hMan2c1 transgene promotes tumor progress in mice

α-1,2-Mannosidase MAN1C1 Inhibits Proliferation and Invasion of Clear Cell Renal Cell Carcinoma

Background: This study investigated the biological function of the gene MAN1C1 α-mannosidase in renal cell carcinoma. It has been reported that MAN1C1 is probably a potential tumor suppressor gene in Wilms. However, the role of MAN1C1 in human clear cell renal cell carcinoma (ccRCC) has not been reported.

Methods: In this study, MAN1C1 gene over-expression was used to transfect human renal cancer cell lines 786-O and OS-RC-2 to study apoptosis and the underlying mechanisms which influence epithelial-mesenchymal transition.

Results: MAN1C1 was down-regulated in ccRCC and related to the clinicopathological factors and prognosis of ccRCC. We revealed that over-expression MAN1C1 showed anti-tumor effect by inducing apoptosis, as determined by Cell Counting Kit-8 (CCK-8) assay, cell cycle analysis, and western blot analysis. What's more, MAN1C1 over-expression remarkably increased the ratio of Bax/Bcl-2 and inhibited epithelial-mesenchymal transition by increasing the expression of E-CA. In addition, the ratio of Bax/Bcl-2 and E-CA were also increased in MAN1C1 gene over-expression renal cancer cells compared with the control cells.

Conclusion: We find that re-expression of silenced MAN1C1 in ccRCC cell lines inhibited cell viability, colony formation, induced apoptosis, suppressed cell invasion and migration. In conclusion, MAN1C1 is a novel functional tumor suppressor in renal carcinogenesis. This is the first time that the function of MAN1C1 gene has been verified in the renal tumor tissue so far.

Ancient Haplotypes at the 15q24.2 Microdeletion Region Are Linked to Brain Expression of MAN2C1 and Children's Intelligence

The chromosome bands 15q24.1-15q24.3 contain a complex region with numerous segmental duplications that predispose to regional microduplications and microdeletions, both of which have been linked to intellectual disability, speech delay and autistic features. The region may also harbour common inversion polymorphisms whose functional and phenotypic manifestations are unknown. Using single nucleotide polymorphism (SNP) data, we detected four large contiguous haplotype-genotypes at 15q24 with Mendelian inheritance in 2,562 trios, African origin, high population stratification and reduced recombination rates. Although the haplotype-genotypes have been most likely generated by decreased or absent recombination among them, we could not confirm that they were the product of inversion polymorphisms in the region. One of the blocks was composed of three haplotype-genotypes (N1a, N1b and N2), which significantly correlated with intelligence quotient (IQ) in 2,735 children of European ancestry from three independent population cohorts. Homozygosity for N2 was associated with lower verbal IQ (2.4-point loss, p-value = 0.01), while homozygosity for N1b was associated with 3.2-point loss in non-verbal IQ (p-value = 0.0006). The three alleles strongly correlated with expression levels of MAN2C1 and SNUPN in blood and brain. Homozygosity for N2 correlated with over-expression of MAN2C1 over many brain areas but the occipital cortex where N1b homozygous highly under-expressed. Our population-based analyses suggest that MAN2C1 may contribute to the verbal difficulties observed in microduplications and to the intellectual disability of microdeletion syndromes, whose characteristic dosage increment and removal may affect different brain areas.

Generation and degradation of free asparagine-linked glycans

Asparagine (N)-linked protein glycosylation, which takes place in the eukaryotic endoplasmic reticulum (ER), is important for protein folding, quality control and the intracellular trafficking of secretory and membrane proteins. It is known that, during N-glycosylation, considerable amounts of lipid-linked oligosaccharides (LLOs), the glycan donor substrates for N-glycosylation, are hydrolyzed to form free N-glycans (FNGs) by unidentified mechanisms. FNGs are also generated in the cytosol by the enzymatic deglycosylation of misfolded glycoproteins during ER-associated degradation. FNGs derived from LLOs and misfolded glycoproteins are eventually merged into one pool in the cytosol and the various glycan structures are processed to a near homogenous glycoform. This article summarizes the current state of our knowledge concerning the formation and catabolism of FNGs.

PTEN function: the long and the short of it

Phosphatase and tensin homolog deleted on chromosome ten (PTEN) is a phosphatase that is frequently altered in cancer. PTEN has phosphatase-dependent and -independent roles, and genetic alterations in PTEN lead to deregulation of protein synthesis, the cell cycle, migration, growth, DNA repair, and survival signaling. PTEN localization, stability, conformation, and phosphatase activity are controlled by an array of protein-protein interactions and post-translational modifications. Thus, PTEN-interacting and -modifying proteins have profound effects on the tumor suppressive functions of PTEN. Moreover, recent studies identified mechanisms by which PTEN can exit cells, via either exosomal export or secretion, and act on neighboring cells. This review focuses on modes of PTEN protein regulation and ways in which perturbations in this regulation may lead to disease.

