MAPK1 and neoplasm: These data conformed with the literature, as PTEN is an important negative regulator of PI3K/AKT signaling, acting as a tumor suppressor [42] Initially, the upregulation of Erk phosphorylation in MCF-7 cells appears surprising, as we previously showed that Sdc-1 depletion reduces Erk activation of serum-starved MCF-7 cells in response to bFGF stimulation.