You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["RNA", "CellLine", "Protein", "DNA", "CellType"].

Please return the output as a JSON object of the format: {"DNA" : ["TAL1", ...], "RNA": ["mRNAs", ...], "CellLine": ["T cells", ...], "CellType": ["monocytes", ...], "Protein": ["IL-2", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Cell-specific expression of helix-loop-helix transcription factors encoded by the E2A gene. The E2A gene encodes transcription factors of the helix-loop-helix family that are implicated in cell-specific gene expression as part of dimeric complexes that interact with E box enhancer elements. It has previously been shown that transcripts of the E2A gene can be detected in a wide range of cell types. We have now examined expression of the mouse E2A gene at the protein level using polyclonal antisera directed against distinct portions of the E2A protein to probe blots of cellular extracts. A 73 kDa protein was identified by this analysis: this protein is highly enriched in cell lines of B lymphoid origin as compared to pancreatic beta-cells and fibroblast cells. The detection of this protein selectively in extracts of lymphoid cells correlates with the presence of the E box-binding activity LEF1 / BCF1 in these cells; this binding activity was previously shown to be efficiently recognized by antiserum directed against E2A gene products. Transfection of cells with full length E2A cDNA leads to appearance of protein co-migrating with the 73 kDa protein on SDS gel electrophoresis and co-migrating with LEF1 / BCF1 on mobility shift analysis. Our results are consistent with the view that the DNA-binding activity LEF1 / BCF1 is a homodimer of E2A proteins; the selective appearance of this putative cell-specific transcription factor in B lymphoid cells seems to be attributable, at least in part, to the elevated E2A protein concentrations in these cells.
{"CellLine": ["cell lines of B lymphoid origin"], "CellType": ["these cells", "pancreatic beta - cells", "fibroblast cells", "lymphoid cells", "B lymphoid cells"], "DNA": ["mouse E2A gene", "E2A gene", "E2A cDNA", "E box enhancer elements", "E box"], "Protein": ["LEF1 / BCF1", "helix - loop - helix transcription factors", "transcription factors of the helix - loop - helix family that are implicated in cell - specific gene expression", "73 kDa protein", "dimeric complexes", "E2A gene products", "helix - loop - helix family", "homodimer of E2A proteins", "E2A protein", "transcription factors"], "RNA": []}