASP inhibition strongly induces a self-organization of PSTPIP2 at podosomes. Thus, our data uncover a previously unappreciated antagonism between different F-BAR domain assemblies that determines the threshold of actin polymerization for the formation of functional podosomes and may explain how the absence of PSTPIP2 causes auto-inflammatory disorder.

Defining Mononuclear Phagocyte Subset Homology Across Several Distant Warm-Blooded Vertebrates Through Comparative Transcriptomics

“…The conserved cDC1 signature encompasses genes with known contribution in the biology of this lineage, such as XCR1 , FLT3 , and CADM1 (59), as well as additional genes which biological function in this subset remains enigmatic, such as the germinal center B-cell-expressed transcript 2 protein ( GCET2 ), the WDFY family member 4 ( WDFY4 ) whose polymorphism is associated to autoimmune diseases (62), and two intracellular trafficking proteins, a formin-binding protein ( FNBP1 ) (63) and Sorting Nexin-22 ( SNX22 ) (64) (Table 1). The conserved cDC1 vs. (pDC and cDC2) relative signature provides a longer list of genes belonging to an interaction network that includes BCL6 , a transcriptional repressor that was recently found involved in the specification of cDC1 (17) as well as XCR1 and CALM1 (Figure 9E).…”

CSF-1 Receptor Signaling in Myeloid Cells

“…PSTPIP2 is tyrosine phosphorylated within 30 sec and inhibits actin polymerization and the ruffling response (Chitu et al 2005). By competing with other F-BAR family proteins for phosphatidylinositol 4,5-bisphosphate (PIP2)-rich membrane-binding sites and recruiting PTPN12 to those sites, PSTPIP2 may mediate the local dephosphorylation and par-tial inactivation of WASP (Cote et al 2002;Tsujita et al 2013).…”

Dynamic Shaping of Cellular Membranes by Phospholipids and Membrane-Deforming Proteins

“…Some BAR family proteins act as tumor suppressors. F-BAR-only protein, PSTPIP2, antagonizes actin polymerization in the podosome by competing with FBP17 at the membrane (302). Furthermore, the I-BAR containing protein MIM is present in normal tissues, but is missing in several metastatic cell lines, and this downregulation is associated with the progression of bladder transitional carcinomas (316).…”