SPRY4 and neoplasm: Constitutive p38MAPK activation has been shown to cause growth arrest and terminal differentiation in RMS cells.27 We further investigated the role of SPRY4 in inhibiting p38MAPK activation by determining whether p38MAPK deliberately activated by ectopic expression of the constitutive active form of MAPK kinase 6 (MKK6EE) could bypass the inhibitory effect of SPRY4. Increased tumor growth is known to be generally correlated with reduced differentiation.