GCAF(TMEM251) regulates lysosome biogenesis by activating the mannose-6-phosphate pathway.

The mannose-6-phosphate (M6P) biosynthetic pathway for lysosome biogenesis has been studied for decades and is considered a well-understood topic. However, whether this pathway is regulated remains an open question. In a genome-wide CRISPR/Cas9 knockout screen, we discover TMEM251 as the first regulator of the M6P modification. Deleting TMEM251 causes mistargeting of most lysosomal enzymes due to their loss of M6P modification and accumulation of numerous undigested materials. We further demonstrate that TMEM251 localizes to the Golgi and is required for the cleavage and activity of GNPT, the enzyme that catalyzes M6P modification. In zebrafish, TMEM251 deletion leads to severe developmental defects including heart edema and skeletal dysplasia, which phenocopies Mucolipidosis Type II. Our discovery provides a mechanism for the newly discovered human disease caused by TMEM251 mutations. We name TMEM251 as GNPTAB cleavage and activity factor (GCAF) and its related disease as Mucolipidosis Type V.

Neuroprotective effect of muscone on glutamate-induced apoptosis in PC12 cells via antioxidant and Ca(2+) antagonism.

In the pathogenesis of cerebral ischemia, glutamate excitotoxicity activates N-methyl-d-aspartate (NMDA) receptors which induce calcium influx and oxidative stress. Muscone exerts potent neuroprotective activities on cerebral ischemia. However, its underlying mechanism is yet to be elucidated. In this study, we demonstrated that pretreatment with muscone in PC12 cells markedly ameliorated the loss of cell viability, mitochondrial membrane potential (MMP) collapse, the release of lactate dehydrogenase (LDH), Ca(2+) overload, reactive oxygen species (ROS) generation, and cell apoptosis induced by glutamate. Furthermore, muscone also decreased NR1 (NMDA receptor subunit 1) protein expression, the ratio of Bax/Bcl-2 protein expression and prevented activitation of Ca(2+)/calmodulin-dependent protein kinase type II (CaMKII) and ASK1/JNK/p38 signaling pathways elicited by glutamate in PC12 cells. In conclusion, our results provided novel evidence that muscone protected PC12 cells against glutamate-induced apoptosis by attenuating ROS generation and Ca(2+) influx, via NR1 and CaMKII-depended ASK-1/JNK/p38 signaling pathways.

Discovery of a potent and orally active hedgehog pathway antagonist (IPI-926).

Recent evidence suggests that blocking aberrant hedgehog pathway signaling may be a promising therapeutic strategy for the treatment of several types of cancer. Cyclopamine, a plant Veratrum alkaloid, is a natural product antagonist of the hedgehog pathway. In a previous report, a seven-membered D-ring semisynthetic analogue of cyclopamine, IPI-269609 (2), was shown to have greater acid stability and better aqueous solubility compared to cyclopamine. Further modifications of the A-ring system generated three series of analogues with improved potency and/or solubility. Lead compounds from each series were characterized in vitro and evaluated in vivo for biological activity and pharmacokinetic properties. These studies led to the discovery of IPI-926 (compound 28), a novel semisynthetic cyclopamine analogue with substantially improved pharmaceutical properties and potency and a favorable pharmacokinetic profile relative to cyclopamine and compound 2. As a result, complete tumor regression was observed in a Hh-dependent medulloblastoma allograft model after daily oral administration of 40 mg/kg of compound 28.

Semisynthetic cyclopamine analogues as potent and orally bioavailable hedgehog pathway antagonists.

Herein is reported the synthesis of a novel class of hedgehog antagonists derived from cyclopamine. The acid sensitive D-ring of cyclopamine was homologated utilizing a sequence of chemoselective cyclopropanation and stereoselective acid-catalyzed rearrangement. Further modification of the A/B-ring homoallylic alcohol to the conjugated ketone led to the discovery of new cyclopamine analogues with improved pharmaceutical properties and in vitro potency (EC 50) ranging from 10 to 1000 nM.