Our studies provide direct evidence that O-glycosylation pathways play a role in the regulation of cell growth through apoptosis and proliferation pathways. A series of small molecular weight analogs of the GalNAc-α-1-O-serine/threonine structure based on 1-benzyl-2-acetamido-2-deoxy-α-O-d-galactopyranoside have been synthesized and tested in the human colorectal cancer cell lines PC/AA/C1/SB10C and HCA7/C29. Three inhibitors, 1-benzyl-2-acetamido-2-deoxy-α-O-d-galactopyranoside, and the corresponding 2-azido- and C-glycoside analogs were screened in these colorectal cancer cell lines at 0.5 mM and showed induction of apoptosis and downregulation of proliferation. Treatment of both cell lines with inhibitors led to changes in glycosylation detected with peanut lectin. The inhibition of glycosyltransferase activity in cell homogenates from human colorectal mucosal cells and cultured cell lines could be shown. The competitive action of the inhibitors resulted in the intracellular formation of 28 aryl-glycan products which were identified by MALDI and electrospray mass spectroscopy. The structures showed a differential pattern for each of the inhibitors in both cell lines. Gene array analysis of the glycogenes illustrated a pattern of glycosyltransferases that matched the glycan structures found in glycoproteins and aryl-glycans formed in the PC/AA/C1/SB10C cells; however, there was no action of the three inhibitors on glycogene transcript levels. The inhibitors act at both intermediary metabolic and genomic levels, resulting in altered protein glycosylation and aryl-glycan formation. These events may play a part in growth arrest.

Semmler L, et al. J Breast Cancer. 2018 Dec;22:e6. https://doi.org/10.4048/jbc.2019.22.e6

Impairment of the complex regulatory network of cell death and survival is frequently the reason for therapy resistance of breast cancer cells and a major cause of tumor progression. We established two independent cell lines from a fast growing mouse breast tumor (WAP-SVT/t transgenic animal). Cells from one line (ME-A cells) are sensitive to apoptotic stimuli such as growth factor depletion or treatment with antitumor agents (e.g. doxorubicin). Cells from the second line (ME-C cells), which carry a missense mutation at the p53 codon 242, are very insensitive to apoptotic stimuli. Co-cultivation experiments revealed that the ME-C cells mediate cell death resistance to the ME-A cells. Microarray and Western blot analysis showed that osteopontin (OPN) is selectively overexpressed by the ME-C cells. This glycoprotein is the most abundant protein secreted by the ME-C cells and we obtained strong indications that OPN is the main antiapoptotic factor. However, the OPN containing ME-C cell medium does not alter the expression level of pro- or antiapoptotic genes or known inhibitors of apoptosis (IAPs). Its signaling involves mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK)1/2 as the kinase inhibitor PD98059 restores apoptosis but not the Akt inhibitor. In the ME-A cells, mitochondrial cytochrome c release occurs with and without external apoptotic stimuli. OPN containing ME-C cell medium does not prevent the mitochondrial cytochrome c release and caspase-9 processing. In serum starved ME-A cells, the OPN containing ME-C cell medium prevents caspase-3 activation. However, in doxorubicin-treated cells, although apoptosis is blocked, it does not inhibit caspase-3. This indicates that the ME-A cells distinguish between the initial apoptotic stimuli and that the cells possess a further uncharacterized control element acting downstream from caspase-3.

B cell chronic lymphocytic leukemia (B-CLL) cannot be cured with conventional chemotherapy. This clinical enigma appears to be at least partially due to the fact that B-CLL cells are resistant to programmed cell death (apoptosis) and that they are arrested in G0/G1 phase of the cell cycle. The reasons for the dysregulation of these two key cellular events in B-CLL are unclear. The present study aimed at determining correlations between the expression levels of proteins regulating apoptosis, cell cycle and DNA repair in B-CLL cells and normal B cells. In addition, the differential sensitivity of B-CLL cells to drug-induced apoptosis was quantified. We show that in B-CLL cells levels of the death-suppressor Bcl-2 correlated positively with those of the pro-apoptotic protein Bax and of the cyclin-dependent kinase (cdk) inhibitor p27^Kip1. In B-CLL cells levels of the anti-apoptotic Bcl-x_L showed a positive correlation with levels of the 80 kDa regulatory component (Ku80) of the DNA-dependent protein kinase that is involved in DNA double-stranded break repair. These correlations were not detected in normal B cells. The sensitivity of leukemic cells to FLUD but not to ADM, CPM or to DEX was reduced in pre-treated patients. These data support the hypothesis that in B-CLL cells death-modulators and molecules modulating cell cycle and DNA repair are regulated in a coordinated manner.

Mutation of the isocitrate-dehydrogenase (IDH) enzymes is one of the central research topics regarding gliomagenesis. Indeed, 70% of gliomas are associated with a gain-of-function IDH mutation and consequently synthesize the oncometabolite, 2-hydroxyglutarate (2-HG). This review aims to...