SIMPLE/LITAF Expression Induces the Translocation of the Ubiquitin Ligase Itch towards the Lysosomal Compartments

Abstract

LITAF is a small cellular protein with an unknown function. The C-terminus of LITAF contains a highly conserved domain termed the SIMPLE-like domain (SLD), while the N-terminus contains two PPXY motifs that mediate protein-protein interactions with WW-domain containing proteins. LITAF also harbors two endosome/lysosome targeting sequences at its C-terminus, but there has been conflicting reports regarding its intracellular localization. Here, we demonstrate that LITAF is localized to the late endosome/lysosomal compartment in a variety of cell lines. We also show that Itch, a WW-domain containing protein, and LITAF strongly interact and that this interaction depends on the two PPXY motifs in the N-terminus of LITAF. Interestingly, co-expression of LITAF with Itch induces major changes in Itch intracellular localization, bringing Itch from the trans-Golgi network to lysosomes. We show that this re-localization is dependent upon the interaction with the PPXY sequences of LITAF, since disruption of these binding motifs completely abrogates Itch re-localization.

Dysregulated Inflammatory Signaling upon Charcot-Marie-Tooth Type 1C Mutation of SIMPLE Protein

“…PPXY motifs are also found in all of the ␣-arrestin proteins except the Arrdc5 member (79,80). Third, SIMPLE encodes a PTAP motif for its interaction with ESCRT-1 protein Tsg101 (34,37). Interaction with Tsg101 is unique for Arrdc1 among the six members of the ␣-arrestin family (81).…”

“…4A). Indeed, previous reports demonstrated that the PTAP and PPXY motifs are required for the interaction of SIMPLE with Tsg101 and Nedd4 E3 ligase, respectively (34,37).…”

“…Some of these ubiquitin ligases, such as Nedd4 and Itch, are known SIMPLE interacting proteins (Fig. 4A) (34,37). Lastly, SIMPLE is also known as LITAF, which is induced upon inflammation and modulates cytokine gene induction (54)(55)(56).…”

Autosomal dominant demyelinating Charcot–Marie–Tooth (CMT1) neuropathies

“…CMT1C is linked to the chromosome 16p13.1 and mutations in LITAF (lipopolysaccharide-induced TNF factor), also known as SIMPLE (small integral membrane protein of lysosome/late endosome) or PIG-7 (p53 inductible gene-7) gene [46]. Initially, two transcripts, encoding different proteins (LITAF and SIMPLE), were reported [2].…”

Cellular LITAF Interacts with Frog Virus 3 75L Protein and Alters Its Subcellular Localization

“…LITAF is predicted to encode a 161-amino-acid protein with distinct N and C termini (6). The N terminus of LITAF contains proline-rich binding domains for several cellular proteins, including neural precursor cell expressed, developmentally downregulate 4 (Nedd4) (3,7), tumor susceptibility gene 101 (TSG101) (8), and Itch (9), which function along a conserved pathway of lysosomal protein degradation. The C terminus of LITAF contains an arrangement of cysteine residues resembling a RING finger domain (4).…”