Systematic Approaches to Study Eclipsed Targeting of Proteins Uncover a New Family of Mitochondrial Proteins.

Dual localization or dual targeting refers to the phenomenon by which identical, or almost identical, proteins are localized to two (or more) separate compartments of the cell. From previous work in the field, we had estimated that a third of the mitochondrial proteome is dual-targeted to extra-mitochondrial locations and suggested that this abundant dual targeting presents an evolutionary advantage. Here, we set out to study how many additional proteins whose main activity is outside mitochondria are also localized, albeit at low levels, to mitochondria (eclipsed). To do this, we employed two complementary approaches utilizing the α-complementation assay in yeast to uncover the extent of such an eclipsed distribution: one systematic and unbiased and the other based on mitochondrial targeting signal (MTS) predictions. Using these approaches, we suggest 280 new eclipsed distributed protein candidates. Interestingly, these proteins are enriched for distinctive properties compared to their exclusively mitochondrial-targeted counterparts. We focus on one unexpected eclipsed protein family of the Triose-phosphate DeHydrogenases (TDH) and prove that, indeed, their eclipsed distribution in mitochondria is important for mitochondrial activity. Our work provides a paradigm of deliberate eclipsed mitochondrial localization, targeting and function, and should expand our understanding of mitochondrial function in health and disease.

Candida albicans evades NK cell elimination via binding of Agglutinin-Like Sequence proteins to the checkpoint receptor TIGIT.

Candida albicans is the most common fungal pathogen and a prevalent cause of deadly bloodstream infections. Better understanding of the immune response against it, and the ways by which it evades immunity, are crucial for developing new therapeutics against it. Natural Killer (NK) cells are innate lymphocytes best known for their role against viruses and tumors. In recent years it became clear that NK cells also play an important role in anti-fungal immunity. Here we show that while NK cells recognize and eliminate C. albicans, the fungal cells inhibit NK cells by manipulating the immune checkpoint receptor TIGIT (T cell immunoreceptor with Ig and ITIM domains) in both humans and mice. We identify the responsible fungal ligands as members of the Als (Agglutinin-Like Sequences) protein family. Furthermore, we show that blocking this interaction using immunotherapy with a TIGIT-blocking antibody can re-establish anti-Candida immunity and serve as a potential therapeutic tool.

Increased chromatin plasticity supports enhanced metastatic potential of mouse melanoma cells.

Metastasis formation is strongly dependent on the migration capabilities of tumor cells. Recently it has become apparent that nuclear structure and morphology affect the cellular ability to migrate. Previously we found that migration of melanoma cells is both associated with and dependent on global chromatin condensation. Therefore, we anticipated that tumor progression would be associated with increased chromatin condensation. Interestingly, the opposite has been reported for melanoma. In trying to resolve this contradiction, we show that during growth conditions, tumor progression is associated with global chromatin de-condensation that is beneficial for faster proliferation. However, upon induction of migration, in both low- and high-metastatic mouse melanoma cells chromatin undergoes condensation to support cell migration. Our results reveal that throughout tumor progression induction of chromatin condensation by migration signals is maintained, whereas the organization of chromatin during growth conditions is altered. Thus, tumor progression is associated with an increase in chromatin dynamics.