Expression of classical protein kinase C subspecies in non-neoplastic lymphocytes and non-Hodgkin's lymphomas: an immunohistochemical study

Evidence that PKCα inhibition in Dalton's Lymphoma cells augments cell cycle arrest and mitochondrial-dependent apoptosis

Protein kinase Cα (PKCα), belonging to ser/thr protein kinase, perform various biological functions. Overexpression of PKCα has been observed in multiple human malignancies including lymphoma. However, the molecular pathogenesis and involvement of PKCα in Non-Hodgkin lymphoma (NHL) are not clearly understood. Hence, deciphering the role of PKCα in NHL management may provide a better therapeutic option. In the present study, we used selective pharmacological inhibitors Gö6976 and Ro320432 that potentially inhibit PKCα-mediated signaling in DL cells, resulting in the inhibition of cell growth and mitochondrial-dependent apoptosis. PKCα inhibition by these inhibitors also displays cell cycle arrest at the G1 phase and causes growth retardation of DL cells. Our results extended the mechanism of PKCα in NHL, and provided potential implications for its therapy.

Open-label, single-arm, phase II study of enzastaurin in patients with follicular lymphoma

This open-label, phase II study investigated whether enzastaurin, a protein kinase C-beta (PKCβ) inhibitor, had activity in patients with grade 1 or 2 follicular lymphoma (FL). Adults with grade 1 or 2 FL who had no more than one prior treatment received oral enzastaurin continuously for up to 3 years. Of the 66 patients who received enzastaurin, 53 were evaluable for response. Overall response rate (ORR, primary efficacy endpoint) was 26.4% (3.8% complete response). Median (95% confidence interval) progression-free survival, time to response, and duration of response were 18.1 (11.5-28.3), 4.9 (2.8-8.1), and 22.3 (8.8-not applicable) months, respectively. In patients with tumour tissue available for biomarker analysis, ORRs in low versus high PKCβ2 expression groups were 41.7% and 8.3%, respectively (P = 0.041). The most common, mainly low-grade drug-related adverse events were fatigue (25.8%), diarrhoea (25.8%), nausea (18.2%), and chromaturia (18.2%). Four (6.1%) patients had Grade 3 toxicity and one (1.5%) patient had Grade 4 toxicity. Enzastaurin demonstrated limited clinical activity in grade 1 or 2 FL. Patients with low PKCβ2 expression in tumours had higher ORR than those with high PKCβ2 expression. Enzastaurin was well tolerated with mostly grade 1 or 2 toxicities. Further studies may be warranted in select patient populations.

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.

Expression of PKC-beta or cyclin D2 predicts for inferior survival in diffuse large B-cell lymphoma

We sought to determine whether identification of poor-risk subgroups of diffuse large B-cell lymphoma (DLBCL) using immunohistochemical stains would have practical utility with regard to prognosis and therapeutic decisions. Tissue microarray blocks were created using replicate samples of formalin-fixed, paraffin-embedded tissue from 200 cases of de novo DLBCL. The sections were stained with antibodies to proteins that are expressed by activated or proliferating B cells including MUM1, FOXP1, bcl-2, survivin, protein kinase C-beta (PKC-beta), cyclin D2, cyclin D3, and Ki-67. In univariate analysis, tumor expression of cyclin D2 (P = 0.025) or PKC-beta (P = 0.015) was associated with a worse overall survival, whereas none of the other markers was predictive of overall survival. Patients with DLBCL that expressed either cyclin D2 or PKC-beta had a 5-year overall survival of only 30% as compared to 52% for those who were negative for both markers (P = 0.0019). In multivariate analysis, the expression of cyclin D2 or PKC-beta was an independent predictor of poor overall survival (P = 0.035). Cyclin D2 and PKC-beta expression will be useful in designing a 'biological prognostic index' for patients with DLBCL.

Characterization of expression of protein kinase C isozymes in human B-cell lymphoma: Relationship between its expression and prognosis

Protein kinase C (PKC) enzymes play a major role in signal transduction and contribute to the regulation of cellular differentiation and proliferation. However, little is known about subtype-specific intracellular expression of PKC in human malignant lymphoma. To characterize the relationship between expression of PKC and B-cell lymphomas based on the different subspecies, we investigated the expression of four subspecies (alpha, beta II, gamma and delta) in five cases of reactive lymphoid tissues, 77 cases of human B-cell lymphoma and 17 human lymphoma cell lines. In the reactive lymphoid tissues, PKC beta II-positive cells were found in the mantle zones and marginal zones, and centroblasts and centrocytes in the germinal centers showed cytoplasmic staining with strong intensity against PKC delta. The present study is the first report to examine the expression of PKC delta in reactive lymphoid tissues. In interfollicular areas, a small number of T-cells were positive for PKC alpha. Protein kinase C gamma-positive cells were not found in these lymphoid tissues. Eight cases of Burkitt lymphoma (BL) (8/10; 80%) showed the overexpression of PKC alpha (P < 0.01), but other B-cell lymphoma cases except three cases of diffuse large B-cell lymphoma did not express PKC alpha. In addition, six and eight out of nine BL cell lines expressed the protein and mRNA of PKC alpha, respectively. These results indicate that PKC alpha was predominantly expressed on BL in comparison with other types of lymphoma. The expression of PKC gamma was observed in only five cases of BL. The overall survival of PKC gamma-positive BL was significantly better than that of PKC gamma-negative BL (P < 0.05). The expression of PKC gamma seems to be associated with a better prognosis in the limited number of BL cases in the present study.