RUMI is a novel negative prognostic marker and therapeutic target in non–small‐cell lung cancer

Abstract

Recent comprehensive next-generation genome and transcriptome analyses in lung cancer patients, several clinical observations, and compelling evidence from mouse models of lung cancer have uncovered a critical role for Notch signaling in the initiation and progression of non-small-cell lung cancer (NSCLC). Notably, Rumi is a "protein O-glucosyltransferase" that regulates Notch signaling through O-glucosylation of Notch receptors, and is the only enzymatic regulator whose activity is required for both ligand-dependent and ligand-independent activation of Notch. We have conducted a detailed study on RUMI's involvement in NSCLC development and progression, and have further explored the therapeutic potential of its targeting in NSCLC. We have determined that Rumi is highly expressed in the alveolar and bronchiolar epithelia, including club cells and alveolar type II cells. Remarkably, RUMI maps to the region of chromosome 3q that corresponds to the major signature of neoplastic transformation in NSCLC, and is markedly amplified and overexpressed in NSCLC tumors. Notably, RUMI expression levels are predictive of poor prognosis and survival in NSCLC patients. Our data indicates that RUMI modulates Notch activity in NSCLC cells, and that its silencing dramatically decreases cell proliferation, migration, and survival. RUMI downregulation causes severe cell cycle S-phase arrest, increases genome instability, and induces late apoptotic-nonapoptotic cell death. Our studies demonstrate that RUMI is a novel negative prognostic factor with significant therapeutic potential in NSCLC, which embodies particular relevance especially when considering that, while current Notch inhibitory strategies target only ligand-dependent Notch activation, a large number of NSCLCs are driven by ligand-independent Notch activity.

Xylosyl Extension of O-Glucose Glycans on the Extracellular Domain of NOTCH1 and NOTCH2 Regulates Notch Cell Surface Trafficking

“…In this study, we only showed that the xylosyl extension of O-Glc glycans may be involved in the regulation of Notch receptor trafficking using an overexpression system with room for improvement, and it should be further investigated how a xylosyl extension is involved in the above-mentioned, and possibly other, biological processes in vivo. Taken together, our findings suggest the importance of protein folding and O-glucosylation on multiple cysteine-rich EGF repeats of Notch receptors and provide insights into the pathological mechanisms in POGLUT1-related human diseases [51,52,[55][56][57].…”

Notch Transduction in Non-Small Cell Lung Cancer

“…Along, these observations would seem to suggest that Lkb1 loss, via activation of the ID1 pathway, would interact with Notch in NSCLC tumors and, therefore, would render Notch activity functionally relevant in the development and progression of tumors of this subtype. In line to these findings, nonetheless, is the observation that Notch action inhibition in H1299 and A549 Kras mutant cells with γ-secretase inhibitor DAPT, alone or in combination with gemcitabine, had a marked effect in NSCLC cell viability and colony-forming potential [123], and that Rumi knockdown, globally inactivating Notch signaling in NSCLC A549 and H23 cells (both Lkb1-deficient [118,124]) results in marked anti-oncogenic exertion, including a significant reduction in cell proliferation, migration and survival [100]. These concurrent findings, therefore, would positively suggest that in the context of Lkb1 deficiency Notch is also in fact promoting tumor growth and neoplastic progression, and that it is possible that ID1 may be a cooperative factor likely releasing the otherwise oscillatory negative autoregulation of Hes1, and, therefore, further indicating that the molecular interaction between these two pathways is, in this case, indispensable.…”

“…In this respect, it is important to mention that pharmacological or genetic inactivation of Notch alone has been shown to have an epistatic effect to both Kras G12D and Kras G12V mutations [87,88]. Furthermore, genetic silencing of Rumi, which regulates both ligand-dependent and -independent Notch activity [155,156], caused marked cell proliferation decrease and cell cycle S-phase arrest in both Kras G12S A549 cells and Kras G12C H23 cells [100].…”

“…Notch2 alterations in NSCLC, on the other hand, have been reported to include both activating and inactivating mutations, and, in contrast to what has been observed in Notch1 , these alterations are mainly found to be gene amplifications (TCGA, MSKCC, cBioportal ( [ 98 , 99 ])), both in ACL and SCC, which could in fact go along with the increased expression observed in patients with advanced NSCLC stage and disease relapse [ 16 ]. Notably, Rumi ( Poglut1 ) amplification has also been observed in NSCLC patients, and the protein levels of this Notch regulator in NSCLC tumors are directly associated with poor prognosis and decreased patient survival [ 100 ]. Although the specific effects of the distinct Notch2 point mutations have not been functionally experimentally tested yet, this is a subject that reclaims further exploration to discern Notch2 functional action in NSCLC.…”

The role of developmental signaling pathways in non-small cell lung carcinoma

“…Diminished stemness markers, reduced resistance miR-223 [90] Upregulated; leads to overactivation of Notch Reduced CD44+ subpopulation of CSCs, improved response to erlotinib Rumi, protein-O-glucosyltransferase [91] Two to three-fold higher expression in NSCLC Knockdown led to decreased Hes1, Hey1, cell proliferation and migration induced EMT by binding to miR-137 and thus reversed the effects of Notch downregulation [83]. Several other novel pathway mediators along with their role in Notch pathway signaling and the results of their pharmacological targeting are presented in Table 2.…”