A transcriptional variant of the LC3A gene is involved in autophagy and frequently inactivated in human cancers

Microtubule-associated protein 1 light chain 3 has an important role in autophagy. The human LC3 gene family has five members, LC3A (variant-1: v1 and -2: v2), LC3B, LC3B2 and LC3C. Although a form of LC3B modified by phosphatidylethanolamine (form-II) is localized in autophagosomes, it is not clear whether other LC3 proteins also function in autophagy. Here, we examined the association between autophagy and human LC3 proteins during starvation- or p53-induced autophagy in Saos-2 cells. In an analysis of the intracellular distribution of each LC3 protein fused with GFP, GFP-LC3Av1 was frequently localized in autophagosomes with a punctate pattern, similar to GFP-LC3B. Further, endogenous LC3Av1 generated form-II and mostly localized in LC3B-positive autophagosomes during the induced autophagy. Interestingly, LC3Av1, not LC3B, was frequently inactivated at the transcriptional level in various human cancer cell lines (111/244 cell lines, 45.5%) and its inactivation was due to aberrant DNA methylation in esophageal squamous cell carcinoma (ESCC) cell lines and primary tumors. Restoration of LC3Av1 expression in KYSE170 cells, an LC3Av1-inactivated ESCC cell line, showed the inhibition of tumor growth in vivo. These results suggest that LC3Av1, not only LC3B, functions in autophagy and further, LC3Av1 may be crucial in carcinogenesis. Oncogene (2012) 31, 4397-4408; doi: 10.1038/onc.2011.613; published online 16 January 2012