ABSTRACT
Nutrient-responsive protein kinases control the balance between anabolic growth and catabolic processes such as autophagy. Aberrant regulation of these kinases is a major cause of human disease. We report here that the vertebrate nonreceptor tyrosine kinase Src-related kinase lacking C-terminal regulatory tyrosine and N-terminal myristylation sites (SRMS) inhibits autophagy and promotes growth in a nutrient-responsive manner. Under nutrient-replete conditions, SRMS phosphorylates the PHLPP scaffold FK506-binding protein 51 (FKBP51), disrupts the FKBP51-PHLPP complex, and promotes FKBP51 degradation through the ubiquitin-proteasome pathway. This prevents PHLPP-mediated dephosphorylation of AKT, causing sustained AKT activation that promotes growth and inhibits autophagy. SRMS is amplified and overexpressed in human cancers where it drives unrestrained AKT signaling in a kinase-dependent manner. SRMS kinase inhibition activates autophagy, inhibits cancer growth, and can be accomplished using the FDA-approved tyrosine kinase inhibitor ibrutinib. This illuminates SRMS as a targetable vulnerability in human cancers and as a new target for pharmacological induction of autophagy in vertebrates.
Subject(s)
Autophagy , Neoplasms/metabolism , Neoplasms/pathology , Tacrolimus Binding Proteins/metabolism , src-Family Kinases/metabolism , Adenine/analogs & derivatives , Adenine/pharmacology , Animals , Autophagy/drug effects , Beclin-1/metabolism , Cell Line, Tumor , Cell Proliferation/drug effects , Cellular Senescence/drug effects , Enzyme Activation/drug effects , Mice , Nuclear Proteins/metabolism , Phosphoprotein Phosphatases/metabolism , Phosphorylation/drug effects , Phosphotyrosine/metabolism , Piperidines/pharmacology , Protein Binding/drug effects , Proto-Oncogene Proteins c-akt/metabolism , Signal Transduction/drug effects , src-Family Kinases/antagonists & inhibitorsABSTRACT
BACKGROUND: Epigenetic mechanisms, including DNA methylation, histone modification, and microRNAs, play pivotal roles in stem cell biology. Methyl-CpG binding protein 1 (MBD1), an important epigenetic regulator of adult neurogenesis, controls the proliferation and differentiation of adult neural stem/progenitor cells (aNSCs). We recently demonstrated that MBD1 deficiency in aNSCs leads to altered expression of several noncoding microRNAs (miRNAs). METHODOLOGY/PRINCIPAL FINDINGS: Here we show that one of these miRNAs, miR-195, and MBD1 form a negative feedback loop. While MBD1 directly represses the expression of miR-195 in aNSCs, high levels of miR-195 in turn repress the expression of MBD1. Both gain-of-function and loss-of-function investigations show that alterations of the MBD1-miR-195 feedback loop tip the balance between aNSC proliferation and differentiation. CONCLUSIONS/SIGNIFICANCE: Therefore the regulatory loop formed by MBD1 and miR-195 is an important component of the epigenetic network that controls aNSC fate.