Page 40 - Read Online

J Cancer Metastasis Treat 2020;6:5 I http://dx.doi.org/10.20517/2394-4722.2020.13 Page 15 of 38
[3]
surprisingly, an enhancer of the Ataxia telangiectasia mutated (ATM) kinase signaling (Palmieri et al. ,
2016). Indeed, the depletion of RANBP9 in NSCLC cells abates ATM activation and its downstream targets
such as p53. Predictably, RANBP9 KO cells are more sensitive than controls to inhibition of the ataxia
and telangiectasia-related kinase, but not ATM. Interestingly, the absence of RANBP9 renders cells more
[1]
sensitive to drugs inhibiting Poly (ADP-ribose)-Polymerase (PARP) (Tessari et al. , 2018).

We present results of our in vitro and in vivo investigation aimed at revealing the mechanisms responsible
for increased sensitivity to specific genotoxic drugs when RANBP9 is absent. For this purpose, we
generated human NSCLC cell lines and new mouse models of NSCLC in which endogenous RANBP9 can
be specifically ablated in cancer cells or, alternatively, tagged with V5-HA for its unequivocal detection.
Tumors of this latter group will enable proteomic studies to identify unknown RANBP9 interactions upon
DNA damaging treatment.

REFERENCES
1. Tessari A, Parbhoo K, Pawlikowski M, Fassan M, Rulli E, et al. RANBP9 affects cancer cells response to genotoxic stress and its
overexpression is associated with worse response to platinum in NSCLC patients. Oncogene 2018;37:6463-76.
2. Matsuoka S, Ballif BA, Smogorzewska A, McDonald ER, 3rd, Hurov KE, et al. ATM and ATR substrate analysis reveals extensive
protein networks responsive to DNA damage. Science 2007; 316:1160-6.
3. Palmieri D, Scarpa M, Tessari A, Uka R, Amari F, et al. Ran Binding Protein 9 (RanBP9) is a novel mediator of cellular DNA damage
response in lung cancer cells. Oncotarget 2016;7:18371-83.

21. One carbon metabolic enzymes play important roles for cancer cells and cancer stem-like
cells

Noriko Gotoh

Cancer Research Institute, Kanazawa University, Ishikawa 920-1192, Japan.

Background and aim: Emerging evidence suggests that cancer stem-like cells (CSCs) are responsible for
[1-6]
drug-resistant tumor recurrence . The one-carbon (1C) metabolism incorporates carbons as building
blocks of purine and pyrimidine that are used for DNA replication and RNA transcription. In the
mitochondria, there are four major enzymes in 1C metabolism. These enzymes are strongly expressed
in cancer cells, while it is scarcely expressed in normal cells. We investigated the role of MTHFD2 and
MTHFD1L among them in cancer cells and CSCs.

Experimental procedure: We depleted expression of MTHFD2 and MTHFD1L in lung cancer cells and
breast cancer cells by using small interfering RNA (siRNAs) or smal hairpin RNA (shRNAs). By using these
cells, we examined cell proliferation and sphere-forming ability in vitro and in vivo. We also examined
expression levels of stemness markers.

Results: We showed that MTHFD2 and MTHFD1L play important roles for cancer cell proliferation, stem-
like properties, and drug resistance. Knockdown of MTHFD2 led to accumulation of 5-aminoimidazole
carboxamide ribonucleotide (AICAR), an intermediate of the purine synthesis pathway, in association with
reduced stem-like properties.

Conclusion: MTHFD2- or MTHFD1L-mediated mitochondrial 1C metabolism appears critical for survival
of CSCs through consumption of AICAR, leading to depletion of the intracellular pool of AICAR. Because
CSCs are dependent on MTHFD2 and MTHFD1L, therapies targeting MTHFD2 may eradicate tumors.