Microtubule-associated Protein 1 Light Chain Protein 3 Family Post-translational Modification Of The Way

Autophagy almost exists and is highly conservative in all species. It is known that cells display the abnormal response of autophagy in undergoing the stress, apoptosis, cell death and many diseases. Two forms of rat Microtubule-Associated Protein 1 Light Chain 3 (Mapllc3) exist and serve as a subunit of the microtubule-associated protein 1 and an essential constituent of autophagosome membranes, respectively. In vivo, the two functional forms of rat Map1lc3 with apparent mobilities of 18 and 16KB, termed Lc3-I and Lc3-II, separately, were produced by a series of post-translational modifications including a characteristic C-terminal cleavage after the conserved Gly120 residue and this cleavage was essential for the membrane association of the 16KD rat Mapllc3 protein. We found that there are two types of MAP1LC3 in rat, mouse and human,besides that,there is another type(MAP1LC3C) in human. We expressed all MAP1LC3 in HEK293 cells respectively and found that the post translational modification of all MAP1LC3 is similar to yeast Apg8 and rat Map1lc3 identified except human LC3B. Characteristic carboxyl cleavage occurred in conserved glycine of them. However, for human MAP1LC3B, in western blots analysis the overexpression of Myc-tagged human LC3 protein showed only a single 16KD protein band with Anti-Myc epitope monoclonal antibodies. Moreover, it didn't occur the carboxyl cleavage and lysine residual that substitute for the conserved glycine residual is the novel essential site. Subcellular localization by cell fractionation, immunofluorescence revealed that three human isoforms were associated with membranes involved in the autophagic pathway. The glycine and lysine respectively decided the location of autophagosome of human MAP1LC3A and MAP1LC3B. in addition, our results indicated that other proteins were involved in the post tranlational modification of human MAP1LC3B and this modication could be induced by amino acid starvation. These results revealed different regulation of the three human isoforms of MAP1LC3 and implicated that the three isoforms may have different physiological functions.