Retinal protein kinase C.

Abstract

The protein kinase C (PKC) family of serine/threonine kinase isoenzymes are universally expressed in vertebrate tissues where they control vital cellular functioning. PKC comprises twelve currently identified mammalian isoenzymes, described in three distinct groups according to their need for different effector stimulation. Immunological localisation studies in various vertebrate retinas have indicated the presence, so far, of eight of the PKC subspecies, each with a unique cellular distribution in this tissue. Use of these immunological probing techniques with antibodies raised to the individual PKC family members by immunohistochemistry and western blotting, along with biochemical tools such as the potent activators, the tumour-promoting phorbol esters can hopefully lead to elucidation of the roles of these enzymes in the neural retina. Research work to date has pinpointed a number of roles for PKC in this tissue including control of dopamine release, modulation of glutamate receptor function (probably by a process of direct receptor phosphorylation), phosphorylatory modulation of GABAC-receptor function, an involvement in the retinal ischaemic cascade process (the relevance of which is unknown as yet), involvement in control of cytoskeletal interactions by cytoskeletal element-kinase action and feedback control of enzymes involved in the process of inositol phosphate signalling. PKC has been shown to have an important regulatory role in the process of phototransduction: many of the enzymes and proteins making up the phototransduction cascade act as in vitro and in vivo substrates for PKC-dependent phosphorylation and can have their normal function modified in this way. Also, PKC has been implicated in the control of spinule formation in the retina, a process involved in retinal synaptic plasticity and functioning. All of this work has been described, herein. Collation and utilisation of knowledge of all of the work described here may help us to determine the exact roles for individual isoenzymes in the retina. This in turn may help us to understand and further to prevent pathological conditions leading to inappropriate retinal functioning and possible blindness. Furthermore, understanding the roles of PKC in the neural retina may lead us to vital clues in the understanding of the functioning of this important group of enzymes in the nervous system as a whole and eventually to the prevention of many major neuropathological disorders.