Notch receptors in human choroid plexus tumors

Notch signaling plays a role in development and formation of the normal choroid plexus (nCP), and in formation of various tumors in humans. Activation of Notch3 has been reported to promote tumor growth in invasive gliomas and to initiate formation of choroid plexus tumors (CPT) in mice. We investigated the expression of all currently known Notch receptors (Notch 1-4) in 55 samples of nCP and 88 CPT, including 61 choroid plexus papillomas (CPP), 22 atypical CPP and 5 choroid plexus carcinomas by immunohistochemistry. Notch expression was semiquantitatively evaluated separately for membranous/cytoplasmic and for nuclear staining. In addition, we examined Her2 expression (EGFR2, Her2/neu, ErbB2, CD340) because of its functional link to Notch signaling. All samples were negative for Notch3. Membranous/cytoplasmic expression of Notch1 (p<0.0001) and Notch4 (p=0.046) was significantly higher, whereas Notch2 expression was significantly lower (p<0.0001) in nCP compared to CPT. Nuclear expression of Notch1, -2 and -4 was significantly higher in CPT compared to nCP (p<0.0001 each). Expression of Notch2 and Notch4 showed a shift from a prevailing membranous/cytoplasmic expression in nCP to a predominant nuclear expression in CPT. Her2 was weakly expressed in 42/84 CPT but only in 2/53 nCP (p=0.0001) and positively correlated with nuclear expression of Notch1, -2 and 4 in CPT. In summary, a shift between membranous/cytoplasmic (non-canonical signaling pathway) and nuclear expression (canonical signaling pathway) of Notch1, -2 and -4 and upregulation of Her2 indicate neoplastic transformation in human CP and may reveal new therapeutic approaches.