Figure 9 - Protein kinase C (PKC)-mediated contraction of LES circular muscle.

PKC-mediated contraction may depend on activation of at least two pathways: an ERK1/ERK2 MAP kinase pathway linked to the Ca-independent integrin-linked kinase (ILK), and a 27-kd heat shock protein (HSP27)-p38 kinase pathway linked to the Ca-independent zipper interacting protein (ZIP)-like or ZIP-kinase. ILK, ZIP-like, or ZIP kinase may directly phosphorylate myosin light chains (MLC₂₀), and they may phosphorylate the targeting subunit of myosin phosphatase (MYPT1) or CPI-17, inhibiting phosphatase activity. CPI-17 (17-kd PKC-dependent phosphatase inhibitor) may also be directly phosphorylated by PKC. (Source: Harnett et al.,³ with permission from the American Physiological Society.)