Defects at the Posttranscriptional Level Account for the Low TCR Chain Expression Detected in Gastric Cancer Independently of Caspase-3 Activity.

BACKGROUND

Reduced TCR chain surface has been reported in T cells from patients with different inflammatory conditions and cancer. However, the causes of this diminished expression in cancer remain elusive.

METHODS

T cell-enriched populations of blood or tissue (tumoral and nontumoral) origin from 44 patients with gastric adenocarcinoma and 33 healthy subjects were obtained. Samples were subjected to cytofluorimetry, Western blot analysis, TCR cDNA sequencing experiments, measurement of TCR mRNA levels, and caspase-3 activity assays.

RESULTS

Cytofluorimetry revealed a decreased TCR expression in T cells of patients, assessed either as percentage of cells expressing this chain (blood: control subjects 99.8 ± 0.1%, patients 98.8 ± 1.1% < 0.001; tissue: control subjects 96.7 ± 0.9%, patients tumoral tissue 67.9 ± 27.0%, patients nontumoral tissue 82.8 ± 12.6%, = 0.019) or mean fluorescence intensity (MFI) value (blood: control subjects 102.2 ± 26.0; patients 58.0 ± 12.3, = 0.001; tissue: control subjects 99.4 ± 21.4; patients tumoral tissue 41.6 ± 21.4; patients nontumoral tissue 62.3 ± 16.6, = 0.001). Other chains pertaining to the TCR-CD3 complex (CD3) showed no significant differences (MFI values). Subsequent TCR cDNA sequencing experiments or measurements of TCR mRNA levels disclosed no differences between patients and control subjects. Evaluation of caspase-3 activity showed higher levels in T cell extracts of patients, and this activity could be decreased by 70% with the use of the inhibitor Ac-DEVD-FMK, although CD3 expression levels did not recover.

CONCLUSIONS

These results further place the defect responsible for the low TCR expression in cancer at the posttranscriptional level and suggests contrary to what has been proposed in other pathologies that elevated caspase-3 activity is not the causative agent.