DNMT1 and central nervous system cancer: The disruption of the Dnmt1/PCNA interactions is also confirmed by the use of a proximity ligation in situ assay (P-LISA) and the significant reduction of the Dnmt1/PCNA interactions in U251 cells (a glioma cell line) compared with Astro#40 cells (a non-tumor glial cell lines) (p = 0.003) (Figure 2B).