Dual degradation signals destruct GLI1: AMPK inhibits GLI1 through ß-TrCP-mediated proteasome degradation.

Overexpression of the GLI1 gene has frequently been found in various cancer types, particularly in brain tumors, in which aberrant GLI1 induction promotes cancer cell growth. Therefore, identifying the molecular players controlling GLI1 expression is of clinical importance. Previously, we reported that AMPK directly phosphorylated and destabilized GLI1, resulting in the suppression of the Hedgehog signaling pathway. The current study not only demonstrates that AMPK inhibits GLI1 nuclear localization, but further reveals that ß-TrCP plays an essential role in AMPK-induced GLI1 degradation. We found that activation of AMPK promotes the interaction between ß-TrCP and GLI1, and induces ß-TrCP-mediated GLI1-ubiquitination and degradation. Inhibiting AMPK activity results in the dissociation of the ß-TrCP and GLI1 interaction, and diminishes ß-TrCP-mediated-GLI1 ubiquitination and degradation. On GLI1, substitution of AMPK phosphorylation sites to aspartic acid (GLI13E) results in stronger binding affinity of GLI1 with ß-TrCP, accompanied by enhanced GLI1 ubiquitination and later degradation. In contrast, the GLI1 alanine mutant (GLI13A) shows weaker binding with ß-TrCP, which is accompanied by reduced ß-TrCP-mediated ubiquitination and degradation. Together, these results demonstrate that AMPK regulates GLI1 interaction with ß-TrCP by phosphorylating GLI1 and thus both post-translational modifications by AMPK and ß-TrCP ultimately impact GLI1 degradation.

Targeting the Hedgehog Pathway in Pediatric Medulloblastoma.

Medulloblastoma (MB), a primitive neuroectomal tumor of the cerebellum, is the most common malignant pediatric brain tumor. The cause of MB is largely unknown, but aberrant activation of Hedgehog (Hh) pathway is responsible for ~30% of MB. Despite aggressive treatment with surgical resection, radiation and chemotherapy, 70%-80% of pediatric medulloblastoma cases can be controlled, but most treated patients suffer devastating side effects. Therefore, developing a new effective treatment strategy is urgently needed. Hh signaling controls transcription of target genes by regulating activities of the three Glioma-associated oncogene (Gli1-3) transcription factors. In this review, we will focus on current clinical treatment options of MB and discuss mechanisms of drug resistance. In addition, we will describe current known molecular pathways which crosstalk with the Hedgehog pathway both in the context of medulloblastoma and non-medulloblastoma cancer development. Finally, we will introduce post-translational modifications that modulate Gli1 activity and summarize the positive and negative regulations of the Hh/Gli1 pathway. Towards developing novel combination therapies for medulloblastoma treatment, current information on interacting pathways and direct regulation of Hh signaling should prove critical.

Algoriphagus machipongonensis sp. nov., co-isolated with a colonial choanoflagellate.

A Gram-negative, non-motile, non-spore-forming bacterial strain, PR1(T), was isolated from a mud core sample containing colonial choanoflagellates near Hog Island, Virginia, USA. Strain PR1(T) grew optimally at 30 °C and with 3 % (w/v) NaCl. Strain PR1(T) contained MK-7 as the major menaquinone as well as carotenoids but lacked pigments of the flexirubin-type. The predominant fatty acids were iso-C(15 : 0) (29.4 %), iso-C(17 : 1)ω9c (18.5 %) and summed feature 3 (C(16 : 1)ω6c and/or C(16 : 1)ω7c; 11.3 %). The major polar lipids detected in strain PR1(T) were phosphatidylethanolamine, an unknown phospholipid, an aminophospholipid, an aminolipid and two lipids of unknown character. The DNA G+C content was 38.7 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain PR1(T) fell within the cluster comprising the genus Algoriphagus and was most closely related to Algoriphagus halophilus JC 2051(T) (95.4 % sequence similarity) and Algoriphagus lutimaris S1-3(T) (95.3 % sequence similarity). The 16S rRNA gene sequence similarity between strain PR1(T) and the type strains of other species of the genus Algoriphagus were in the range 91-95 %. Differential phenotypic properties and phylogenetic and genetic distinctiveness of strain PR1(T) demonstrated that this strain was distinct from other members of the genus Algoriphagus, including its closest relative, A. halophilus. Based on phenotypic, chemotaxonomic, phylogenetic and genomic data, strain PR1(T) should be placed in the genus Algoriphagus as a representative of a novel species, for which the name Algoriphagus machipongonensis sp. nov. is proposed. The type strain is PR1(T) (= ATCC BAA-2233(T) = DSM 24695(T)).