The effect of NAP1L1 on tumor cell proliferation in vitro. In proliferating BON cells, 56% were in the quiescent cell phase (G0/G1) and 44% in the proliferating cell phase (S and G2/M). After two days of serum deprivation, 80% of the cells were quiescent (A). A decrease of NAP1L1 (*p < 0.05) and an increase of p57Kip2 (*p < 0.05) protein expression were evident (B). Inhibiting proliferation by targeting the mTOR pathway (BEZ235) and ERK pathway (GSK1120212) resulted in a similar pattern of expression: NAP1L1 tended to be decreased ((*) p = 0.06) and p57Kip2 was increased (*p < 0.05) while menin did not alter (C). BON cells without NAP1L1 did not grow (*p < 0.0001) and exhibited decreased cell numbers (D). Mean ± SEM.