tokens: We propose 2 separate PAI - 1 inductory pathways for PMA and IL - 1alpha in HepG2 , both involving protein tyrosine kinase activation ; the serum - induced signaling pathway may ( partially ) overlap with the PMA - activated protein kinase C / mitogen - activated protein kinase kinase pathway , leading to c - Jun homodimer binding to the PAI - 1 TRE .