TP53INP1 (tumor protein 53-induced nuclear protein 1) is a tumor suppressor, whose expression is downregulated in cancers from different organs. It was described as a p53 target gene involved in cell death, cell-cycle arrest and cellular migration. In this work, we show that TP53INP1 is also able to interact with ATG8-family proteins and to induce autophagy-dependent cell death. In agreement with this finding, we observe that TP53INP1, which is mainly nuclear, relocalizes in autophagosomes during autophagy where it is eventually degraded. TP53INP1-LC3 interaction occurs via a functional LC3-interacting region (LIR). Inactivating mutations of this sequence abolish TP53INP1-LC3 interaction, relocalize TP53INP1 in autophagosomes and decrease TP53INP1 ability to trigger cell death. Interestingly, TP53INP1 binds to ATG8-family proteins with higher affinity than p62, suggesting that it could partially displace p62 from autophagosomes, modifying thereby their composition. Moreover, silencing the expression of autophagy related genes (ATG5 or Beclin-1) or inhibiting caspase activity significantly decreases cell death induced by TP53INP1. These data indicate that cell death observed after TP53INP1-LC3 interaction depends on both autophagy and caspase activity. We conclude that TP53INP1 could act as a tumor suppressor by inducing cell death by caspasedependent autophagy. Increased resistance to cell death participates in pancreatic cancer progression. Cells unable to undergo self elimination accumulate mutations and epigenetic modifications that in turn induce uncontrolled replication. 1 Various concomitant mechanisms exist in normal cells to induce death and, as consequence, a number of known cell-death regulators are missing in cancer cells. One of the most studied is the tumor suppressor TP53, which is inactivated in 450% of pancreatic tumors. 2 p53 induces cell death by both direct permeabilization of the outer mitochondrial membrane or translocation to the nucleus where it activates the transcription of several target genes. One of the p53 target genes is TP53INP1 (tumor protein 53-induced nuclear protein 1). 3-6 p53-dependent expression of TP53INP1 is triggered in response to several stress agents such as mutagens, ethanol, heat shock or conditions promoting reactive oxygen species formation (i.e., exposure to UV light or g-irradiation). 4,6 TP53INP1 interacts with kinases, HIPK2 and PKCd, which in turn phosphorylate p53 creating a positive feedback loop between p53 and TP53INP1. 7,8 Our laboratory demonstrated that TP53INP1 is a tumor suppressor on the basis of the following observations: (i) TP53INP1 deficient mice present with an increased susceptibility to tumor development; (ii) TP53INP1 is lost at very early stages of pancreatic carcinogenesis through a mechanism involving the oncogenic miR-155 microRNA and (iii) when TP53INP1 expression is restored in pancreatic cells, it suppresses xenograft growth by increasing apoptotic cell death through a caspase-dependent mechanism. 3,9,10 More recently, in an attempt t...

Thymus-specific serine protease (TSSP) was initially reported as a putative protease specifically expressed in the endosomal compartment of cortical thymic epithelial cells (cTEC). As such, TSSP is potentially involved in the presentation of the self-peptides that are bound to MHC class II molecules expressed at the cTEC surface and are involved in the positive selection of CD4 1 thymocytes. We tested this hypothesis by generating mutant mice deprived of Prss16, the gene encoding TSSP. TSSP-deficient mice produced normal numbers of T cells, despite a decrease in the percentage of cTEC expressing high surface levels of MHC class II. By using sensitive transgenic models expressing MHC class II-restricted TCR transgenes (Marilyn and OT-II), we showed that the absence of TSSP markedly impaired the selection of Marilyn and OT-II CD4 1 T cells. In contrast, selection of CD8 1 T cells expressing an MHC class I-restricted TCR transgene (OT-I) was unaffected. Therefore, TSSP is involved in the positive selection of some CD4 1 T lymphocytes and likely constitutes the first serine protease to play a function in the intrathymic presentation of self-peptides bound to MHC class II complexes.

Toll-like receptors (TLR) are essential components of the innate immune system. Several accessory proteins, such as UNC93B1, are required for transport and activation of nucleic acid sensing Toll-like receptors in endosomes. Here, we show that BAD-LAMP (LAMP5) controls TLR9 trafficking to LAMP1+ late endosomes in human plasmacytoid dendritic cells (pDC), leading to NF-κB activation and TNF production upon DNA detection. An inducible VAMP3+/LAMP2+/LAMP1− endolysosome compartment exists in pDCs from which TLR9 activation triggers type I interferon expression. BAD-LAMP-silencing enhances TLR9 retention in this compartment and consequent downstream signalling events. Conversely, sustained BAD-LAMP expression in pDCs contributes to their lack of type I interferon production after exposure to a TGF-β-positive microenvironment or isolation from human breast tumours. Hence, BAD-LAMP limits interferon expression in pDCs indirectly, by promoting TLR9 sorting to late endosome compartments at steady state and in response to immunomodulatory cues.