The Kinesin II Family Motor Protein, KIF17, contributes to Microtubule Stabilization and Actin Polymerization in Epithelial Cells

Kinesin family motor proteins are microtubule (MT)-stimulated ATPases that play integral roles in intracellular transport along the MT cytoskeleton and in organizing the mitotic spindle. Several kinesins, including KIF17, are also known to regulate MT dynamics and organization. The lab also found that expression of a truncated version of KIF17 encoding only the MT-binding, motor domain fused to mCherry (mCh-KIF17M^1-339), induces MT stabilization in epithelial cells. Interestingly, mCh-KIF17M^1-339 colocalizes with actin, not MTs, at the cell cortex and stimulates polymerization/accumulation of actin-GFP. We constructed and expressed 2 longer versions of the KIF17 N-terminal domain in MDCK epithelial cells: (i) KIF17M^1-369, which includes the neck-linker region needed for dimerization and (ii) KIF17M^1-490, including the neck-linker and first coiled-coil domain. We then tested if these dimeric KIF17 constructs also affect actin polymerization and MT stabilization. In functional assays, we find that overexpressed KIF17M^1-369 localizes at the cortex and stimulates cortical polymerization of actin-GFP and induces MT stabilization. Expression of KIF17M^1-490 also induces MT stabilization but does not stimulate polymerization of cortical actin-GFP. These data demonstrate that the first coiled-coil domain influences the localization and function of KIF17. Together, our findings reveal a novel role for KIF17 on actin and suggest that different regions of the KIF17 holoenzyme affect its functions on MTs and actin in cells. We observed no significant effect of KIF17M^1-369 (or of KIF17M^1-339) on actin visualized with fluorescent LifeAct, our data suggest that KIF17M stimulates polymerization of branched actin but not unbranched actin filaments.