Concentrative nucleoside transporter 1 (hCNT1) promotes phenotypic changes relevant to tumor biology in a translocation-independent manner

Abstract

Nucleoside transporters (NTs) mediate the uptake of nucleosides and nucleobases across the plasma membrane, mostly for salvage purposes. The canonical NTs belong to two gene families, SLC29 and SLC28. The former encode equilibrative nucleoside transporter proteins (ENTs), which mediate the facilitative diffusion of natural nucleosides with broad selectivity, whereas the latter encode concentrative nucleoside transporters (CNTs), which are sodium-coupled and show high affinity for substrates with variable selectivity. These proteins are expressed in most cell types, exhibiting apparent functional redundancy. This might indicate that CNTs have specific roles in the physiology of the cell beyond nucleoside salvage. Here, we addressed this possibility using adenoviral vectors to restore tumor cell expression of hCNT1 or a polymorphic variant (hCNT1S546P) lacking nucleoside translocation ability. We found that hCNT1 restoration in pancreatic cancer cells significantly altered cell-cycle progression and phosphorylation status of key signal-transducing kinases, promoted poly-(ADP-ribose) polymerase hyperactivation and cell death and reduced cell migration. Importantly, the translocation-defective transporter triggered these same effects on cell physiology. Moreover, this study also shows that restoration of hCNT1 expression is able to reduce tumor growth in a mouse model of pancreatic adenocarcinoma. These data predict a novel role for a NT protein, hCNT1, which appears to be independent of its role as mediator of nucleoside uptake by cells. Thereby, hCNT1 fits the profile of a transceptor in a substrate translocation-independent manner and is likely to be relevant to tumor biology.

Next-generation sequencing reveals lymph node metastasis associated genetic markers in colorectal cancer

“…Raw data were filtered and adapters were removed. Sequencing results demonstrated that the target sequence was 4.5x10 12 base pairs, with coverage of >99% and the sequencing depth of x250. A quality check was automatically performed on the raw data by the R 3.3.2 rCGH package, and the qualified data were used for subsequent analysis.…”

“…There are multiple chromosome sites with copy number variation (CNV) in CIN-type colorectal cancer (11). If CNV occurs inside or around the tumor-associated gene sequences, oncogenes may be activated and anti-oncogenes may be inactivated, which eventually induces tumorigenesis (12). A previous study indicated that increased CNVs may be associated with the progression of colitis gravis to colorectal cancer (13).…”

Nucleoside transporter proteins as biomarkers of drug responsiveness and drug targets

“…Comprehensive in vitro evidence supports the view that hENT1 activity is a key determinant of gemcitabine action. Overexpression of hENT1 enhances gemcitabine response in human pancreatic cancer, and cells lacking hENT1 expression are highly resistant to gemcitabine ( Mori et al, 2007 ; Perez-Torras et al, 2008 , 2013 ). There is increasing evidence supporting the view that hENT1 is a predictive biomarker for the use of gemcitabine.…”

“…However, the evidence of hCNT1 loss during oncogenesis needs further investigation, because almost all the studies performed so far focused exclusively on hCNT1-related mRNA levels. We have recently demonstrated that restoration of hCNT1 function in pancreatic adenocarcinoma cell lines is able to induce cell cycle arrest, increase cell death by a non-apoptotic mechanism, trigger changes in some intracellular signaling cascades and inhibit cell migration ( Perez-Torras et al, 2013 ). More importantly, all these events can also be induced when expressing a mutated hCNT1 protein that localizes to the plasma membrane but lacks the ability to translocate substrates.…”

Decision letter: Structural basis of nucleoside and nucleoside drug selectivity by concentrative nucleoside transporters

“…These results can also have an impact on basic scientific research. Since some transporter subtypes show significant changes in expression levels between normal and pathological conditions (i.e., cancer), and these changes in transporter expression are usually important for the pathological conditions to persist, a fluorescent compound that is subtype-specific (e.g., pyrrolo-gemcitabine) for a certain transporter family can be a valuable tool to study the role of transporter subtypes in human health and disease through live cell imaging (Farre et al, 2004;Zhang et al, 2006;Bhutia et al, 2011;Perez-Torras et al, 2013). Taken together, this work not only represents an structural study of substrate and drug selectivity by membrane transporters, but our results also provide proof of principle for using this type of structure-function study for modifying drugs so that they are recognized and taken up into the cell by their cognate transporters more efficiently and selectively (Han and Amidon, 2000;Majumdar et al, 2004).…”