Expression of a MYCN-interacting isoform of the tumor suppressor BIN1 is reduced in neuroblastomas with unfavorable biological features.

PURPOSE: Amplification of the MYCN proto-oncogene is strongly correlated with poor outcome in neuroblastoma (NB), although deregulated MYCN is a potent inducer of apoptosis. BIN1 (2q14) encodes multiple isoforms of a Myc-interacting adaptor protein that has features of a tumor suppressor, including the ability to inhibit Myc-mediated cell transformation and to promote apoptosis. We hypothesized that BIN1 may function as a suppressor gene in NB, because Bin1 is highly expressed in neural tissues and binds the Myc Box motifs that are conserved in MycN. EXPERMENTAL DESIGN: Expression of MYCN, total BIN1, and BIN1 isoforms were determined in 56 primary NBs using the real-time PCR. Expression was correlated with biological and genetic features. To determine the functional significance of BIN1 expression we ectopically expressed BIN1 isoforms in NB cell lines with and without MYCN amplification, and assessed clonogenic growth.

RESULTS: Four predominant BIN1 isoforms resulting from alternative splicing of exon 12A (a neural tissue-specific exon) and exon 13 (a Myc-binding domain encoding exon) were variably expressed in the 56 primary NBs. Expression of BIN1 was lower in: NBs with MYCN amplification (n = 10) compared with those without, P < 0.03; in International Neuroblastoma Risk Group high-risk NB (n = 19) compared with low- or intermediate-risk NB, P < 0.01; and in metastatic NB (n = 21) compared with localized NB, P < 0.06. BIN1 inactivation by deletion or genomic rearrangement was identified infrequently. Forced expression of BIN1 isoforms containing the Myc-binding domain (with or without exon 12A) inhibited colony formation in NB cell lines with MYCN amplification (P < 0.01) but not in those without. Forced expression of BIN1 isoforms with a MBD deletion did not inhibit colony formation in any cell line assessed.

CONCLUSIONS: These data support that reduced BIN1 expression contributes to the malignant phenotype of childhood NB. As we reported previously, BIN1 may function to circumvent MycN-mediated apoptosis in NBs with MYCN amplification.