Immunomodulatory pathways regulate expression of a spliced FKBP51 isoform in lymphocytes of melanoma patients

Abstract

FKBP51 (gene FKBP5) is an immunophilin capable of immunosuppression expressed in melanoma and lymphocytes. We found increased levels of a spliced FKBP5 variant in the PBMCs of 124 patients with melanoma. This variant encodes for an unknown isoform (FKBP51s). We hypothesized that FKBP51s resulted from tumour interaction with immune cells, through PDL-1/PD-1. To address this issue, we performed melanoma/PBMC cocultures. Furthermore, the immunohistochemistry of 76 melanoma specimens served to investigate whether FKBP51s stained tumour infiltrating lymphocytes. Our results showed that PBMCs expressed FKBP51s when cocultured with melanoma. Tumour PDL-1 knockdown or anti-PD-1 reduced FKBP51s expression in cocultured PBMCs. IHC showed a strong FKBP51s signal in tumour infiltrating lymphocytes, and lymphocytes of the invasion front of the tumour, along with melanoma PDL-1 expression. When overexpressed in melanoma, FKBP51s facilitated PDL-1 expression on the cell surface. In conclusion, our study shows that FKBP51s marks the PBMCs of patients with melanoma and is exploited by the tumour to immunomodulate through PDL-1.

A regulatory role for the co-chaperone FKBP51s in PD-L1 expression in glioma

“…As shown in Figure 1A , both the canonical and the spliced FKBP51 isoforms were expressed in the glioblastoma cells. Whereas in melanoma, FKBP51s was barely detected under basal conditions [ 16 ]. FKBP51s expression in glioblastoma cells was confirmed by fluorescent microscopy (Figure 1B ), showing a localization in both nuclear and cytoplasmic compartments (Figure 1B ).…”

“…The targeting of mechanisms that control post-translational modification can help in neutralizing the pro-tumoral effect of PD-L1. Our research has previously identified a role for a spliced variant of the FKBP5 gene in the regulation of PD-L1 expression in melanoma [ 16 ]. FKBP5 encodes a large immunophilin which was originally cloned in lymphocytes [ 17 ] but also found abundantly expressed in several tumours [ 18 – 23 ], including glioblastoma [ 24 ].…”

“…The FKBP51 protein structure includes a C-terminal TPR three tandem repeat domain, responsible for protein-protein interaction, and two N-terminal FK506 binding domains (FKBP), of which the most N-terminal one exerts a peptidyl-prolyl isomerase (PPIase) activity [ 25 ]. The spliced isoform (isoform 2 or FKBP51s) [ 16 ] lacks a TPR domain and has a distinct C-terminus compared to isoform 1. Isoform 2 resulted induced, bidirectionally, in melanoma and lymphocytes following their interaction through the PD-L1/PD1 ligand/receptor system [ 16 ].…”

“…The spliced isoform (isoform 2 or FKBP51s) [ 16 ] lacks a TPR domain and has a distinct C-terminus compared to isoform 1. Isoform 2 resulted induced, bidirectionally, in melanoma and lymphocytes following their interaction through the PD-L1/PD1 ligand/receptor system [ 16 ]. Classically, the PPIase activity of FKBPs is inhibited by the immunosuppressant agents rapamycin and FK506.…”

Expression of FK506‐binding protein 51 (FKBP51) in Mycosis fungoides

“…38 Gene expression was performed using the SsoAdvancedTM SYBR Green Supermix (Bio-Rad, Hercules, CA, USA), and specific qPCR primers to analyse each transcript, particularly, to detect FKBP51, X-linked inhibitor of apoptosis protein (XIAP) and BCL-2 validated QuantiTec primers from Qiagen (Valencia, CA, USA) were used, along with co-amplified ribosomal 18S and b-Actin as internal controls for normalization. 28,48 For the comparison between thymus, skin cases and MF groups, quantitative gene expression for FKBP51 was performed with the 2 ÀDCT comparative method. Quantitative gene expression for FKBP51, XIAP and BCL-2 in MF cases was performed as relative expression change fold using normal thymus as reference sample.…”