Cellular distribution of protein kinase C isozymes in CD3‐mediated stimulation of human T lymphocytes with aging

Abstract

Protein kinase C (PKC) is involved in a variety of cellular responses, such as the expression and secretion of IL-2, the regulation of cytotoxic killing and cell proliferation. It is known that these immune functions are altered with aging. Here, we show that anti-CD3-triggered T cell proliferation is significantly decreased with aging and that H7, an inhibitor of PKC, impairs the anti-CD3-induced T cell proliferation in a differential manner, lymphocytes of healthy young subjects being more sensitive to the PKC inhibitor than those of elderly subjects. We examined (Western blot) the presence and the cellular distribution of PKC isozymes in T lymphocytes of healthy young and elderly subjects in the resting state and after anti-CD3 mAb stimulation using antibodies directed against PKC 6,/3, 8, e and isoforms in the cytosol and the plasma membrane fractions. These five PKC isotypes were present in human T cells of young and elderly subjects. However, their distribution between the cytosolic and membrane fractions varied according to the isozymes and the age of the subjects. In resting lymphocytes of young subjects, all the PKC isozymes were found in the cytosolic fraction, except PKC-~. In resting lymphocytes of elderly subjects PKC-~ and -e were almost equally distributed between the cytosolic and the membrane fractions, whereas PKC-, and -~ were mainly found in the membrane fraction and PKC-/3 was almost exclusively located in the cytosolic fraction. The translocation of PKC-c~, -/3, -~ and -E could be observed under anti-CD3 mAb stimulation in lymphocytes of young subjects, while in the case of elderly subjects only the PKC ]3 isoform was translocated. Our results suggest that the decreased availability of cytosolic PKC may contribute to the diminished PKC-dependent responses to CD3-triggered stimulation of human T lymphocytes with aging.

Age-related decline in RACK-1 expression in human leukocytes is correlated to plasma levels of dehydroepiandrosterone

“…Defective PKC activation with aging has also been reported by several authors in human monocytes [18,19] and in human T lymphocytes [20,21], and ϳ50% of elderly subjects has significant reduction in PKC activity in B cells [22]. Agerelated impairment of the translocation of PKC is likely to underlie downstream defects in the activation of immune responses in vitro, as diminished generation of cytotoxic effectors, lower production of some cytokines, and reduced proliferative responses, and in vivo, as diminished response to vaccination and increased susceptibility to infections.…”

“…It is indeed emerging that the defect in PKC activation with aging reflects changes in signals that recruit PKC to the membrane rather than alterations in enzyme levels or intrinsic functional capacity [20,44].…”

The Small GTP-Binding Protein Rho Potentiates AP-1 Transcription in T Cells

“…For example, does overexpression of activated Rho regulate the kinase activity of PKC␣? Since we were able to detect this association only in the membrane fraction of cells, it seems likely that the PKC␣ complexed with Rho is in an activated state, as previous studies have indicated that translocation of PKC␣ to the membrane correlates with its activation (16,48). Alternatively, could PKC␣ modulate Rho activity in the cell through direct phosphorylation or indirectly by phosphorylation of a GEF, GDI, GAP, or other intermediate molecule?…”

Age-related impairment of human T lymphocytes’ activation: specific differences between CD4+ and CD8+ subsets

“…These data indicate that impaired expression of the activation marker CD69 in aging by engagement and even by bypassing the TCR. However, reduced activation of lymphocytes from elderly humans seems, therefore, not only to be due to lower expression of CD3 and/or followed by reduced signal transduction (Fulop et al, 1995) after TCR ligation, but also age-related diminished transcription might be involved in our findings (Whisler et al, 1996).…”