Abstract
Lipolysis involves a number of components including signaling pathways, droplet-associated proteins, and lipases such as hormone-sensitive lipase (HSL). We used surface enhanced laser desorption/ionization time-of-flight mass spectroscopy to identify cellular proteins that might interact with HSL and potentially influence lipolysis. Using recombinant HSL as bait on protein chips, clusters of proteins of 14.7-18.9, 25.8-26.8, 36.1, 44.3-49.1, and 53.7 kDa were identified that interact with HSL, particularly when lysates were examined from beta-agonist treated mouse adipocytes. The ability to detect these interacting proteins was markedly diminished when the adipocytes were treated with insulin. A very similar pattern of proteins was identified when anti-HSL IgG was used as the bait. Following immunocapture, the identification of the prominent 53.7 kDa protein was carried out by tryptic digestion and MS analysis and determined to be vimentin. The interaction of HSL with vimentin, and its hormonal dependence, was confirmed by coimmunoprecipitation. beta-Agonist stimulated lipolysis and the rate of HSL translocation were impaired in vimentin null adipocytes, even though normal amounts of lipases and droplet-associated proteins are expressed. The current studies provide evidence that vimentin participates in lipolysis through direct, hormonally regulated interactions with HSL.