Syntaphilin Regulates Mitochondrial Dynamics and Tumor Cell Invasion

Abstract

Recent studies support the concept of spatiotemporal regulation of energy production as a driver of tumor cell motility and invasiveness. However, the molecular mechanisms governing mitochondria repositioning to the leading edge of the tumor cells have remained elusive. In this study, we identify the molecular motors and adaptors responsible for trafficking of mitochondria in tumor cells by a genome‐wide shRNA screen. One of the top hits in the screen was Syntaphilin (SNPH), a molecule that arrests mitochondrial trafficking at sites of high energy demands in neurons. Previously thought to be neuronal specific, SNPH was expressed in brain and non‐neuronal tissues, and in non‐transformed and cancer cell lines. To test the relevance of this pathway, we next silenced SNPH using siRNA or shRNA sequences. Depletion of SNPH constitutively accelerated focal adhesion complex dynamics, stimulated 2D cell motility and increased tumor cell invasion. Furthermore, depletion of SNPH stimulated the repositioning of mitochondria from their perinuclear localization to the cortical cytoskeleton of tumor cells. Reconstitution of SNPH‐depleted cells with siRNA‐insensitive SNPH cDNA reversed the increase in tumor chemotaxis and prevented the increased accumulation of mitochondria to the cortical cytoskeleton. Time lapse imaging revealed that mitochondria in SNPH‐depleted tumor cells exhibited faster speed of movements, higher processivity (time that mitochondria spend in motion/time of analysis), and greater distance traveled, compared to control transfectants. In neurons, SNPH interfaces with microtubule‐mediated trafficking by interacting with kinesin motors and atypical Rho GTPases (Miro) adapters. siRNA silencing of the anterograde kinesin KIF5B or Miro 1 suppressed the increased tumor cell invasion induced by loss of SNPH. In contrast, silencing of Miro2 did not reduce tumor cell invasion in SNPH‐knockdown cells. Next, we expressed various deletion mutants of SNPH that lack the microtubule binding domain (ΔMBD), kinesin‐binding domain (ΔKBD), or LC8‐binding domain (ΔLBD), and looked at their effects on tumor cell invasion. While expression of full length SNPH suppressed tumor cell invasion, ΔMBD, ΔKB, or ΔLBD mutants had no effect. In previous studies, mitochondrial trafficking required energetically active organelles. Here, loss of SNPH was sufficient to deregulate this process, and resulted in robust mitochondrial recruitment to the cortical cytoskeleton in nutrient‐starved tumor cells or oxidative phosphorylation‐deficient ρ0 cells. However, mitochondria from ρ0 cells depleted of SNPH failed to support tumor chemotaxis. In conclusion, we provided compelling evidence that SNPH‐directed mitochondrial dynamics regulates the bioenergetics requirements of tumor cell invasion.Support or Funding InformationThis work was supported by National Institutes of Health (NIH) grants P01 CA140043 (D.C.A.), R01 CA78810 and CA190027 (D.C.A.), F32 CA177018 (M.C.C.), the Office of the Assistant Secretary of Defense for Health Affairs through the Prostate Cancer Research Program under Award No. W81XWH‐13‐1‐0193 (D.C.A.), and a Challenge Award from the Prostate Cancer Foundation (PCF) to M.C.C. and D.C.A.