MAPK1 and neoplasm: As was the case for the inducible nuclear ERK-specific phosphatase DUSP5, increased DUSP6/MKP-3 expression has been observed in primary tumours and cancer cell lines, which harbor mutations in either Ras or Braf, where its role as a negative feedback regulator of ERK activity has led to the suggestion that it may act as a tumour suppressor [125,158,159].