A proposed pathway for increased expression of the 2 integrin subunit in cells with megakaryocytic features. Both growth factors and PDB indirectly activate the MAPK cascade, including the mitogen-activated protein kinase kinase (MAPKK), extracellular receptor activated kinase (Erk), and Jun kinase via intermediate signaling molecules, including protein kinase C (PKC). Activated Erk and Jun kinase increase c-fos and c-jun synthesis by phosphorylation and activation of transcription factors, including complex factors (TCF), serum response factors (SRF), c-jun, and activating transcription factors (ATF).38 In addition, Erk and Jun kinase phosphorylation augment the activity of both c-fos and c-jun. Newly synthesized (→) and phosphorylated (- - →) c-fos and c-jun family members heterodimerize to bind the tandem and inversely oriented AP1 binding sites of the 2 integrin enhancer and upregulate 2integrin gene expression.
