Mutant p53 proteins that promote cancer cell invasive growth, metastasis and drug resistance emerge as therapeutic targets. Previously, we reported that suppression of ceramide glycosylation restored wild-type p53 protein and tumor suppressing function in cancer cells heterozygously carrying p53 R273H, a hot-spot missense mutation; however, the mechanisms underlying the control of mutant protein expression remain elusive. Herein, we report that an N 6-methyladenosine

Background: Glucosylceramide synthase catalyzes ceramide glycosylation that regulates the synthesis of glycosphingolipids. Results: Increased globo-series glycosphingolipids in breast cancer stem cells activate c-Src signaling and ␤-catenin-mediated transcription up-regulating stem cell factors. Conclusion: Ceramide glycosylation maintains the stemness of cancer stem cells. Significance: Glycosphingolipids in cell membrane actively participate in maintaining cancer stem cells.

Missense mutation of tumor suppressor p53, which exhibits oncogenic gain-of-function (GOF), not only promotes tumor progression, but also diminishes therapeutic efficacies of cancer treatments. However, it remains unclear how a p53 missense mutant contributes to induced pluripotency of cancer stem cells (CSCs) in tumors exposed to chemotherapeutic agents. More importantly, it may be possible to abrogate the GOF by restoring wild-type p53 activity, thereby overcoming the deleterious effects resulting from heterotetramer formation, which often compromises the efficacies of current approaches being used to reactivate p53 function. Herewith, we report that p53 R273H missense mutant urges cancer cells to spawn CSCs. SW48/TP53 cells, which heterozygously carry the p53 R273H hot-spot mutant (R273H/+, introduced by a CRISPR/Casp9 system), were subchronically exposed to doxorubicin in cell culture and in tumor-bearing mice. We found that p53-R273H (TP53-Dox) cells were drug-resistant and exhibited epithelial-mesenchymal transition (EMT) and increased numbers of CSCs (CD44v6+/CD133+), which resulted in enhanced wound healing and tumor formation. Inhibition of glucosylceramide synthase with d-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) sensitized p53-R273H cancer cells and tumor xenografts to doxorubicin treatments. Intriguingly, PDMP treatments restored wild-type p53 expression in heterozygous R273H mutant cells and in tumors, decreasing CSCs and sensitizing cells and tumors to treatments. This study demonstrated that p53-R273H promotes EMT and induced pluripotency of CSCs in cancer cells exposed to doxorubicin, mainly through Zeb1 and β-catenin transcription factors. Our results further indicate that restoration of p53 through inhibition of ceramide glycosylation might be an effective treatment approach for targeting cancers heterozygously harboring TP53 missense mutations.

(2019) Atezolizumab potentiates Tcell-mediated cytotoxicity and coordinates with FAK to suppress cell invasion and motility in PD-L1 + triple negative breast cancer cells, OncoImmunology, 8:9, e1624128,

No abstract

Mutants of tumor suppressor p53 not only lose the activity in genome stabilizing and in tumor suppression, but also exhibit oncogenic function in cancer cells. Most efforts in restoring p53 biological activity focus on either altering mutant-protein conformation or introducing an exogenous p53 gene into cells to eliminate p53-mutant cancer cells. Being different from these, we report that ceramide can restore the expression of wild-type p53 and induce p53-dependent apoptosis in deletion-mutant cancer cells. We show that endogenous long-carbon chain ceramide species (C16- to C24-ceramides) and exogenous C6-ceramide, rather than other sphingolipids, restore wild-type mRNA (intact exon-5), phosphorylated protein (Ser15 in exon-5) of p53, and p53-responsive proteins, including p21 and Bax, in ovarian cancer cells, which predominantly express a deleted exon-5 of p53 mutant before treatments. Consequently, the restored p53 sensitizes these p53-mutant cancer cells to DNA damage-induced growth arrest and apoptosis. Furthermore, we elucidate that ceramide activates protein phosphatase-1, and then the dephosphorylated serine/arginine-rich splicing-factor 1 (SRSF1) is translocated to the nucleus, thus promoting pre-mRNA splicing preferentially to wild-type p53 expression. These findings disclose an unrecognized mechanism that pre-mRNA splicing dysfunction can result in p53 deletion-mutants. Ceramide through SRSF1 restores wild-type p53 expression versus deletion-mutant and leads cancer cells to apoptosis. This suggests that heterozygous deletion-mutants of p53 can be restored in posttranscriptional level by using epigenetic approaches.

◥Ceramide (Cer) is an active cellular sphingolipid that can induce apoptosis or proliferation-arrest of cancer cells. Nanoparticle-based delivery offers an effective approach for overcoming bioavailability and biopharmaceutics issues attributable to the pronounced hydrophobicity of Cer. Missense mutations of the protein p53, which have been detected in approximately 42% of cancer cases, not only lose the tumor suppression activity of wild-type p53, but also gain oncogenic functions promoting tumor progression and drug resistance. Our previous works showed that cellular Cer can eradicate cancer cells that carry a p53 deletion-mutation by modulating alternative pre-mRNA splicing, restoring wild-type p53 protein expression. Here, we report that new ceramiderubusoside (Cer-RUB) nanomicelles considerably enhance Cer in vivo bioavailability and restore p53-dependent tumor suppression in cancer cells carrying a p53 missense mutation.Natural RUB encapsulated short-chain C 6 -Cer so as to form Cer-RUB nanomicelles ($32 nm in diameter) that substantially enhanced Cer solubility and its levels in tissues and tumors of mice dosed intraperitoneally. Intriguingly, Cer-RUB nanomicelle treatments restored p53-dependent tumor suppression and sensitivity to cisplatin in OVCAR-3 ovarian cancer cells and xenograft tumors carrying p53 R248Q mutation. Moreover, Cer-RUB nanomicelles showed no signs of significant nonspecific toxicity to noncancerous cells or normal tissues, including bone marrow. Furthermore, Cer-RUB nanomicelles restored p53 phosphorylated protein and downstream function to wild-type levels in p53 R172H /þ transgenic mice. Altogether, this study, for the first time, indicates that natural Cer-RUB nanomicelles offer a feasible approach for efficaciously and safely targeting cancers carrying p53 missense mutations.

Glucosylceramide synthase (GCS) is a rate-limiting enzyme catalyzing ceramide glycosylation, thereby regulating cellular ceramide levels and the synthesis of glycosphingolipids (GSLs) in cellular membranes. Alterations of GCS not only affect membrane integrity, but also closely correlate with stem cell pluripotency, cancer drug resistance, GSL storage disorders and other diseases. Enzyme activities measured conventionally with currently available ex-vivo methods do not enable reliable assessment of the roles played by GCS in vivo. We report herein a substrate-incorporation method enabling rapid and efficient assessment of GCS in-vivo activity. Upon nanoparticle-based delivery, fluorescent NBD C6-ceramide was efficiently converted to NBD C6-glucosylceramide in live cells or in mouse tissues, whereupon an HPLC assay enabled detection and quantification of NBD C6-glucosylceramide in the low-femtomolar range. The enzyme kinetics of GCS in live cells and mouse liver were well-described by the Michaelis-Menten model. GCS activities were significantly higher in drug-resistant cancer cells and in tumors overexpressing GCS, but reduced after silencing GCS expression or inhibiting this enzyme. Our studies indicate that this rapid and efficient method provides a valuable means for accurately assessing the roles played by GCS in normal vs. pathological states, including ones involving cancer drug resistance.