Identification of a novel splice variant of human PD-L1 mRNA encoding an isoform-lacking Igv-like domain
Abstract
Aim: To investigate the expression and regulation of PD-1 ligand 1 (PD-L1) in
peripheral blood mononuclear cells (PBMC). Methods: The cDNA encoding human
PD-L1 precursor was cloned from the total RNA extracted from the resting
and phorbol dibutyrate plus ionomycin- or phytohemagglutinin-activated PBMC,
by reverse transcription polymerase chain reaction (RT-PCR), and independent
clones were sequenced and analyzed. The expression and subcellular localization
were examined in transiently transfected cells. The PD-L1 gene expression in
different PBMC was also analyzed by RT-PCR. Results: A novel human PD-L1
splice variant was identified from the activated PBMC. It was generated by splicing
out exon 2 encoding an immunoglobulin variable domain (Igv)-like domain but
retaining all other exons without a frame-shift. Consequently, the putative translated
protein contained all other domains including the transmembrane region
except for the Igv-like domain. Furthermore, the conventional isoform was expressed
on the plasma surface whereas the novel isoform showed a pattern of
intracellular membrane distribution in transiently transfected K562 cells. In addition,
the expression pattern of the PD-L1 splice variant was variable in different individuals
and in different cellular status. Conclusion: PD-L1 expression may be
regulated at the posttranscriptional level through alternative splicing, and modulation
of the PD-L1 isoform expression may influence the outcome of specific
immune responses in the peripheral tissues.
Keywords:
peripheral blood mononuclear cells (PBMC). Methods: The cDNA encoding human
PD-L1 precursor was cloned from the total RNA extracted from the resting
and phorbol dibutyrate plus ionomycin- or phytohemagglutinin-activated PBMC,
by reverse transcription polymerase chain reaction (RT-PCR), and independent
clones were sequenced and analyzed. The expression and subcellular localization
were examined in transiently transfected cells. The PD-L1 gene expression in
different PBMC was also analyzed by RT-PCR. Results: A novel human PD-L1
splice variant was identified from the activated PBMC. It was generated by splicing
out exon 2 encoding an immunoglobulin variable domain (Igv)-like domain but
retaining all other exons without a frame-shift. Consequently, the putative translated
protein contained all other domains including the transmembrane region
except for the Igv-like domain. Furthermore, the conventional isoform was expressed
on the plasma surface whereas the novel isoform showed a pattern of
intracellular membrane distribution in transiently transfected K562 cells. In addition,
the expression pattern of the PD-L1 splice variant was variable in different individuals
and in different cellular status. Conclusion: PD-L1 expression may be
regulated at the posttranscriptional level through alternative splicing, and modulation
of the PD-L1 isoform expression may influence the outcome of specific
immune responses in the peripheral tissues.