gms | German Medical Science

Objective: Proteomic analysis of cerebrospinal fluid and tumor cyst fluid revealed to be a powerful approach for biomarker identification and to study pathological processes. Previously we detected by MALDI-TOF analysis a protein of 6433 Dalton in fluid acquired from cystic glioblastomas. Possible candidates are ApolipoproteinC1 (ApoC1) and Leucine Zipper Protein 6 (LUZP6). ApoC1 is involved in inflammation, as well as in the oncogenesis of multiple types of cancer. LUZP6, on the other hand, is encoded in an open reading frame at the 3’ end of the myotrophin gene on chromosome 7 and its mRNA transcript has been detected in myelodysplastic syndromes. Both proteins have not been described previously in gliomas. The goal of this study was to assess which of these proteins are expressed in glioblastoma cells.

Methods: Fifty glioblastoma samples from patients who underwent open neurosurgical intervention were investigated by immunohistochemistry. For the detection of LuzP6 two custom made antibodies were employed, one recognizing the N-terminus (amino acids 1-29) and one binding at the C-terminus (amino acids 30-58) of the protein, designed according to the mRNA sequence of LUZP6. A commercially available antibody was used for the detection of ApoC1. The presence of each protein was evaluated using a semiquantitative immune reactive score (IRS). Furthermore, we studied the mRNA expression of each protein in a subgroup of 13 samples using quantitative real-time PCR.

Results: Immunohistochemically, LuzP6 was detected in ~93% of glioblastoma samples (median IRS 6 and 9 respectively) and ApoC1 in 50% (median IRS 2.5). All three antibodies showed a homogenous cytoplasmatic staining. In addition, the LUZP6 antibodies revealed an intense staining in the cell nucleus. Furthermore, the antibody directed against the C-terminus of LUZP6 exhibited a more distinct staining compared to the antibody directed against the N-terminus. The analysis of mRNA expression of both genes demonstrated a mean relative expression of ApoC1 of 14.74±6.34 and 1.72±0.46 for LUZP6 (p<0.01). The IRS, however, revealed no linear correlation with the relative gene expression.

Conclusion: Here, we demonstrate for the first time that ApoC1 and LUZP6 mRNA and protein are expressed in cystic glioblastoma. As both proteins may play a role in glioblastoma cyst formation, further investigations should address the question in which cellular sub-type they are expressed in order to evaluate their role in glioblastomagenesis.

Figure 1 [Fig. 1]

Figure 2 [Fig. 2]