Sumoylation of KLF4 and SOX2 down-regulates iPS cell induction.
A, Western blotting analysis. HEK293 cell lysates were analyzed 48 h after transduction with lentivirus expressing FLAG-tagged KLF4, SOX2, or OCT4 as indicated. B, quantification of alkaline phosphatase (ALP)-positive colonies 9 days after MEFs were transduced with lentiviruses expressing OCT4, N-MYC (both untagged), and FLAG-tagged (f-) KLF4 and SOX2 proteins as indicated. The p value is shown (n = 3). C, alkaline phosphatase staining of primary iPS colonies 6 or 9 days after infection of MEFs with a mixture of lentiviruses expressing untagged OCT4 and N-MYC, along with lentiviruses for FLAG-tagged KLF4 and SOX2 as indicated. D, alkaline phosphatase staining of primary iPS colonies 6 days after MEFs were infected with the lentivirus expressing FLAG-tagged OCT4 or mutant K123R, along with lentiviruses expressing N-MYC and FLAG-tagged sumoylation-deficient mutants of KLF4 and SOX2. E, quantification of experiments performed as in D.