Interleukin-13 receptor alpha chain: A novel tumor-associated transmembrane protein in primary explants of human malignant gliomas

Human malignant glioma cell lines express high levels of interleukin-13 rec eptor (IL-13R), However, the subunit structure of this receptor in primary brain tumor cells is not known. Herein, we examined the subunit composition of IL-13R by analyzing the expression of four different putative subunits of IL-13R complex in 25 primary explants of malignant brain tumors. Reverse transcription-PCR (RT-PCR) of RNA from these tumor cells, normal astrocyte s, and normal brain tissue showed that transcripts of IL-13R alpha chain we re present in greater abundance in malignant glioma cells compared with nor mal astrocytes or normal brain tissues. The transcripts for two other chain s (e.g., IL-13R alpha' and IL-4R beta), on the other hand, yielded similar PCR positivity in brain tumors as well as in normal samples, whereas transc ripts for gamma c chain were absent in all brain tumor cells and normal tis sues. The specificity of RT-PCR products for these genes was confirmed by o ligo liquid hybridization analysis using a radiolabeled sequence-specific i nternal probe. Indirect immunofluorescence studies for different receptor c hains confirmed the RT-PCR results and demonstrated a striking difference i n the level of expression of IL-13R alpha protein between normal astrocytes and malignant astrocytoma cells. These studies establish the IL-13R alpha subunit as a novel tumor-specific protein that may be useful as a tumor mar ker, a target for cytotoxin/immunotoxin, or alternatively, a tumor-associat ed antigen for active, specific immunotherapy.