Actin- and microtubule-dependent regulation of Golgi morphology by FHDC1

The Golgi apparatus is the central hub of intracellular trafficking and consists of tethered stacks of cis, medial, and trans cisternae. In mammalian cells, these cisternae are stitched together as a perinuclear Golgi ribbon, which is required for the establishment of cell polarity and normal subcellular organization. We previously identified FHDC1 (also known as INF1) as a unique microtubule-binding member of the formin family of cytoskeletal-remodeling proteins. We show here that endogenous FHDC1 regulates Golgi ribbon formation and has an apparent preferential association with the Golgi-derived microtubule network. Knockdown of FHDC1 expression results in defective Golgi assembly and suggests a role for FHDC1 in maintenance of the Golgi-derived microtubule network. Similarly, overexpression of FHDC1 induces dispersion of the Golgi ribbon into functional ministacks. This effect is independent of centrosome-derived microtubules and instead likely requires the interaction between the FHDC1 microtubule-binding domain and the Golgi-derived microtubule network. These effects also depend on the interaction between the FHDC1 FH2 domain and the actin cytoskeleton. Thus our results suggest that the coordination of actin and microtubule dynamics by FHDC1 is required for normal Golgi ribbon formation.