PRAME Is a Golgi-Targeted Protein That Associates with the Elongin BC Complex and Is Upregulated by Interferon-Gamma and Bacterial PAMPs

Abstract

Preferentially expressed antigen in melanoma (PRAME) has been described as a cancer-testis antigen and is associated with leukaemias and solid tumours. Here we show that PRAME gene transcription in leukaemic cell lines is rapidly induced by exposure of cells to bacterial PAMPs (pathogen associated molecular patterns) in combination with type 2 interferon (IFNγ). Treatment of HL60 cells with lipopolysaccharide or peptidoglycan in combination with IFNγ resulted in a rapid and transient induction of PRAME transcription, and increased association of PRAME transcripts with polysomes. Moreover, treatment with PAMPs/IFNγ also modulated the subcellular localisation of PRAME proteins in HL60 and U937 cells, resulting in targeting of cytoplasmic PRAME to the Golgi. Affinity purification studies revealed that PRAME associates with Elongin B and Elongin C, components of Cullin E3 ubiquitin ligase complexes. This occurs via direct interaction of PRAME with Elongin C, and PRAME colocalises with Elongins in the Golgi after PAMP/IFNγ treatment. PRAME was also found to co-immunoprecipitate core histones, consistent with its partial localisation to the nucleus, and was found to bind directly to histone H3 in vitro. Thus, PRAME is upregulated by signalling pathways that are activated in response to infection/inflammation, and its product may have dual functions as a histone-binding protein, and in directing ubiquitylation of target proteins for processing in the Golgi.

A therapeutic T cell receptor mimic antibody targets tumor-associated PRAME peptide/HLA-I antigens

“…Despite promising results, a major limitation of currently marketed mAbs is that they bind exclusively to cell-surface and extracellular antigens, whereas the majority of aberrantly expressed proteins in cancer, including PRAME, are intracellular (1,11,12,15). We hypothesized that a TCRm Ab directed against the peptide-HLA complex formed by ALY and HLA-A2 would be capable of specifically binding to PRAME-expressing tumors and would be a cancer therapeutic against a formerly untargetable protein.…”

“…Only minimal positive shifts in median fluorescence intensity (MFI) After the preliminary biochemical and specificity characterization, we sought to determine whether Pr20 could recognize cancer cells expressing endogenous PRAME protein. PRAME mRNA expression was assessed by quantitative PCR (qPCR), and surface HLA-A2 expression and Pr20 binding were assessed by flow cytometry across a panel of HLA-A2 + hematopoietic and solid tumor cell lines, several of which have been reported to express PRAME by other groups (10,12,16,30,31) (Table 1 and Figure 1C). Pr20 binding was readily detected in PRAME + HLA-A2 + leukemia AML14, SET2, BV173, and the T cell lymphoma MAC2A, demonstrating that Pr20 can detectably bind endogenously processed and presented peptides ( Figure 1D).…”

“…This tumor-selective expression profile makes PRAME a highly attractive therapeutic target. PRAME is an intracellular protein (1,11,12), making it impossible to target using traditional Abs directed at cell-surface proteins, and it cannot currently be inhibited using small molecules. Its function in tumor progression is complex, and in some contexts, PRAME overexpression can reduce malignancy Preferentially expressed antigen in melanoma (PRAME) is a cancer-testis antigen that is expressed in many cancers and leukemias.…”

Chemoresistance of PRAME-expressing melanoma cell can be resolved with help of bortezomib

“…Возможностью для снижения уровня активности гена PRAME может быть блокирование внутриклеточных сигнальных путей. Так, в культуре трансформированных клеток НL60 экспрессия PRAME может быть опосредована провоспалительными сигнальными путями, в том числе, возможно, и NF-κB, так как промотор гена PRAME имеет последовательности, распознающиеся субъединицами RelA комплекса NF-κB [7]. Некоторые препараты способны блокировать инициацию передачи сигнала по NF-κB-зависимому пути.…”

“…Один из таких препаратов -дексаметазон, применяемый для купирования воспаления [8]. Известно также, что белок PRAME является компонентом комплекса убиквитинлигазы E2 [7]. Функция PRAME в этом комплексе заключается в распознавании белковых субстратов, которые убиквитинируются и деградируют в протеасоме.…”