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The Ser/Thr protein kinase MTOR (mechanistic target of rapamycin kinase) regulates cellular metabolism and controls macroautophagy/autophagy. Autophagy has both metabolic and quality control functions, including recycling nutrients at times of starvation and removing dysfunctional intracellular organelles. Lysosomal damage is one of the strongest inducers of autophagy, and yet mechanisms of its activation in response to lysosomal membrane damage are not fully understood. Our recent study has uncovered a new signal transduction system based on cytosolic galectins that elicits autophagy by controlling master regulators of metabolism and autophagy, MTOR and AMPK, in response to lysosomal damage. Thus, intracellular galectins are not, as previously thought, passive tags recognizing damage to guide selective autophagy receptors, but control the activation state of AMPK and MTOR in response to endomembrane damage. Abbreviations: MTOR: mechanistic target of rapamycin kinase; AMPK: AMP-activated protein kinase / Protein Kinase AMP-Activated; SLC38A9: Solute Carrier Family 38 Member 9; APEX2: engineered ascorbate peroxidase 2; RRAGA/B: Ras Related GTP Binding A or B; LAMTOR1: Late Endosomal/Lysosomal Adaptor, MAPK and MTOR Activator 1; LGALS8: Lectin, Galactoside-Binding, Soluble, 8 / Galectin 8; LGALS9: Lectin, Galactoside-Binding, Soluble, 9 / Galectin 9; TAK1: TGF-Beta Activated Kinase 1 / Mitogen-Activated Protein Kinase Kinase Kinase 7 (MAP3K7); STK11/LKB1: Serine/Threonine Kinase 11 / Liver Kinase B1; ULK1: Unc-51 Like Autophagy Activating Kinase 1.

Intestinal epithelial cells (IEC) drive regulatory T cell (Treg) responses by promoting the differentiation of aldehyde dehydrogenase (ALDH)-expressing CD103+ dendritic cells (DC). Apical stimulation of TLR9 by CpG DNA on IEC supports galectin-9 expression by IEC, which is promoted by short-chain galacto-oligosaccharides and long-chain fructo-oligosaccharides (GF). While galectin-9 can induce the maturation of monocyte-derived DC (moDC), the contribution of galectin-9 on the induction of ALDH activity in DC is not known. To this end, DC were stimulated with galectin-9, and ALDH activity and the expression of CD103 were assessed. ALDH activity was increased by moDC exposed to galectin-9, while the expression of CD103 remained unaltered. Galectin-9 secreted by IEC apically exposed to CpG DNA and GF enhanced ALDH activity, but not CD103 expression by moDC, which was abrogated upon galectin-9 neutralization. Similar observations were found in murine GM-CSF-cultured bone marrow-derived DC (BMDC). Using Flt3L-cultured BMDC and ex vivo murine splenic DC, it was observed that galectin-9 only enhanced ALDH activity in the presence of GM-CSF in CD103- cells. The induction of ALDH activity in BMDC was dependent on p38 and PI3K signaling. These data indicate a novel role for galectin-9 in modulating innate immunity by inducing ALDH activity in DC.

The ability to evade the immune system is crucial for cancer cells to survive. In pancreatic ductal adenocarcinoma (PDAC), various mechanisms contributing to immunosuppression have been described, including the recruitment of suppressive immune cells like M2 macrophages, the expression of cell membrane attached proteins like PDL-1, or secretion of extracellular proteins inducing immune cell apoptosis. PDAC is characterized by a rich stroma, consisting of large quantities of extracellular matrix (ECM) proteins, immune cells, fibroblasts and blood vessels. Cancer cell-derived proteins deposited in the stroma can inhibit immune cell function and thereby contribute to the progression of the disease. Galectin 4 (gal 4) is highly expressed by PDAC cancer cells and is secreted into the stroma and has recently been shown to have the capacity to induce T-cell apoptosis in PDAC tumor. High levels of gal 4 is also associated to poor prognosis and reduced immune activity in PDAC patients. Here we show that sets of immunosuppressive genes form groups based on correlation of expression levels. Gal 4 gene expression correlates with other galectin family proteins, collectively clustering into a distinct immune evasion group. This cluster has negative correlation to other more classical immunosuppressive factors, such as PDL-1, CXCL12, and TGFBI, indicating that a subset of tumors mainly relies on galectins to achieve immune evasion. Conversely, tumors with low expression of gal 4 have high expression of one or more of the classical immunosuppressive factors. These results indicate that different tumors rely on different mechanisms to achieve immune evasion and emphasize the need for personalized treatment strategies when targeting immunosuppression in PDAC.