Phorbol 12,13-dibutyrate, a phorbol ester, is an activator of PKC, including the conventional calcium-dependent subtypes (α and γ), the nonconventional calcium-independent isoforms (δ, ε, η), as well as the atypical calcium-independent and DAG or phorbol ester-unresponsive subtype (ζ). PKC plays an important role in the regulation of a variety of cellular processes such as exocytosis, gene expression, cell proliferation and differentiation, as well as tumor promotion, thereby representing the major target for tumor-promoting phorbol esters and chemically unrelated tumor promoters. Phorbol esters are able to replace the endogenous activator DAG in the stimulation of PKC, and participate in the multistage process of tumor formation and progression.
References:
1. Geiges D, Meyer T, Marte B, et al. Activation of protein kinase C subtypes alpha, gamma, delta, epsilon, zeta, and eta by tumor-promoting and nontumor-promoting agents. Biochemical Pharmacology, 1997, 53(6): 865-875.
2. Middleton JP, Khan WA, Collinsworth G, et al. Heterogeneity of protein kinase C-mediated rapid regulation of Na/K-ATPase in kidney epithelial cells. Journal of Biological Chemistry, 1993, 268(21): 15958-15964.
3. Scribner JD, Boutwell RK. Inflammation and tumor promotion: selective protein induction in mouse skin by tumor promoters. European Journal of Cancer, 1972, 8(6): 617-621.