Aberrant PDGFRA Signalling Is Sustained by An Autocrine Loop in Peripheral T-Cell Lymphoma Not Otherwise Specified

Background. Peripheral T-cell lymphoma not otherwise specified (PTCL/NOS) is the most common T-cell lymphoma; however, it remains a complex entity showing great variety regarding morphology, immunophenotype and clinical behaviour. Recently, gene expression profiling (GEP) revealed PDGFRA as possible PTCL-associated molecule, by nominating it as potential therapeutic target.

Aims and Methods. We investigated the possible determinants of PDGFRA activity in PTCL/NOS. We performed GEP of 28 PTCLs/NOS and 20 samples of normal T-cell subpopulations, by using the Affymetrix HG-U133 2.0 plus microarray. Moreover, we built tissue-microarrays (TMAs) including 145 PTCLs/NOS for protein analyses. The PDGFRA locus (4q1.1–4q1.3) was studied by FISH on those TMAs, while direct sequencing of all PDGFRA exon and introns as well as of the promoter region was performed in 90 cases. Immunohistochemistry (IHC) and ELISA were adopted in order to study the expression of PDGF-A, PDGF-B and PDGF-C on tissue sections and in supernatants from PTCL/NOS cell cultures, respectively. Finally, the expression of PDGFRA and its activated (phosphorilated) form, p-PDGFRA, was assessed by IHC on TMAs, and by flow-citometry in PTCL/NOS cultured cells before and after the exposure to an anti-PDGF ligand neutralizing antibody (R&B System).

Results. First, GEP showed over-expression of PDGFRA in all tested PTCLs/NOS, while IHC confirmed the expression of PDGFRA and p-PDGFRA. FISH, SNPs analysis and direct sequencing showed preserved integrity of PDGRA locus. We then studied PDGF-A, PDGF-B and PDGF-C, which turned out to be expressed and secreted by PTCL/NOS cells. In order to verify the hypothesis of an autocrine loop, we tested whether the remotion of PDGF ligands from the supernatants of cultured PTCL/NOS cells determined PDGFRA de-phosphorilation. Notably, 48h after the exposure to 20 mg of anti-PDGF antibody, we already appreciated a significant effect with reduction of PDGFRA phosphorilation up to 75%.

Conclusions. Taken together, our data demonstrate that PDGFRA activity is sustained by an autocrine loop in PTCL/NOS.