Regulation of lipid-droplet transport by the perilipin homolog LSD2

Background: Motor-driven transport along microtubules is a primary mechanism for moving and positioning organelles. How such transport is regulated remains poorly understood. For lipid droplets in Drosophila embryos, three distinct phases of transport can be distinguished. To identify factors regulating this transport, we biochemically purified droplets from individual phases and used 2D gel analysis to search for proteins whose amount on droplets changes as motion changes. Results: By mass spectrometry, we identified one such protein as LSD2. Similar to its mammalian counterpart Perilipin, LSD2 is responsible for regulating lipid homeostasis. Using specific antibodies, we confirmed that LSD2 is present on embryonic lipid droplets. We find that lack of LSD2 causes a specific transport defect: Droplet distribution fails to undergo the dramatic changes characteristic of the wild-type. This defect is not due to a complete failure of the core transport machinery - individual droplets still move bidirectionally along microtubules with approximately normal velocities and kinetics. Rather, detailed biophysical analysis suggests that developmental control of droplet motion is lost. We show that LSD2 is multiply phosphorylated in a developmentally controlled manner. LSD2 phosphorylation depends on the transacting signal Halo, and LSD2 can physically interact with the lipid-droplet-associated coordinator Klar, identifying LSD2 as a central player in the mechanisms that control droplet motion. Conclusions: LSD2 appears to represent a new class of regulators, a protein that transduces regulatory signals to a separable core motor machinery. In addition, the demonstration that LSD2 regulates both transport and lipid metabolism suggests a link between lipid-droplet motion and lipid homeostasis.