Nascent Polypeptide Associated Complex Protein Alpha (NACa)

alpha-NAC, an osteoblast-specific AP-1 coactivator that potentiates the transcriptional activity of the c-Jun/c-Jun homodimer. Positive immunostaining for JNK1, JNK2, p-JNK, c-Jun, pc-Jun, c-Fos, and alpha-NAC was observed in 86, 93, 94, 99, 97, 99, and 97.5% of the samples, whereas normal bone was devoid of these immunoreactivities. Moreover, significantly higher expression levels of all proteins were detected in high-grade tumors compared to levels in low-grade ones. The observed expression profile of alpha-NAC implies that the active AP-1 in human osteosarcomas most likely comprises c-Jun/c-Jun homodimers. When cellular levels of the JNK pathway components and c-Fos were evaluated as possible biological markers of tumor grade, high expression of c-Jun and abundant pc-Jun predicted a high-grade tumor.