描述:
The Protein Kinase C (PKC) family of homologous serine/threonine protein kinases is involved in a number of processes, such as growth,
differentiation, and cytokine secretion. At least eleven isozymes have been described. These proteins are products of multiple genes and
alternative splicing. PKC consists of a single polypeptide chain containing four conserved regions (C) and five variable regions (V). The
N-terminal half containing C1, C2, V1, and V2 constitutes the regulatory domain and interacts with the PKC activators Ca2+, phospholipid,
diacylglycerol, or phorbol ester. However, the novel PKC (nPKC) subfamily members (δ, ε, η, and θ isoforms) and the atypical PKC (aPKC)
subfamily members (ζ, ι, and λ isoforms) are Ca2+-independent and lack the C2 domain. The aPKC members are unique in that their activity
is independent of diacylglycerols and phorbol esters. They also lack one repeat of the cysteine-rich sequences that are conserved in cPKC and
nPKC members. The C-terminal region of PKC contains the catalytic domain. The PKC pathway represents a major signal transduction system
that is activated following ligand-stimulation of transmembrane receptors by hormones, neurotransmitters, and growth factors. PKCθ
transcripts are expressed in most tissues with the highest levels being found in hematopoietic tissues and cell lines, including T cells and
thymocytes. PKCθ mRNA is readily detectable in skeletal muscle, lung and brain. However, PKCθ expression is not detected in several human
carcinoma cell lines. Abundant expression of this PKC isozyme in hematopoietic cells suggest that it may have a role in growth and
differentiation processes of these cells.