The goal of project is to understand the molecular mechanisms by which mutations in INF2 cause focal segmental glomerulosclerosis (FSGS) in humans. More than 45 different FSGS-associated mutations have been identified. A subset of people with FSGS-causing INF2 mutations also exhibit Charcot Marie Tooth disease. INF2 is unique for a formin family member in that it accelerates both actin polymerization and depolymerization. Formins can autoinhibit their own activity by an intramolecular interaction between two domains, the N-terminal DID (diaphanous inhibitory domain) and the C-terminal DAD (diaphanous autoregulatory domain). INF2 has two major splice variants, one of which is associated with the endoplasmic reticulum, INF2-CAAX, and a second isoform, INF2-nonCAAX, that helps maintain Golgi integrity. INF2-CAAX is the major podocyte isoform. During the last period of this grant, we made significant progress in our understanding of both INF2 biology and how INF2 function is altered by mutations. We now understand the role INF2 plays in organelle function, and have a clearer understand of its role in regulating mitochondrial fission. We have identified a major mechanism of inhibition of INF2 activity, an interaction with an endogenous protein complex (cyclase-associated protein bound to actin that is post-translationally acetylated). We have also found that the INF2 protein undergoes cleavage at a site between the N-terminal DID region and the C-terminus, containing the FH2 and DAD regions, which may be important in regulating INF2 function and perhaps disinhibiting the functions of both regions of the protein. We have found that INF2 undergoes a cleavage event that may be important in regulating INF2 function The fact that in contrast to essentially all other actin regulatory proteins, INF2-DID mutations are a relatively common form of inherited FSGS, suggests that INF2-DID possesses unique and non-redundant functions in the podocyte. Our long-term goal is to understand these functions and, ultimately, exploit them for therapeutic benefit. We have four major goals: (1) Define the specific biochemical effects of FSGS-causing mutants. We will test the effects of multiple FSGS mutants on the interaction of INF2 with the endogenous inhibitory complex and examine INF2 mutant interactions with its binding partners; (2) Define INF2 function and mutation-mediated dysfunction in cells. This includes examination of how INF2 mutations alter its regulation of mitochondrial function; (3) Define the function of INF2 cleavage; (4) Use genetically engineered mice to better understand INF2 function and mutation mediated dysfunction in vivo.

Public Health Relevance

Mutations in the INF2 gene cause kidney disease in humans. Many different changes in this gene cause the filtering units of the kidney, the glomeruli, to function improperly. A better understanding of how defects in this gene cause human disease will have significant and direct implications for understanding both rare and common forms of kidney disease.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
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Pathobiology of Kidney Disease Study Section (PBKD)
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Abbott, Kevin C
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Beth Israel Deaconess Medical Center
United States
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Chakrabarti, Rajarshi; Ji, Wei-Ke; Stan, Radu V et al. (2018) INF2-mediated actin polymerization at the ER stimulates mitochondrial calcium uptake, inner membrane constriction, and division. J Cell Biol 217:251-268
Subramanian, Balajikarthick; Sun, Hua; Yan, Paul et al. (2016) Mice with mutant Inf2 show impaired podocyte and slit diaphragm integrity in response to protamine-induced kidney injury. Kidney Int 90:363-372
Ji, Wei-ke; Hatch, Anna L; Merrill, Ronald A et al. (2015) Actin filaments target the oligomeric maturation of the dynamin GTPase Drp1 to mitochondrial fission sites. Elife 4:e11553
Sun, Hua; Al-Romaih, Khaldoun I; MacRae, Calum A et al. (2014) Human Kidney Disease-causing INF2 Mutations Perturb Rho/Dia Signaling in the Glomerulus. EBioMedicine 1:107-15
Korobova, Farida; Gauvin, Timothy J; Higgs, Henry N (2014) A role for myosin II in mammalian mitochondrial fission. Curr Biol 24:409-14
Gurel, Pinar S; Ge, Peng; Grintsevich, Elena E et al. (2014) INF2-mediated severing through actin filament encirclement and disruption. Curr Biol 24:156-64
Hatch, Anna L; Gurel, Pinar S; Higgs, Henry N (2014) Novel roles for actin in mitochondrial fission. J Cell Sci 127:4549-60
Sun, Hua; Schlondorff, Johannes; Higgs, Henry N et al. (2013) Inverted formin 2 regulates actin dynamics by antagonizing Rho/diaphanous-related formin signaling. J Am Soc Nephrol 24:917-29
Korobova, Farida; Ramabhadran, Vinay; Higgs, Henry N (2013) An actin-dependent step in mitochondrial fission mediated by the ER-associated formin INF2. Science 339:464-7
Barua, Moumita; Brown, Elizabeth J; Charoonratana, Victoria T et al. (2013) Mutations in the INF2 gene account for a significant proportion of familial but not sporadic focal and segmental glomerulosclerosis. Kidney Int 83:316-22

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