PKC delta (PKCδ) is a serine/threonine kinase that plays a critical role in various cellular processes, including signal transduction, apoptosis, proliferation, survival, transcription, hormonal regulation, and immune responses. It is a 78 kDa protein encoded by the PRKCD gene and is structurally divided into a regulatory and a catalytic domain, containing four constant (C) and five variable (V) regions. PKCδ is activated by diacylglycerol produced by receptor-mediated hydrolysis of membrane inositol phospholipids as well as by tumor-promoting phorbol ester through the binding of these compounds to the C1 region in its regulatory domain. It can also be activated without proteolysis through the tyrosine phosphorylation reaction. PKCδ is involved in the control of growth, differentiation, and apoptosis, and its activation patterns and roles in various pathways are complex and not fully understood. In the immune system, PKCδ is particularly important for peripheral B-cell development and immune homeostasis, with mouse models indicating a special role in the control of B-cell tolerance. PKCδ is also linked to human autoimmune disorders, such as systemic lupus erythematosus (SLE), and is involved in the regulation of survival, proliferation, and apoptosis in various cells including lymphocytes.
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