Molecular phenotyping of colorectal neoplasia shows dynamic and adaptive cancer stem cell population admixture

Intestinal homeostasis is underpinned by LGR5+ve crypt-base columnar stem cells (CBCs), but following injury, dedifferentiation results in the emergence of LGR5-ve regenerative stem cell populations (RSCs), characterised by fetal transcriptional profiles. Neoplasia hijacks regenerative signalling, so we assessed the distribution of CBCs and RSCs in mouse and human intestinal tumors. Using combined molecular-morphological analysis we demonstrate variable expression of stem cell markers across a range of lesions. The degree of CBC-RSC admixture was associated with both epithelial mutation and microenvironmental signalling disruption, and could be mapped across disease molecular subtypes. The CBC-RSC equilibrium was adaptive, with a dynamic response to acute selective pressure, and adaptability was associated with chemoresistance. We propose a fitness landscape model where individual tumors have equilibrated stem cell population distributions along a CBC-RSC phenotypic axis. Cellular plasticity is represented by position shift along this axis, and is influenced by cell-intrinsic, extrinsic and therapeutic selective pressures

Leptin-dependent Phosphorylation of PTEN Mediates Actin Restructuring and Activation of ATP-sensitive K+ Channels

Leptin activates multiple signaling pathways in cells, including the phosphatidylinositol 3-kinase pathway, indicating a degree of cross-talk with insulin signaling. The exact mechanisms by which leptin alters this signaling pathway and how it relates to functional outputs are unclear at present. A previous study has established that leptin inhibits the activity of the phosphatase PTEN (phosphatase and tensin homolog deleted on chromosome 10), an important tumor suppressor and modifier of phosphoinositide signaling. In this study we demonstrate that leptin phosphorylates multiple sites on the C-terminal tail of PTEN in hypothalamic and pancreatic β-cells, an action not replicated by insulin. Inhibitors of the protein kinases CK2 and glycogen synthase kinase 3 (GSK3) block leptin-mediated PTEN phosphorylation. PTEN phosphorylation mutants reveal the critical role these sites play in transmission of the leptin signal to F-actin depolymerization. CK2 and GSK3 inhibitors also prevent leptin-mediated F-actin depolymerization and consequent ATP-sensitive K+ channel opening. GSK3 kinase activity is inhibited by insulin but not leptin in hypothalamic cells. Both hormones increase N-terminal GSK3 serine phosphorylation, but in hypothalamic cells this action of leptin is transient. Leptin, not insulin, increases GSK3 tyrosine phosphorylation in both cell types. These results demonstrate a significant role for PTEN in leptin signal transmission and identify GSK3 as a potential important signaling node contributing to divergent outputs for these hormones