TRP expression pattern and the functional importance of TRPC3 in primary human T-cells

TRP proteins form ion channels which are activated following receptor stimulation. In T-cell lines, expression data of TRP proteins have been published. However, almost no data about TRP expression is available in primary human T-cells. Using RT-PCR and quantitative RT-PCR, we compare the expression of TRP mRNA in 1) human peripheral blood lymphocytes, which are a mix of mostly mono-nuclear blood lymphocytes but contain other leucocytes, 2) a pure human CD4+ T-helper cell population in the resting (= naïve) and activated (= effector) state, and 3) two commonly used CD4+ Jurkat T-cell lines, E6-1 and parental. To mimic physiological cell stimulation, we analyzed TRP expression in primary human cells in a quantitative way over several days following formation of an immunological synapse through stimulation with antibody-coated beads. The TRP expression profile of primary human T-cells was significantly different from Jurkat T-cells. Among the TRP mRNAs of the TRPC, TRPM, and TRPV family, we found consistent expression of TRPC1, TRPC3, TRPV1, TRPM2, and TRPM7 in primary human CD4+ T-cells of all analyzed blood donors. Among these, TRPC3 and TRPM2 were strongly up-regulated following stimulation, but with different kinetics. We found that TRPC3 modulates Ca2+-dependent proliferation of primary CD4+ T-cells indicating that TRPC3 may be involved in Ca2+ homeostasis in T-cells besides the well-established STIM and ORAI proteins which are responsible for store-operated Ca2+ entry.

Research Highlights
► In primary human CD4+ T-cells, TRPC1, C3, V1, M2, and M7 are consistently expressed.
► TRPC3 and TRPM2 are up-regulated after T-cell stimulation but with different kinetics.
► STIM1 down-regulation reduces resting intracellular [Ca2+].
► TRPC3 down-regulation reduces calcium-dependent T-cell proliferation.