Effects of PKI55 protein, an endogenous protein kinase C modulator, on specific PKC isoforms activity and on human T cells proliferation.
PKI55 protein, coded by the recently identified KI55 gene [R. Selvatici, E. Melloni, M. Ferrati, C. Piubello, F.C. Marincola, E. Gandini, J. Mol. Evol. 57 (2003) 131-139] is synthesized following protein kinase C (PKC) activation and acts as a PKC modulator, establishing a feedback loop of inhibition. In this work, PKI55 was found to inhibit recombinant alpha, beta(1), beta(2), gamma, delta, zeta and eta PKC isoforms; the effect on conventional PKC was lost in the absence of calcium. Confocal immunofluorescence experiments showed that PKI55 can penetrate into peripheral blood mononuclear cells (PBMC), following a coordinated movement of calcium ions. The addition of PKI55 protein down-regulated the PKC enzyme activity in phytohaemagglutinin-activated PBMC, decreasing the activity of alpha, beta(1) and beta(2) PKC isoforms. Moreover, inhibition in PBMC proliferation was observed. Similar effects were detected in Jurkat T cells transfected with a plasmid containing the coding sequence of PKI55. The PKI55 protein functional role could be to control the pathological over-expression of specific PKC isoforms and to regulate proliferation.
Selvatici
Rita
R
Department of Experimental and Diagnostic Medicine, Medical Genetics Section, University of Ferrara, via Fossato di Mortara 74, Ferrara, Italy. svr@unife.it
Falzarano
Sofia
S
Franceschetti
Lara
L
Spisani
Susanna
S
Siniscalchi
Anna
A
D002118:Calcium / Q000378:metabolism; D002448:Cell Adhesion; D002462:Cell Membrane / Q000378:metabolism; D049109:Cell Proliferation; D003001:Cloning, Molecular; D006801:Humans; D019169:Jurkat Cells; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D008213:Lymphocyte Activation; D018613:Microscopy, Confocal; D020033:Protein Isoforms; D011493:Protein Kinase C / Q000737:chemistry / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry; D013601:T-Lymphocytes / Q000201:enzymology*; D013997:Time Factors
C521057:PKI55 protein, human; D020033:Protein Isoforms; D011506:Proteins; D011994:Recombinant Proteins; D011493:Protein Kinase C; D002118:Calcium