Accumulation of free oligosaccharides and tissue damage in cytosolic α-mannosidase (Man2c1)-deficient mice

Free Man(7-9)GlcNAc2 is released during the biosynthesis pathway of N-linked glycans or from misfolded glycoproteins during the endoplasmic reticulum-associated degradation process and are reduced to Man5GlcNAc in the cytosol. In this form, free oligosaccharides can be transferred into the lysosomes to be degraded completely. α-Mannosidase (MAN2C1) is the enzyme responsible for the partial demannosylation occurring in the cytosol. It has been demonstrated that the inhibition of MAN2C1 expression induces accumulation of Man(8-9)GlcNAc oligosaccharides and apoptosis in vitro. We investigated the consequences caused by the lack of cytosolic α-mannosidase activity in vivo by the generation of Man2c1-deficient mice. Increased amounts of Man(8-9)GlcNAc oligosaccharides were recognized in all analyzed KO tissues. Histological analysis of the CNS revealed neuronal and glial degeneration with formation of multiple vacuoles in deep neocortical layers and major telencephalic white matter tracts. Enterocytes of the small intestine accumulate mannose-containing saccharides and glycogen particles in their apical cytoplasm as well as large clear vacuoles in retronuclear position. Liver tissue is characterized by groups of hepatocytes with increased content of mannosyl compounds and glycogen, some of them undergoing degeneration by hydropic swelling. In addition, lectin screening showed the presence of mannose-containing saccharides in the epithelium of proximal kidney tubules, whereas scattered glomeruli appeared collapsed or featured signs of fibrosis along Bowman's capsule. Except for a moderate enrichment of mannosyl compounds and glycogen, heterozygous mice were normal, arguing against possible toxic effects of truncated Man2c1. These findings confirm the key role played by Man2c1 in the catabolism of free oligosaccharides.

Dual functions for cytosolic α-mannosidase (Man2C1): its down-regulation causes mitochondria-dependent apoptosis independently of its α-mannosidase activity

Cytosolic α-mannosidase (Man2C1) trims free oligosaccharides in mammalian cells, and its down-regulation reportedly delays cancer growth by inducing mitotic arrest or apoptosis. However, the mechanism by which Man2C1 down-regulation induces apoptosis is unknown. Here, we demonstrated that silencing of Man2C1 via small hairpin RNAs induced mitochondria-dependent apoptosis in HeLa cells. Expression of CHOP (C/EBP homologous protein), a transcription factor critical to endoplasmic reticulum stress-induced apoptosis, was significantly up-regulated in Man2C1 knockdown cells. However, this enhanced CHOP expression was not caused by endoplasmic reticulum stress. Interestingly, Man2C1 catalytic activity was not required for this regulation of apoptosis; introduction of mutant, enzymatically inactive Man2C1 rescued apoptotic phenotypes of Man2C1 knockdown cells. These results show that Man2C1 has dual functions: one in glycan catabolism and another in apoptotic signaling.

α-Mannosidase 2C1 attenuates PTEN function in prostate cancer cells

PTEN dephosphorylates the 3-position phosphate of phosphatidylinositol 3,4,5 triphosphate (PIP(3)), thereby inhibiting AKT activation. Although attenuation of PTEN function has a major role in tumourigenesis, the underlying mechanisms remain unclear. Here we show that α-mannosidase 2C1 (MAN2C1) inhibits PTEN function in prostate cancer (PC) cells and is associated with a reduction in PTEN function in primary PC. MAN2C1 activates AKT and promotes the formation of PTEN-positive DU145 cell-derived xenograft tumours by imparing endogenous PTEN function. In 659 PC patients who were examined, ~60% of tumours were PTEN positive with elevated AKT activation. Of these, 80% display MAN2C1 overexpression that co-localizes with PTEN. Increases in MAN2C1 were detected only in PTEN-positive prostatic intraepithelial neoplasia and carcinomas, and showed a significant association with PC recurrence only in patients with PTEN-positive PCs. Mechanistically, MAN2C1 binds PTEN thereby inhibiting its PIP(3) phosphatase activity. These findings show that MAN2C1 function as a PTEN-negative regulator in PC cells.